Sign in
Search 68hc12
Subscribe to 68hc12
68hc12 by Keywords
68HC1 | 812A4 | 9S12DP256 | Bootloader | CodeWarrior | D60A | Debugger | DP256 | ECT | EEPROM | EVB | Flash | HC1 | HCS12 | I2C | IAR | ICC1 | Interrupts | LCD | M68KIT912DP256 | MC9S12DP256 | MC9S12DP256B | Metrowerks | Motor | MSCAN | Multilink | PLL | Quadrature | SDI | SPI | Transceiver | XFC
Ads
Discussion Groups
Discussion Groups | 68HC12 | OT; brushed DC motor speed measurement
Join our technical discussions about Freescale Microcontrollers: M68HC12. (Freescale Semiconductor is a Subsidiary of Motorola).
PWM-Generation, function of the counter??? - sleidiman - Jun 17 4:20:00 2005
Hello!
NewbieQuestion 2th! :-)
This time a question about PWM:
I need probably a PWM-Frequency approximately = 2KHz.
I have a busclock = 24 Mhz.
When i use Clock A divided by 128, then is Clock A = 187,5KHz.
I set the PWMCAE=0 (left aligned) and PWMPeriod to PWMPER=100.
Thus I have the PWM-Frequency = (Clock A) / PWMPER = 187,5KHz/100 =
1875Hz. Thatīs okay for me! So far so good; I hope thatīs right so far!
When I vary the Duty Cycle by software (1-99), I can adjust the
voltage output in 50mV-steps. (Output Voltage interval: 0-5V -->
5V/100=50mV)
Thatīs my consideration about controlling the output voltage. It is right?
But now the question:
What is the funtion of the counter??? Which value should I choose for
the counter???
Regards
sleidiman
(You need to be a member of 68hc12 -- send a blank email to 68hc12-subscribe@yahoogroups.com )
NewbieQuestion 2th! :-)
This time a question about PWM:
I need probably a PWM-Frequency approximately = 2KHz.
I have a busclock = 24 Mhz.
When i use Clock A divided by 128, then is Clock A = 187,5KHz.
I set the PWMCAE=0 (left aligned) and PWMPeriod to PWMPER=100.
Thus I have the PWM-Frequency = (Clock A) / PWMPER = 187,5KHz/100 =
1875Hz. Thatīs okay for me! So far so good; I hope thatīs right so far!
When I vary the Duty Cycle by software (1-99), I can adjust the
voltage output in 50mV-steps. (Output Voltage interval: 0-5V -->
5V/100=50mV)
Thatīs my consideration about controlling the output voltage. It is right?
But now the question:
What is the funtion of the counter??? Which value should I choose for
the counter???
Regards
sleidiman
(You need to be a member of 68hc12 -- send a blank email to 68hc12-subscribe@yahoogroups.com )
OT; brushed DC motor speed measurement - Peter Lissenburg - Jun 18 23:12:00 2005
Hi all,
and sorry about this off topic, but I need the collective wisdom of the group.
Is it OK, possible, wise, to use the noise spikes of the drive voltage of a
DC motor to measure it's speed?
Thanks for any guidance.
Peter L.
(You need to be a member of 68hc12 -- send a blank email to 68hc12-subscribe@yahoogroups.com )
and sorry about this off topic, but I need the collective wisdom of the group.
Is it OK, possible, wise, to use the noise spikes of the drive voltage of a
DC motor to measure it's speed?
Thanks for any guidance.
Peter L.
(You need to be a member of 68hc12 -- send a blank email to 68hc12-subscribe@yahoogroups.com )
Re: OT; brushed DC motor speed measurement - BobG...@... - Jun 18 23:17:00 2005
In a message dated 6/18/05 11:16:03 P.M. Eastern Daylight Time,
peter@pete... writes:
Is it OK, possible, wise, to use the noise spikes of the drive voltage of a
DC motor to measure it's speed?
====================
Sounds like a clever trick to me. Wish I'd have thought of it before I
bought that expensive tacho!
[Non-text portions of this message have been removed]
(You need to be a member of 68hc12 -- send a blank email to 68hc12-subscribe@yahoogroups.com )
Re: OT; brushed DC motor speed measurement - Donald E Haselwood - Jun 19 0:25:00 2005
Peter,
Clearly, the spikes offer a way to very accurately measure the speed (e.g.
using an HC12 to measure the time between spikes). The key is where and how
does one pick up those noise spikes. The terminals of a DC motor driven by a
battery don't have much for spikes since the battery has such a low internal
impedance.
The big voltage spike takes place on the armature winding that has just broken
contact with the brushes. One might pick this up by stuffing a wire into the
motor to act as a capacitive pick up.
The model airplanes that use electric motors usually have a by-pass cap right
at the motor terminals to reduce radio interference, so this suggests rf
pickup is another possibility.
The current going into the motor does have a ripple. Some (actually many)
years ago I considered using this to measure the speed of the cars on a
track-car set my son had (he moved on to other things before that project got
far).
I would also expect a very large variation between makes of motors, some being
relatively "quiet," and motor load will also have a big affect.
On a DC motor speed is often sensed by the back emf in a bridge circuit
arrangement, however this is an analog solution, and more difficult to get
high accuracy.
Regards,
Donald E Haselwood
On Saturday 18 June 2005 23:12, Peter Lissenburg wrote:
> Hi all,
> and sorry about this off topic, but I need the collective wisdom of
> the group. Is it OK, possible, wise, to use the noise spikes of the drive
> voltage of a DC motor to measure it's speed?
> Thanks for any guidance.
> Peter L.
(You need to be a member of 68hc12 -- send a blank email to 68hc12-subscribe@yahoogroups.com )
Clearly, the spikes offer a way to very accurately measure the speed (e.g.
using an HC12 to measure the time between spikes). The key is where and how
does one pick up those noise spikes. The terminals of a DC motor driven by a
battery don't have much for spikes since the battery has such a low internal
impedance.
The big voltage spike takes place on the armature winding that has just broken
contact with the brushes. One might pick this up by stuffing a wire into the
motor to act as a capacitive pick up.
The model airplanes that use electric motors usually have a by-pass cap right
at the motor terminals to reduce radio interference, so this suggests rf
pickup is another possibility.
The current going into the motor does have a ripple. Some (actually many)
years ago I considered using this to measure the speed of the cars on a
track-car set my son had (he moved on to other things before that project got
far).
I would also expect a very large variation between makes of motors, some being
relatively "quiet," and motor load will also have a big affect.
On a DC motor speed is often sensed by the back emf in a bridge circuit
arrangement, however this is an analog solution, and more difficult to get
high accuracy.
Regards,
Donald E Haselwood
On Saturday 18 June 2005 23:12, Peter Lissenburg wrote:
> Hi all,
> and sorry about this off topic, but I need the collective wisdom of
> the group. Is it OK, possible, wise, to use the noise spikes of the drive
> voltage of a DC motor to measure it's speed?
> Thanks for any guidance.
> Peter L.
(You need to be a member of 68hc12 -- send a blank email to 68hc12-subscribe@yahoogroups.com )
Re: OT; brushed DC motor speed measurement - Peter Lissenburg - Jun 19 4:05:00 2005
Thanks guys,
I'm looking at the CRO with a small motor running. I'm seeing
bursts of spikes which get more numerous and spread over a longer burst as
I increase the speed. Also I think I'm seeing asynchronous spikes as well.
Maybe carbon build up or other dirt under the brush. Sounding a bit hit and
miss, also with the variation between motors and load. This might not be
worth following.
I think it might be best to follow a more conventional line for the moment.
Thanks for your time.
Peter L. At 12:25 AM 19/06/2005 -0400, you wrote:
>Peter,
>
>Clearly, the spikes offer a way to very accurately measure the speed (e.g.
>using an HC12 to measure the time between spikes). The key is where and how
>does one pick up those noise spikes. The terminals of a DC motor driven by a
>battery don't have much for spikes since the battery has such a low internal
>impedance.
>
>The big voltage spike takes place on the armature winding that has just
>broken
>contact with the brushes. One might pick this up by stuffing a wire into the
>motor to act as a capacitive pick up.
>
>The model airplanes that use electric motors usually have a by-pass cap right
>at the motor terminals to reduce radio interference, so this suggests rf
>pickup is another possibility.
>
>The current going into the motor does have a ripple. Some (actually many)
>years ago I considered using this to measure the speed of the cars on a
>track-car set my son had (he moved on to other things before that project got
>far).
>
>I would also expect a very large variation between makes of motors, some
>being
>relatively "quiet," and motor load will also have a big affect.
>
>On a DC motor speed is often sensed by the back emf in a bridge circuit
>arrangement, however this is an analog solution, and more difficult to get
>high accuracy.
>
>Regards,
>
>Donald E Haselwood >
>
>On Saturday 18 June 2005 23:12, Peter Lissenburg wrote:
> > Hi all,
> > and sorry about this off topic, but I need the collective wisdom of
> > the group. Is it OK, possible, wise, to use the noise spikes of the drive
> > voltage of a DC motor to measure it's speed?
> > Thanks for any guidance.
> > Peter L. >
>Yahoo! Groups Links
(You need to be a member of 68hc12 -- send a blank email to 68hc12-subscribe@yahoogroups.com )
I'm looking at the CRO with a small motor running. I'm seeing
bursts of spikes which get more numerous and spread over a longer burst as
I increase the speed. Also I think I'm seeing asynchronous spikes as well.
Maybe carbon build up or other dirt under the brush. Sounding a bit hit and
miss, also with the variation between motors and load. This might not be
worth following.
I think it might be best to follow a more conventional line for the moment.
Thanks for your time.
Peter L. At 12:25 AM 19/06/2005 -0400, you wrote:
>Peter,
>
>Clearly, the spikes offer a way to very accurately measure the speed (e.g.
>using an HC12 to measure the time between spikes). The key is where and how
>does one pick up those noise spikes. The terminals of a DC motor driven by a
>battery don't have much for spikes since the battery has such a low internal
>impedance.
>
>The big voltage spike takes place on the armature winding that has just
>broken
>contact with the brushes. One might pick this up by stuffing a wire into the
>motor to act as a capacitive pick up.
>
>The model airplanes that use electric motors usually have a by-pass cap right
>at the motor terminals to reduce radio interference, so this suggests rf
>pickup is another possibility.
>
>The current going into the motor does have a ripple. Some (actually many)
>years ago I considered using this to measure the speed of the cars on a
>track-car set my son had (he moved on to other things before that project got
>far).
>
>I would also expect a very large variation between makes of motors, some
>being
>relatively "quiet," and motor load will also have a big affect.
>
>On a DC motor speed is often sensed by the back emf in a bridge circuit
>arrangement, however this is an analog solution, and more difficult to get
>high accuracy.
>
>Regards,
>
>Donald E Haselwood >
>
>On Saturday 18 June 2005 23:12, Peter Lissenburg wrote:
> > Hi all,
> > and sorry about this off topic, but I need the collective wisdom of
> > the group. Is it OK, possible, wise, to use the noise spikes of the drive
> > voltage of a DC motor to measure it's speed?
> > Thanks for any guidance.
> > Peter L. >
>Yahoo! Groups Links
(You need to be a member of 68hc12 -- send a blank email to 68hc12-subscribe@yahoogroups.com )
RE: OT; brushed DC motor speed measurement - Jonathan Masters - Jun 19 5:50:00 2005
Peter,
Some time ago I remember seeing a method using back EMF to measure motor
speed without a tachometer. I can't remember if it was Linear technology
or Maxim but a quick search on Google turned up:
http://www.acroname.com/robotics/info/articles/back-emf/back-emf.html
I'd be curious to know if that worked.
Jonathan. -----Original Message-----
From: 68HC12@68HC... [mailto:68HC12@68HC...] On Behalf
Of Peter Lissenburg
Sent: Sunday, 19 June 2005 6:06 PM
To: 68HC12@68HC...
Subject: Re: [68HC12] OT; brushed DC motor speed measurement
Thanks guys,
I'm looking at the CRO with a small motor running. I'm seeing
bursts of spikes which get more numerous and spread over a longer burst
as
I increase the speed. Also I think I'm seeing asynchronous spikes as
well.
Maybe carbon build up or other dirt under the brush. Sounding a bit hit
and
miss, also with the variation between motors and load. This might not be
worth following.
I think it might be best to follow a more conventional line for the
moment.
Thanks for your time.
Peter L. At 12:25 AM 19/06/2005 -0400, you wrote:
>Peter,
>
>Clearly, the spikes offer a way to very accurately measure the speed
(e.g.
>using an HC12 to measure the time between spikes). The key is where
and how
>does one pick up those noise spikes. The terminals of a DC motor
driven by a
>battery don't have much for spikes since the battery has such a low
internal
>impedance.
>
>The big voltage spike takes place on the armature winding that has just
>broken
>contact with the brushes. One might pick this up by stuffing a wire
into the
>motor to act as a capacitive pick up.
>
>The model airplanes that use electric motors usually have a by-pass cap
right
>at the motor terminals to reduce radio interference, so this suggests
rf
>pickup is another possibility.
>
>The current going into the motor does have a ripple. Some (actually
many)
>years ago I considered using this to measure the speed of the cars on a
>track-car set my son had (he moved on to other things before that
project got
>far).
>
>I would also expect a very large variation between makes of motors,
some
>being
>relatively "quiet," and motor load will also have a big affect.
>
>On a DC motor speed is often sensed by the back emf in a bridge circuit
>arrangement, however this is an analog solution, and more difficult to
get
>high accuracy.
>
>Regards,
>
>Donald E Haselwood >
>
>On Saturday 18 June 2005 23:12, Peter Lissenburg wrote:
> > Hi all,
> > and sorry about this off topic, but I need the collective
wisdom of
> > the group. Is it OK, possible, wise, to use the noise spikes of the
drive
> > voltage of a DC motor to measure it's speed?
> > Thanks for any guidance.
> > Peter L. >
>> Service. [Non-text portions of this message have been removed]
(You need to be a member of 68hc12 -- send a blank email to 68hc12-subscribe@yahoogroups.com )
Some time ago I remember seeing a method using back EMF to measure motor
speed without a tachometer. I can't remember if it was Linear technology
or Maxim but a quick search on Google turned up:
http://www.acroname.com/robotics/info/articles/back-emf/back-emf.html
I'd be curious to know if that worked.
Jonathan. -----Original Message-----
From: 68HC12@68HC... [mailto:68HC12@68HC...] On Behalf
Of Peter Lissenburg
Sent: Sunday, 19 June 2005 6:06 PM
To: 68HC12@68HC...
Subject: Re: [68HC12] OT; brushed DC motor speed measurement
Thanks guys,
I'm looking at the CRO with a small motor running. I'm seeing
bursts of spikes which get more numerous and spread over a longer burst
as
I increase the speed. Also I think I'm seeing asynchronous spikes as
well.
Maybe carbon build up or other dirt under the brush. Sounding a bit hit
and
miss, also with the variation between motors and load. This might not be
worth following.
I think it might be best to follow a more conventional line for the
moment.
Thanks for your time.
Peter L. At 12:25 AM 19/06/2005 -0400, you wrote:
>Peter,
>
>Clearly, the spikes offer a way to very accurately measure the speed
(e.g.
>using an HC12 to measure the time between spikes). The key is where
and how
>does one pick up those noise spikes. The terminals of a DC motor
driven by a
>battery don't have much for spikes since the battery has such a low
internal
>impedance.
>
>The big voltage spike takes place on the armature winding that has just
>broken
>contact with the brushes. One might pick this up by stuffing a wire
into the
>motor to act as a capacitive pick up.
>
>The model airplanes that use electric motors usually have a by-pass cap
right
>at the motor terminals to reduce radio interference, so this suggests
rf
>pickup is another possibility.
>
>The current going into the motor does have a ripple. Some (actually
many)
>years ago I considered using this to measure the speed of the cars on a
>track-car set my son had (he moved on to other things before that
project got
>far).
>
>I would also expect a very large variation between makes of motors,
some
>being
>relatively "quiet," and motor load will also have a big affect.
>
>On a DC motor speed is often sensed by the back emf in a bridge circuit
>arrangement, however this is an analog solution, and more difficult to
get
>high accuracy.
>
>Regards,
>
>Donald E Haselwood >
>
>On Saturday 18 June 2005 23:12, Peter Lissenburg wrote:
> > Hi all,
> > and sorry about this off topic, but I need the collective
wisdom of
> > the group. Is it OK, possible, wise, to use the noise spikes of the
drive
> > voltage of a DC motor to measure it's speed?
> > Thanks for any guidance.
> > Peter L. >
>> Service. [Non-text portions of this message have been removed]
(You need to be a member of 68hc12 -- send a blank email to 68hc12-subscribe@yahoogroups.com )
RE: OT; brushed DC motor speed measurement - Peter Lissenburg - Jun 19 6:16:00 2005
Thanks Jonathan,
that's a very well written article. I always thought I knew about
the back EMF idea, but I did have it a bit wrong.
Unfortunately I should have been more explicit, as I need to monitor
displacement rather than speed, although the two are definitely related,
counting pulses seems to be simpler, than integrating speed over time. And
the HC12's timer module is well suited to counting pulses.
But I do have another project that I used the Back EMF idea, and now I know
how to improve it.
So thanks for that as well.
I have just managed to solder on a slotted disc onto the end of the motor
shaft. This will do for a few prototypes. After that we can probably find
one ready made for production.
Thanks again.
Peter L. At 07:50 PM 19/06/2005 +1000, you wrote:
>Peter,
>
>Some time ago I remember seeing a method using back EMF to measure motor
>speed without a tachometer. I can't remember if it was Linear technology
>or Maxim but a quick search on Google turned up:
>http://www.acroname.com/robotics/info/articles/back-emf/back-emf.html
>
>I'd be curious to know if that worked.
>
>Jonathan. >-----Original Message-----
>From: 68HC12@68HC... [mailto:68HC12@68HC...] On Behalf
>Of Peter Lissenburg
>Sent: Sunday, 19 June 2005 6:06 PM
>To: 68HC12@68HC...
>Subject: Re: [68HC12] OT; brushed DC motor speed measurement
>
>Thanks guys,
> I'm looking at the CRO with a small motor running. I'm seeing
>bursts of spikes which get more numerous and spread over a longer burst
>as
>I increase the speed. Also I think I'm seeing asynchronous spikes as
>well.
>Maybe carbon build up or other dirt under the brush. Sounding a bit hit
>and
>miss, also with the variation between motors and load. This might not be
>
>worth following.
>I think it might be best to follow a more conventional line for the
>moment.
>Thanks for your time.
>Peter L. >At 12:25 AM 19/06/2005 -0400, you wrote:
> >Peter,
> >
> >Clearly, the spikes offer a way to very accurately measure the speed
>(e.g.
> >using an HC12 to measure the time between spikes). The key is where
>and how
> >does one pick up those noise spikes. The terminals of a DC motor
>driven by a
> >battery don't have much for spikes since the battery has such a low
>internal
> >impedance.
> >
> >The big voltage spike takes place on the armature winding that has just
>
> >broken
> >contact with the brushes. One might pick this up by stuffing a wire
>into the
> >motor to act as a capacitive pick up.
> >
> >The model airplanes that use electric motors usually have a by-pass cap
>right
> >at the motor terminals to reduce radio interference, so this suggests
>rf
> >pickup is another possibility.
> >
> >The current going into the motor does have a ripple. Some (actually
>many)
> >years ago I considered using this to measure the speed of the cars on a
> >track-car set my son had (he moved on to other things before that
>project got
> >far).
> >
> >I would also expect a very large variation between makes of motors,
>some
> >being
> >relatively "quiet," and motor load will also have a big affect.
> >
> >On a DC motor speed is often sensed by the back emf in a bridge circuit
> >arrangement, however this is an analog solution, and more difficult to
>get
> >high accuracy.
> >
> >Regards,
> >
> >Donald E Haselwood
> >
> >
> >
> >
> >On Saturday 18 June 2005 23:12, Peter Lissenburg wrote:
> > > Hi all,
> > > and sorry about this off topic, but I need the collective
>wisdom of
> > > the group. Is it OK, possible, wise, to use the noise spikes of the
>drive
> > > voltage of a DC motor to measure it's speed?
> > > Thanks for any guidance.
> > > Peter L.
> >
> >
> >
> >> Service. >[Non-text portions of this message have been removed] >
>
>Yahoo! Groups Links
(You need to be a member of 68hc12 -- send a blank email to 68hc12-subscribe@yahoogroups.com )
that's a very well written article. I always thought I knew about
the back EMF idea, but I did have it a bit wrong.
Unfortunately I should have been more explicit, as I need to monitor
displacement rather than speed, although the two are definitely related,
counting pulses seems to be simpler, than integrating speed over time. And
the HC12's timer module is well suited to counting pulses.
But I do have another project that I used the Back EMF idea, and now I know
how to improve it.
So thanks for that as well.
I have just managed to solder on a slotted disc onto the end of the motor
shaft. This will do for a few prototypes. After that we can probably find
one ready made for production.
Thanks again.
Peter L. At 07:50 PM 19/06/2005 +1000, you wrote:
>Peter,
>
>Some time ago I remember seeing a method using back EMF to measure motor
>speed without a tachometer. I can't remember if it was Linear technology
>or Maxim but a quick search on Google turned up:
>http://www.acroname.com/robotics/info/articles/back-emf/back-emf.html
>
>I'd be curious to know if that worked.
>
>Jonathan. >-----Original Message-----
>From: 68HC12@68HC... [mailto:68HC12@68HC...] On Behalf
>Of Peter Lissenburg
>Sent: Sunday, 19 June 2005 6:06 PM
>To: 68HC12@68HC...
>Subject: Re: [68HC12] OT; brushed DC motor speed measurement
>
>Thanks guys,
> I'm looking at the CRO with a small motor running. I'm seeing
>bursts of spikes which get more numerous and spread over a longer burst
>as
>I increase the speed. Also I think I'm seeing asynchronous spikes as
>well.
>Maybe carbon build up or other dirt under the brush. Sounding a bit hit
>and
>miss, also with the variation between motors and load. This might not be
>
>worth following.
>I think it might be best to follow a more conventional line for the
>moment.
>Thanks for your time.
>Peter L. >At 12:25 AM 19/06/2005 -0400, you wrote:
> >Peter,
> >
> >Clearly, the spikes offer a way to very accurately measure the speed
>(e.g.
> >using an HC12 to measure the time between spikes). The key is where
>and how
> >does one pick up those noise spikes. The terminals of a DC motor
>driven by a
> >battery don't have much for spikes since the battery has such a low
>internal
> >impedance.
> >
> >The big voltage spike takes place on the armature winding that has just
>
> >broken
> >contact with the brushes. One might pick this up by stuffing a wire
>into the
> >motor to act as a capacitive pick up.
> >
> >The model airplanes that use electric motors usually have a by-pass cap
>right
> >at the motor terminals to reduce radio interference, so this suggests
>rf
> >pickup is another possibility.
> >
> >The current going into the motor does have a ripple. Some (actually
>many)
> >years ago I considered using this to measure the speed of the cars on a
> >track-car set my son had (he moved on to other things before that
>project got
> >far).
> >
> >I would also expect a very large variation between makes of motors,
>some
> >being
> >relatively "quiet," and motor load will also have a big affect.
> >
> >On a DC motor speed is often sensed by the back emf in a bridge circuit
> >arrangement, however this is an analog solution, and more difficult to
>get
> >high accuracy.
> >
> >Regards,
> >
> >Donald E Haselwood
> >
> >
> >
> >
> >On Saturday 18 June 2005 23:12, Peter Lissenburg wrote:
> > > Hi all,
> > > and sorry about this off topic, but I need the collective
>wisdom of
> > > the group. Is it OK, possible, wise, to use the noise spikes of the
>drive
> > > voltage of a DC motor to measure it's speed?
> > > Thanks for any guidance.
> > > Peter L.
> >
> >
> >
> >> Service. >[Non-text portions of this message have been removed] >
>
>Yahoo! Groups Links
(You need to be a member of 68hc12 -- send a blank email to 68hc12-subscribe@yahoogroups.com )
Re: OT; brushed DC motor speed measurement - test...@... - Jun 19 10:59:00 2005
You did not say whether this was to be a generic method, or tied to a
specific motor. The voltage spikes you may have seen are characteristic of
a low cost motor with poor quality brushes. Larger, industrial motors use
anisotropic graphite brushes, that bridge adjacent commutator segments
without shorting them together. Thus there is a minimum of current
disruption and voltage spiking. Likewise, the signal level will likely
change significantly with brush wear. A series inductor may be required to
enhance the voltage variation, with the consequence of also enhancing brush
wear. At 11:12 PM 6/18/2005, you wrote:
>Hi all,
> and sorry about this off topic, but I need the collective wisdom
> of the group.
>Is it OK, possible, wise, to use the noise spikes of the drive voltage of a
>DC motor to measure it's speed?
>Thanks for any guidance.
>Peter L. >
>
>Yahoo! Groups Links
(You need to be a member of 68hc12 -- send a blank email to 68hc12-subscribe@yahoogroups.com )
specific motor. The voltage spikes you may have seen are characteristic of
a low cost motor with poor quality brushes. Larger, industrial motors use
anisotropic graphite brushes, that bridge adjacent commutator segments
without shorting them together. Thus there is a minimum of current
disruption and voltage spiking. Likewise, the signal level will likely
change significantly with brush wear. A series inductor may be required to
enhance the voltage variation, with the consequence of also enhancing brush
wear. At 11:12 PM 6/18/2005, you wrote:
>Hi all,
> and sorry about this off topic, but I need the collective wisdom
> of the group.
>Is it OK, possible, wise, to use the noise spikes of the drive voltage of a
>DC motor to measure it's speed?
>Thanks for any guidance.
>Peter L. >
>
>Yahoo! Groups Links
(You need to be a member of 68hc12 -- send a blank email to 68hc12-subscribe@yahoogroups.com )
OT: A/D noise on convert - James M. Knox - Jun 19 15:47:00 2005
I've got a data card working with an HC12D60A. Connected to that card by
some short wires (about 6" of #26 stranded) is a little daughter board with
an MCP3002 A/D convertor. For the life of me, I can NOT keep noise off the
Vdd line on the daughter board.
I've got the Vdd run through a ferrite, then a 22 uF, 6 uF, and .1 cap -
all with short leads to the MCP3002. Board has a good ground layer. I'm
getting about 400 mV of noise on the Vdd line (measured directly between
the ground plane and Vdd, right at the filter caps) coincident with the
MCP3002 conversions. Now looking at the data sheet shows only about 5 ma.
max load during conversion, and about .5 ma the rest of the time.
Anyone run into something like this? A load of 5 ma just should NOT be
having that kind of effect. [FWIW, the data line being converted is being
fed from a different Vdd supply.]
jmk
-----------------------------------------------
James M. Knox
TriSoft ph 512-385-0316
1300 Koenig Lane West fax 512-371-5716
Suite 200
Austin, Tx 78756 jknox@jkno...
-----------------------------------------------
(You need to be a member of 68hc12 -- send a blank email to 68hc12-subscribe@yahoogroups.com )
Re: OT: A/D noise on convert - tonalbuilder2002 - Jun 19 20:40:00 2005
> getting about 400 mV of noise on the Vdd line
Maybe the two VDD supplies are "bucking" each other. This would be
most notable if there is a low impedance path between the + supply
voltages. Perhaps you could try using just one of the supplies.
Bill T.
http://www.kupercontrols.com
(You need to be a member of 68hc12 -- send a blank email to 68hc12-subscribe@yahoogroups.com )
Re: OT; brushed DC motor speed measurement - theobee00 - Jun 20 5:50:00 2005
--- In 68HC12@68HC..., Peter Lissenburg <peter@s...> wrote:
> Thanks guys,
> I'm looking at the CRO with a small motor running. I'm seeing
> bursts of spikes which get more numerous and spread over a longer burst as
> I increase the speed. Also I think I'm seeing asynchronous spikes as well.
> Maybe carbon build up or other dirt under the brush. Sounding a bit hit and
> miss, also with the variation between motors and load. This might not be
> worth following.
> I think it might be best to follow a more conventional line for the moment.
Excellent idea, most people go to great lenghts to suppress these for RFI reasons, apart from that the better the motor the lower these spikes and they are hard to separate from mains noise.
Measuring the back EMF is the normal cheap way, I do understand you want to do it on the cheap:-)
I used a switching method once and measured the EMF during the period the power was off (pulsed drive), that avoids getting errors from the drive current so you don't need to compensate, CMOS gate and a cap although in that particular case it was mainly to compensate for the very long cable runs.
Lastly if you use pancake motors drill a hole in the case where the wires bond on the edge, makes an excellent cheap tacho by counting these go past...
Don't forget a spinning motor packs a wallop of energy, do use lots of little resistors before getting too close to the CPU board:-)
Cheers
Theo
> At 12:25 AM 19/06/2005 -0400, you wrote:
> >Peter,
> >
> >Clearly, the spikes offer a way to very accurately measure the speed (e.g.
> >using an HC12 to measure the time between spikes). The key is where and how
> >does one pick up those noise spikes. The terminals of a DC motor driven by a
> >battery don't have much for spikes since the battery has such a low internal
> >impedance.
> >
> >The big voltage spike takes place on the armature winding that has just
> >broken
> >contact with the brushes. One might pick this up by stuffing a wire into the
> >motor to act as a capacitive pick up.
> >
> >The model airplanes that use electric motors usually have a by-pass cap right
> >at the motor terminals to reduce radio interference, so this suggests rf
> >pickup is another possibility.
> >
> >The current going into the motor does have a ripple. Some (actually many)
> >years ago I considered using this to measure the speed of the cars on a
> >track-car set my son had (he moved on to other things before that project got
> >far).
> >
> >I would also expect a very large variation between makes of motors, some
> >being
> >relatively "quiet," and motor load will also have a big affect.
> >
> >On a DC motor speed is often sensed by the back emf in a bridge circuit
> >arrangement, however this is an analog solution, and more difficult to get
> >high accuracy.
> >
> >Regards,
> >
> >Donald E Haselwood
> >
> >
> >
> >
> >On Saturday 18 June 2005 23:12, Peter Lissenburg wrote:
> > > Hi all,
> > > and sorry about this off topic, but I need the collective wisdom of
> > > the group. Is it OK, possible, wise, to use the noise spikes of the drive
> > > voltage of a DC motor to measure it's speed?
> > > Thanks for any guidance.
> > > Peter L.
> >
> >
> >
> >Yahoo! Groups Links
> >
> >
> >
>
(You need to be a member of 68hc12 -- send a blank email to 68hc12-subscribe@yahoogroups.com )
> Thanks guys,
> I'm looking at the CRO with a small motor running. I'm seeing
> bursts of spikes which get more numerous and spread over a longer burst as
> I increase the speed. Also I think I'm seeing asynchronous spikes as well.
> Maybe carbon build up or other dirt under the brush. Sounding a bit hit and
> miss, also with the variation between motors and load. This might not be
> worth following.
> I think it might be best to follow a more conventional line for the moment.
Excellent idea, most people go to great lenghts to suppress these for RFI reasons, apart from that the better the motor the lower these spikes and they are hard to separate from mains noise.
Measuring the back EMF is the normal cheap way, I do understand you want to do it on the cheap:-)
I used a switching method once and measured the EMF during the period the power was off (pulsed drive), that avoids getting errors from the drive current so you don't need to compensate, CMOS gate and a cap although in that particular case it was mainly to compensate for the very long cable runs.
Lastly if you use pancake motors drill a hole in the case where the wires bond on the edge, makes an excellent cheap tacho by counting these go past...
Don't forget a spinning motor packs a wallop of energy, do use lots of little resistors before getting too close to the CPU board:-)
Cheers
Theo
> At 12:25 AM 19/06/2005 -0400, you wrote:
> >Peter,
> >
> >Clearly, the spikes offer a way to very accurately measure the speed (e.g.
> >using an HC12 to measure the time between spikes). The key is where and how
> >does one pick up those noise spikes. The terminals of a DC motor driven by a
> >battery don't have much for spikes since the battery has such a low internal
> >impedance.
> >
> >The big voltage spike takes place on the armature winding that has just
> >broken
> >contact with the brushes. One might pick this up by stuffing a wire into the
> >motor to act as a capacitive pick up.
> >
> >The model airplanes that use electric motors usually have a by-pass cap right
> >at the motor terminals to reduce radio interference, so this suggests rf
> >pickup is another possibility.
> >
> >The current going into the motor does have a ripple. Some (actually many)
> >years ago I considered using this to measure the speed of the cars on a
> >track-car set my son had (he moved on to other things before that project got
> >far).
> >
> >I would also expect a very large variation between makes of motors, some
> >being
> >relatively "quiet," and motor load will also have a big affect.
> >
> >On a DC motor speed is often sensed by the back emf in a bridge circuit
> >arrangement, however this is an analog solution, and more difficult to get
> >high accuracy.
> >
> >Regards,
> >
> >Donald E Haselwood
> >
> >
> >
> >
> >On Saturday 18 June 2005 23:12, Peter Lissenburg wrote:
> > > Hi all,
> > > and sorry about this off topic, but I need the collective wisdom of
> > > the group. Is it OK, possible, wise, to use the noise spikes of the drive
> > > voltage of a DC motor to measure it's speed?
> > > Thanks for any guidance.
> > > Peter L.
> >
> >
> >
> >Yahoo! Groups Links
> >
> >
> >
>
(You need to be a member of 68hc12 -- send a blank email to 68hc12-subscribe@yahoogroups.com )
Re: OT; brushed DC motor speed measurement - theobee00 - Jun 20 6:20:00 2005
> --- In 68HC12@68HC..., Peter Lissenburg <peter@s...> wrote:
> > Thanks guys,
> > I'm looking at the CRO with a small motor running. I'm seeing
PS, Had a look a the pulse method described.
A few comments, firstly, using pulse methods will reduce brushlife and make lots of noise, look at the surpressor coils and snubbers used in SCR DC drives:-)
If you are using very small motors with pulse or tacho feedback, pure DC drive is best, only takes a bit of integrating of the pulse output from the CPU.
Bit more heat in the drive circuit.
Without such feedback you can still use the back EMF even when the motor is continously driven by means of IR feedback, this compensates for the voltage drop across the windngs etc.
Pretty well established techniques.
The CRO pictures show the drop quite well, he must have used a motor made with resistance wire... Cheers,
Theo
(You need to be a member of 68hc12 -- send a blank email to 68hc12-subscribe@yahoogroups.com )
> > Thanks guys,
> > I'm looking at the CRO with a small motor running. I'm seeing
PS, Had a look a the pulse method described.
A few comments, firstly, using pulse methods will reduce brushlife and make lots of noise, look at the surpressor coils and snubbers used in SCR DC drives:-)
If you are using very small motors with pulse or tacho feedback, pure DC drive is best, only takes a bit of integrating of the pulse output from the CPU.
Bit more heat in the drive circuit.
Without such feedback you can still use the back EMF even when the motor is continously driven by means of IR feedback, this compensates for the voltage drop across the windngs etc.
Pretty well established techniques.
The CRO pictures show the drop quite well, he must have used a motor made with resistance wire... Cheers,
Theo
(You need to be a member of 68hc12 -- send a blank email to 68hc12-subscribe@yahoogroups.com )
Re: OT: A/D noise on convert - Doron Fael - Jun 20 6:21:00 2005
James,
I believe I once read somewhere that when using a Ferrite Bead, it is not a
good idea to use many different values of capacitors. They were advising to
limit to only 2 capacitor values, or even just 1 capacitor value. Something
in the reaction between the different values of the different capacitors
may lead to resonance at some frequencies, which will actually amplify the
ripple, rather than attenuate it. You may try to remove the 6uF capacitor
or also the 22uF, and see if this helps reducing the ripple.
Another possibility is to make sure you use low-ESR capacitors, especially
for the 22uF and the 6uF capacitors that are likely Electrolithic, and tend
to have high ESR sometimes, especially if you choose one of the cheaper
caps that are available out there, rather than the more expensive low-ESR
caps. The high-ESR capacitors are usually associated with
relatively-speaking high inductance, which again may lead to resonance at
some specific frequencies, and may amplify rather than filter away the ripple.
Hope this helps,
Doron
Nohau
HC12 In-Circuit Emulators
www.nohau.com/emul12pc.html
At 14:47 19/06/2005 -0500, you wrote: >I've got a data card working with an HC12D60A. Connected to that card by
>some short wires (about 6" of #26 stranded) is a little daughter board with
>an MCP3002 A/D convertor. For the life of me, I can NOT keep noise off the
>Vdd line on the daughter board.
>
>I've got the Vdd run through a ferrite, then a 22 uF, 6 uF, and .1 cap -
>all with short leads to the MCP3002. Board has a good ground layer. I'm
>getting about 400 mV of noise on the Vdd line (measured directly between
>the ground plane and Vdd, right at the filter caps) coincident with the
>MCP3002 conversions. Now looking at the data sheet shows only about 5 ma.
>max load during conversion, and about .5 ma the rest of the time.
>
>Anyone run into something like this? A load of 5 ma just should NOT be
>having that kind of effect. [FWIW, the data line being converted is being
>fed from a different Vdd supply.]
>
> jmk
>
>-----------------------------------------------
>James M. Knox
>TriSoft ph 512-385-0316
>1300 Koenig Lane West fax 512-371-5716
>Suite 200
>Austin, Tx 78756 jknox@jkno...
>----------------------------------------------- [Non-text portions of this message have been removed]
(You need to be a member of 68hc12 -- send a blank email to 68hc12-subscribe@yahoogroups.com )
I believe I once read somewhere that when using a Ferrite Bead, it is not a
good idea to use many different values of capacitors. They were advising to
limit to only 2 capacitor values, or even just 1 capacitor value. Something
in the reaction between the different values of the different capacitors
may lead to resonance at some frequencies, which will actually amplify the
ripple, rather than attenuate it. You may try to remove the 6uF capacitor
or also the 22uF, and see if this helps reducing the ripple.
Another possibility is to make sure you use low-ESR capacitors, especially
for the 22uF and the 6uF capacitors that are likely Electrolithic, and tend
to have high ESR sometimes, especially if you choose one of the cheaper
caps that are available out there, rather than the more expensive low-ESR
caps. The high-ESR capacitors are usually associated with
relatively-speaking high inductance, which again may lead to resonance at
some specific frequencies, and may amplify rather than filter away the ripple.
Hope this helps,
Doron
Nohau
HC12 In-Circuit Emulators
www.nohau.com/emul12pc.html
At 14:47 19/06/2005 -0500, you wrote: >I've got a data card working with an HC12D60A. Connected to that card by
>some short wires (about 6" of #26 stranded) is a little daughter board with
>an MCP3002 A/D convertor. For the life of me, I can NOT keep noise off the
>Vdd line on the daughter board.
>
>I've got the Vdd run through a ferrite, then a 22 uF, 6 uF, and .1 cap -
>all with short leads to the MCP3002. Board has a good ground layer. I'm
>getting about 400 mV of noise on the Vdd line (measured directly between
>the ground plane and Vdd, right at the filter caps) coincident with the
>MCP3002 conversions. Now looking at the data sheet shows only about 5 ma.
>max load during conversion, and about .5 ma the rest of the time.
>
>Anyone run into something like this? A load of 5 ma just should NOT be
>having that kind of effect. [FWIW, the data line being converted is being
>fed from a different Vdd supply.]
>
> jmk
>
>-----------------------------------------------
>James M. Knox
>TriSoft ph 512-385-0316
>1300 Koenig Lane West fax 512-371-5716
>Suite 200
>Austin, Tx 78756 jknox@jkno...
>----------------------------------------------- [Non-text portions of this message have been removed]
(You need to be a member of 68hc12 -- send a blank email to 68hc12-subscribe@yahoogroups.com )
Re: Re: OT: A/D noise on convert - James M. Knox - Jun 20 19:34:00 2005
At 00:40 6/20/2005 +0000, you wrote:
> > getting about 400 mV of noise on the Vdd line
>
>Maybe the two VDD supplies are "bucking" each other. This would be
>most notable if there is a low impedance path between the + supply
>voltages. Perhaps you could try using just one of the supplies.
Good idea, but except for the ground plane, there is absolutely no
connection. The other supply goes straight to a resistive load. -----------------------------------------------
James M. Knox
TriSoft ph 512-385-0316
1300 Koenig Lane West fax 512-371-5716
Suite 200
Austin, Tx 78756 jknox@jkno...
-----------------------------------------------
(You need to be a member of 68hc12 -- send a blank email to 68hc12-subscribe@yahoogroups.com )
> > getting about 400 mV of noise on the Vdd line
>
>Maybe the two VDD supplies are "bucking" each other. This would be
>most notable if there is a low impedance path between the + supply
>voltages. Perhaps you could try using just one of the supplies.
Good idea, but except for the ground plane, there is absolutely no
connection. The other supply goes straight to a resistive load. -----------------------------------------------
James M. Knox
TriSoft ph 512-385-0316
1300 Koenig Lane West fax 512-371-5716
Suite 200
Austin, Tx 78756 jknox@jkno...
-----------------------------------------------
(You need to be a member of 68hc12 -- send a blank email to 68hc12-subscribe@yahoogroups.com )
Re: OT: A/D noise on convert - James M. Knox - Jun 20 19:38:00 2005
At 13:21 6/20/2005 +0300, you wrote:
>James,
>I believe I once read somewhere that when using a Ferrite Bead, it is not a
>good idea to use many different values of capacitors. They were advising to
>limit to only 2 capacitor values, or even just 1 capacitor value. Something
>in the reaction between the different values of the different capacitors
>may lead to resonance at some frequencies, which will actually amplify the
>ripple, rather than attenuate it. You may try to remove the 6uF capacitor
>or also the 22uF, and see if this helps reducing the ripple.
Interesting. Never heard of that, but certainly worth a try.
>Another possibility is to make sure you use low-ESR capacitors, especially
>for the 22uF and the 6uF capacitors that are likely Electrolithic, and tend
>to have high ESR sometimes, especially if you choose one of the cheaper
>caps that are available out there, rather than the more expensive low-ESR
>caps. The high-ESR capacitors are usually associated with
>relatively-speaking high inductance, which again may lead to resonance at
>some specific frequencies, and may amplify rather than filter away the ripple.
These are low-ESR tantalums, except for the very low value chip ceramics
(like the 47 pf's).
>Hope this helps,
Easy to try. Thanks for the suggestions. [I'm down to pretty much
shotgunning now.]
jmk -----------------------------------------------
James M. Knox
TriSoft ph 512-385-0316
1300 Koenig Lane West fax 512-371-5716
Suite 200
Austin, Tx 78756 jknox@jkno...
-----------------------------------------------
(You need to be a member of 68hc12 -- send a blank email to 68hc12-subscribe@yahoogroups.com )
>James,
>I believe I once read somewhere that when using a Ferrite Bead, it is not a
>good idea to use many different values of capacitors. They were advising to
>limit to only 2 capacitor values, or even just 1 capacitor value. Something
>in the reaction between the different values of the different capacitors
>may lead to resonance at some frequencies, which will actually amplify the
>ripple, rather than attenuate it. You may try to remove the 6uF capacitor
>or also the 22uF, and see if this helps reducing the ripple.
Interesting. Never heard of that, but certainly worth a try.
>Another possibility is to make sure you use low-ESR capacitors, especially
>for the 22uF and the 6uF capacitors that are likely Electrolithic, and tend
>to have high ESR sometimes, especially if you choose one of the cheaper
>caps that are available out there, rather than the more expensive low-ESR
>caps. The high-ESR capacitors are usually associated with
>relatively-speaking high inductance, which again may lead to resonance at
>some specific frequencies, and may amplify rather than filter away the ripple.
These are low-ESR tantalums, except for the very low value chip ceramics
(like the 47 pf's).
>Hope this helps,
Easy to try. Thanks for the suggestions. [I'm down to pretty much
shotgunning now.]
jmk -----------------------------------------------
James M. Knox
TriSoft ph 512-385-0316
1300 Koenig Lane West fax 512-371-5716
Suite 200
Austin, Tx 78756 jknox@jkno...
-----------------------------------------------
(You need to be a member of 68hc12 -- send a blank email to 68hc12-subscribe@yahoogroups.com )
Re: OT: A/D noise on convert - Steve Russell - Jun 20 22:18:00 2005
How about noise coming in via the scope probe ground?
Do the ADC readings show the same noise without the scope connected?
If yes:
Could the noise really be caused by currents in the scope probe shield, and
scope equipment ground pin?
Try Isolating the scope or using a differential probe.
Steve Russell
Nohau At 12:47 PM 6/19/2005, "James M. Knox" <jknox@jkno...> wrote: >I've got a data card working with an HC12D60A. Connected to that card by
>some short wires (about 6" of #26 stranded) is a little daughter board with
>an MCP3002 A/D convertor. For the life of me, I can NOT keep noise off the
>Vdd line on the daughter board.
>
>I've got the Vdd run through a ferrite, then a 22 uF, 6 uF, and .1 cap -
>all with short leads to the MCP3002. Board has a good ground layer. I'm
>getting about 400 mV of noise on the Vdd line (measured directly between
>the ground plane and Vdd, right at the filter caps) coincident with the
>MCP3002 conversions. Now looking at the data sheet shows only about 5 ma.
>max load during conversion, and about .5 ma the rest of the time.
>
>Anyone run into something like this? A load of 5 ma just should NOT be
>having that kind of effect. [FWIW, the data line being converted is being
>fed from a different Vdd supply.]
>
> jmk
>
>-----------------------------------------------
>James M. Knox
>TriSoft ph 512-385-0316
>1300 Koenig Lane West fax 512-371-5716
>Suite 200
>Austin, Tx 78756 jknox@jkno...
>----------------------------------------------- >
>
>Yahoo! Groups Links
(You need to be a member of 68hc12 -- send a blank email to 68hc12-subscribe@yahoogroups.com )
Do the ADC readings show the same noise without the scope connected?
If yes:
Could the noise really be caused by currents in the scope probe shield, and
scope equipment ground pin?
Try Isolating the scope or using a differential probe.
Steve Russell
Nohau At 12:47 PM 6/19/2005, "James M. Knox" <jknox@jkno...> wrote: >I've got a data card working with an HC12D60A. Connected to that card by
>some short wires (about 6" of #26 stranded) is a little daughter board with
>an MCP3002 A/D convertor. For the life of me, I can NOT keep noise off the
>Vdd line on the daughter board.
>
>I've got the Vdd run through a ferrite, then a 22 uF, 6 uF, and .1 cap -
>all with short leads to the MCP3002. Board has a good ground layer. I'm
>getting about 400 mV of noise on the Vdd line (measured directly between
>the ground plane and Vdd, right at the filter caps) coincident with the
>MCP3002 conversions. Now looking at the data sheet shows only about 5 ma.
>max load during conversion, and about .5 ma the rest of the time.
>
>Anyone run into something like this? A load of 5 ma just should NOT be
>having that kind of effect. [FWIW, the data line being converted is being
>fed from a different Vdd supply.]
>
> jmk
>
>-----------------------------------------------
>James M. Knox
>TriSoft ph 512-385-0316
>1300 Koenig Lane West fax 512-371-5716
>Suite 200
>Austin, Tx 78756 jknox@jkno...
>----------------------------------------------- >
>
>Yahoo! Groups Links
(You need to be a member of 68hc12 -- send a blank email to 68hc12-subscribe@yahoogroups.com )
Re: OT: A/D noise on convert - Stephen Trier - Jun 21 11:29:00 2005
James,
Have you tried removing the Vdd ferrite? 400 mV at 5 mA is about 80
ohms of impedance, which could come from the ferrite bead. The ferrite
will reduce the amount of EMI the board sends out the power supply wire,
but by increasing the impedance on the power supply line, it won't help
with the power supply bounce you're seeing.
Stephen
--
Stephen Trier
Technical Development Lab
Cleveland FES Center
sct@sct@...
(You need to be a member of 68hc12 -- send a blank email to 68hc12-subscribe@yahoogroups.com )
Have you tried removing the Vdd ferrite? 400 mV at 5 mA is about 80
ohms of impedance, which could come from the ferrite bead. The ferrite
will reduce the amount of EMI the board sends out the power supply wire,
but by increasing the impedance on the power supply line, it won't help
with the power supply bounce you're seeing.
Stephen
--
Stephen Trier
Technical Development Lab
Cleveland FES Center
sct@sct@...
(You need to be a member of 68hc12 -- send a blank email to 68hc12-subscribe@yahoogroups.com )
Re: OT: A/D noise on convert - zeta_alpha2002 - Jun 21 16:58:00 2005
> Anyone run into something like this? A load of 5 ma just should NOT be
> having that kind of effect.
I encountered similar problem before. Maynot exactly the same as
yours but symptom is familiar with noise during analysis. Instead of
noise on VDD, I saw it on ground. This happened I was using National
Instrument DAQ.
Add a series 1k to 10k from source to MCP3002 A/D convertor input pin.
Try that and see what happens.
(You need to be a member of 68hc12 -- send a blank email to 68hc12-subscribe@yahoogroups.com )
> having that kind of effect.
I encountered similar problem before. Maynot exactly the same as
yours but symptom is familiar with noise during analysis. Instead of
noise on VDD, I saw it on ground. This happened I was using National
Instrument DAQ.
Add a series 1k to 10k from source to MCP3002 A/D convertor input pin.
Try that and see what happens.
(You need to be a member of 68hc12 -- send a blank email to 68hc12-subscribe@yahoogroups.com )
Re: OT: A/D noise on convert - James M. Knox - Jun 21 21:39:00 2005
At 11:29 6/21/2005 -0400, you wrote:
>James,
>
>Have you tried removing the Vdd ferrite? 400 mV at 5 mA is about 80
>ohms of impedance, which could come from the ferrite bead. The ferrite
>will reduce the amount of EMI the board sends out the power supply wire,
>but by increasing the impedance on the power supply line, it won't help
>with the power supply bounce you're seeing.
Hmmm... Now that's an interesting theory. The little SMD ferrites I picked
have a fairly low DC resistance (don't recall how low at the moment), and
so directly that's probably not the problem. However, with a sudden
current change the ferrite will act like a much higher resistance
(inductance). Now I was thinking that:
a) The capacitance was high enough to cover power over that ramp period,
b) Any spikes cause by this should be a lot shorter than I am seeing.
[Note: It's not uncommon to generate a low current isolated power source
from Vdd by adding a series resistor, followed by a larger capacitor.]
Still, your idea that I may have shot myself in the foot (so to speak) is
worth checking out. Easy enough to jumper the ferrite for a test. [And
about the only thing I haven't tried yet.]
jmk -----------------------------------------------
James M. Knox
TriSoft ph 512-385-0316
1300 Koenig Lane West fax 512-371-5716
Suite 200
Austin, Tx 78756 jknox@jkno...
-----------------------------------------------
(You need to be a member of 68hc12 -- send a blank email to 68hc12-subscribe@yahoogroups.com )
>James,
>
>Have you tried removing the Vdd ferrite? 400 mV at 5 mA is about 80
>ohms of impedance, which could come from the ferrite bead. The ferrite
>will reduce the amount of EMI the board sends out the power supply wire,
>but by increasing the impedance on the power supply line, it won't help
>with the power supply bounce you're seeing.
Hmmm... Now that's an interesting theory. The little SMD ferrites I picked
have a fairly low DC resistance (don't recall how low at the moment), and
so directly that's probably not the problem. However, with a sudden
current change the ferrite will act like a much higher resistance
(inductance). Now I was thinking that:
a) The capacitance was high enough to cover power over that ramp period,
b) Any spikes cause by this should be a lot shorter than I am seeing.
[Note: It's not uncommon to generate a low current isolated power source
from Vdd by adding a series resistor, followed by a larger capacitor.]
Still, your idea that I may have shot myself in the foot (so to speak) is
worth checking out. Easy enough to jumper the ferrite for a test. [And
about the only thing I haven't tried yet.]
jmk -----------------------------------------------
James M. Knox
TriSoft ph 512-385-0316
1300 Koenig Lane West fax 512-371-5716
Suite 200
Austin, Tx 78756 jknox@jkno...
-----------------------------------------------
(You need to be a member of 68hc12 -- send a blank email to 68hc12-subscribe@yahoogroups.com )
Re: Re: OT: A/D noise on convert - James M. Knox - Jun 21 21:43:00 2005
At 20:58 6/21/2005 +0000, you wrote:
> > Anyone run into something like this? A load of 5 ma just should NOT be
> > having that kind of effect.
>
>I encountered similar problem before. Maynot exactly the same as
>yours but symptom is familiar with noise during analysis. Instead of
>noise on VDD, I saw it on ground. This happened I was using National
>Instrument DAQ.
>
>Add a series 1k to 10k from source to MCP3002 A/D convertor input pin.
> Try that and see what happens.
Hmmm... I was thinking that the noise was being caused by the MCP3002,
because it clearly relates to the conversion process. What you are
suggesting is that it really may be the low-impedance op-amp feeding
MCP3002 that's indirectly causing the problem. The MCP3002 starts a
conversion, effectively grounding out the output of the op amp, causing it
to draw more power, causing noise on the power lines.
The series resistance will necessitate slowing down the conversions (have
to see if the 3002 allows that), but will be worth it if it gives me a few
more bits of accuracy.
jmk -----------------------------------------------
James M. Knox
TriSoft ph 512-385-0316
1300 Koenig Lane West fax 512-371-5716
Suite 200
Austin, Tx 78756 jknox@jkno...
-----------------------------------------------
(You need to be a member of 68hc12 -- send a blank email to 68hc12-subscribe@yahoogroups.com )
> > Anyone run into something like this? A load of 5 ma just should NOT be
> > having that kind of effect.
>
>I encountered similar problem before. Maynot exactly the same as
>yours but symptom is familiar with noise during analysis. Instead of
>noise on VDD, I saw it on ground. This happened I was using National
>Instrument DAQ.
>
>Add a series 1k to 10k from source to MCP3002 A/D convertor input pin.
> Try that and see what happens.
Hmmm... I was thinking that the noise was being caused by the MCP3002,
because it clearly relates to the conversion process. What you are
suggesting is that it really may be the low-impedance op-amp feeding
MCP3002 that's indirectly causing the problem. The MCP3002 starts a
conversion, effectively grounding out the output of the op amp, causing it
to draw more power, causing noise on the power lines.
The series resistance will necessitate slowing down the conversions (have
to see if the 3002 allows that), but will be worth it if it gives me a few
more bits of accuracy.
jmk -----------------------------------------------
James M. Knox
TriSoft ph 512-385-0316
1300 Koenig Lane West fax 512-371-5716
Suite 200
Austin, Tx 78756 jknox@jkno...
-----------------------------------------------
(You need to be a member of 68hc12 -- send a blank email to 68hc12-subscribe@yahoogroups.com )
Re: OT: A/D noise on convert - zeta_alpha2002 - Jun 22 8:30:00 2005
> The series resistance will necessitate slowing down the conversions
(have
> to see if the 3002 allows that), but will be worth it if it gives me
a few
> more bits of accuracy.
I must say if that all of the advice given does not work out, maybe
the MCP3002 you are currently working with is toast or flawed. Try a
new MCP3002. Perhaps you've tried that already?
--- In 68HC12@68HC..., "James M. Knox" <jknox@t...> wrote:
> At 20:58 6/21/2005 +0000, you wrote:
> > > Anyone run into something like this? A load of 5 ma just should
NOT be
> > > having that kind of effect.
> >
> >I encountered similar problem before. Maynot exactly the same as
> >yours but symptom is familiar with noise during analysis. Instead of
> >noise on VDD, I saw it on ground. This happened I was using National
> >Instrument DAQ.
> >
> >Add a series 1k to 10k from source to MCP3002 A/D convertor input pin.
> > Try that and see what happens.
>
> Hmmm... I was thinking that the noise was being caused by the MCP3002,
> because it clearly relates to the conversion process. What you are
> suggesting is that it really may be the low-impedance op-amp feeding
> MCP3002 that's indirectly causing the problem. The MCP3002 starts a
> conversion, effectively grounding out the output of the op amp,
causing it
> to draw more power, causing noise on the power lines.
>
> The series resistance will necessitate slowing down the conversions
(have
> to see if the 3002 allows that), but will be worth it if it gives me
a few
> more bits of accuracy.
>
> jmk > -----------------------------------------------
> James M. Knox
> TriSoft ph 512-385-0316
> 1300 Koenig Lane West fax 512-371-5716
> Suite 200
> Austin, Tx 78756 jknox@t...
> -----------------------------------------------
(You need to be a member of 68hc12 -- send a blank email to 68hc12-subscribe@yahoogroups.com )
(have
> to see if the 3002 allows that), but will be worth it if it gives me
a few
> more bits of accuracy.
I must say if that all of the advice given does not work out, maybe
the MCP3002 you are currently working with is toast or flawed. Try a
new MCP3002. Perhaps you've tried that already?
--- In 68HC12@68HC..., "James M. Knox" <jknox@t...> wrote:
> At 20:58 6/21/2005 +0000, you wrote:
> > > Anyone run into something like this? A load of 5 ma just should
NOT be
> > > having that kind of effect.
> >
> >I encountered similar problem before. Maynot exactly the same as
> >yours but symptom is familiar with noise during analysis. Instead of
> >noise on VDD, I saw it on ground. This happened I was using National
> >Instrument DAQ.
> >
> >Add a series 1k to 10k from source to MCP3002 A/D convertor input pin.
> > Try that and see what happens.
>
> Hmmm... I was thinking that the noise was being caused by the MCP3002,
> because it clearly relates to the conversion process. What you are
> suggesting is that it really may be the low-impedance op-amp feeding
> MCP3002 that's indirectly causing the problem. The MCP3002 starts a
> conversion, effectively grounding out the output of the op amp,
causing it
> to draw more power, causing noise on the power lines.
>
> The series resistance will necessitate slowing down the conversions
(have
> to see if the 3002 allows that), but will be worth it if it gives me
a few
> more bits of accuracy.
>
> jmk > -----------------------------------------------
> James M. Knox
> TriSoft ph 512-385-0316
> 1300 Koenig Lane West fax 512-371-5716
> Suite 200
> Austin, Tx 78756 jknox@t...
> -----------------------------------------------
(You need to be a member of 68hc12 -- send a blank email to 68hc12-subscribe@yahoogroups.com )
RE: Re: OT: A/D noise on convert - Mark Wyman - Jun 22 9:19:00 2005
If you have narrowed it down to the MPC3002, put another ferrite in series
and ceramic 10uF chip cap + 0.1uF chip cap as close as you can to the power
pins of just this device. This will source a large current spike to the
device, meanwhile preventing the spike from reflecting to the rest of the
power supply. It makes me wonder that if you are seeing this spike during
conversion that your conversion results must be far off. Also make sure your
grounds are very solid, and in the case of devices with high current spike,
do not use thermals on the ground planes unless absolutely necessary.
The ceramic chip caps I find are even better than tantalum capacitors as
they tend to be more obtainable with similar prices and equivalent or lower
ESRs, not to mention they are bipolar, so you don't wind up with foul
smelling smoke. ;-).
Something else to consider: The ground lead of most scope probes are long,
and act very much like an antenna, not giving you a true ground. It is
difficult at best to measure noise with a long ground lead. To quickly
confirm it is not your ground lead, touch the probe tip to the ground lead
connection on your board and see if the noise goes away. If it does not, you
are picking up RFI radiated from your board and no amount of filtering, only
shielding, will help with reducing noise measurements.
Someone else mentioned using a differential probe, this is an excellent
idea. Another idea is to get one of those short spring-clip grounds that is
just about the length of the tip.
-Mark
_____
From: 68HC12@68HC... [mailto:68HC12@68HC...] On Behalf Of
zeta_alpha2002
Sent: Wednesday, June 22, 2005 8:31 AM
To: 68HC12@68HC...
Subject: [68HC12] Re: OT: A/D noise on convert
> The series resistance will necessitate slowing down the conversions
(have
> to see if the 3002 allows that), but will be worth it if it gives me
a few
> more bits of accuracy.
I must say if that all of the advice given does not work out, maybe
the MCP3002 you are currently working with is toast or flawed. Try a
new MCP3002. Perhaps you've tried that already?
--- In 68HC12@68HC..., "James M. Knox" <jknox@t...> wrote:
> At 20:58 6/21/2005 +0000, you wrote:
> > > Anyone run into something like this? A load of 5 ma just should
NOT be
> > > having that kind of effect.
> >
> >I encountered similar problem before. Maynot exactly the same as
> >yours but symptom is familiar with noise during analysis. Instead of
> >noise on VDD, I saw it on ground. This happened I was using National
> >Instrument DAQ.
> >
> >Add a series 1k to 10k from source to MCP3002 A/D convertor input pin.
> > Try that and see what happens.
>
> Hmmm... I was thinking that the noise was being caused by the MCP3002,
> because it clearly relates to the conversion process. What you are
> suggesting is that it really may be the low-impedance op-amp feeding
> MCP3002 that's indirectly causing the problem. The MCP3002 starts a
> conversion, effectively grounding out the output of the op amp,
causing it
> to draw more power, causing noise on the power lines.
>
> The series resistance will necessitate slowing down the conversions
(have
> to see if the 3002 allows that), but will be worth it if it gives me
a few
> more bits of accuracy.
>
> jmk > -----------------------------------------------
> James M. Knox
> TriSoft ph 512-385-0316
> 1300 Koenig Lane West fax 512-371-5716
> Suite 200
> Austin, Tx 78756 jknox@t...
> ----------------------------------------------- _____
> Terms of Service.
[Non-text portions of this message have been removed]
(You need to be a member of 68hc12 -- send a blank email to 68hc12-subscribe@yahoogroups.com )
and ceramic 10uF chip cap + 0.1uF chip cap as close as you can to the power
pins of just this device. This will source a large current spike to the
device, meanwhile preventing the spike from reflecting to the rest of the
power supply. It makes me wonder that if you are seeing this spike during
conversion that your conversion results must be far off. Also make sure your
grounds are very solid, and in the case of devices with high current spike,
do not use thermals on the ground planes unless absolutely necessary.
The ceramic chip caps I find are even better than tantalum capacitors as
they tend to be more obtainable with similar prices and equivalent or lower
ESRs, not to mention they are bipolar, so you don't wind up with foul
smelling smoke. ;-).
Something else to consider: The ground lead of most scope probes are long,
and act very much like an antenna, not giving you a true ground. It is
difficult at best to measure noise with a long ground lead. To quickly
confirm it is not your ground lead, touch the probe tip to the ground lead
connection on your board and see if the noise goes away. If it does not, you
are picking up RFI radiated from your board and no amount of filtering, only
shielding, will help with reducing noise measurements.
Someone else mentioned using a differential probe, this is an excellent
idea. Another idea is to get one of those short spring-clip grounds that is
just about the length of the tip.
-Mark
_____
From: 68HC12@68HC... [mailto:68HC12@68HC...] On Behalf Of
zeta_alpha2002
Sent: Wednesday, June 22, 2005 8:31 AM
To: 68HC12@68HC...
Subject: [68HC12] Re: OT: A/D noise on convert
> The series resistance will necessitate slowing down the conversions
(have
> to see if the 3002 allows that), but will be worth it if it gives me
a few
> more bits of accuracy.
I must say if that all of the advice given does not work out, maybe
the MCP3002 you are currently working with is toast or flawed. Try a
new MCP3002. Perhaps you've tried that already?
--- In 68HC12@68HC..., "James M. Knox" <jknox@t...> wrote:
> At 20:58 6/21/2005 +0000, you wrote:
> > > Anyone run into something like this? A load of 5 ma just should
NOT be
> > > having that kind of effect.
> >
> >I encountered similar problem before. Maynot exactly the same as
> >yours but symptom is familiar with noise during analysis. Instead of
> >noise on VDD, I saw it on ground. This happened I was using National
> >Instrument DAQ.
> >
> >Add a series 1k to 10k from source to MCP3002 A/D convertor input pin.
> > Try that and see what happens.
>
> Hmmm... I was thinking that the noise was being caused by the MCP3002,
> because it clearly relates to the conversion process. What you are
> suggesting is that it really may be the low-impedance op-amp feeding
> MCP3002 that's indirectly causing the problem. The MCP3002 starts a
> conversion, effectively grounding out the output of the op amp,
causing it
> to draw more power, causing noise on the power lines.
>
> The series resistance will necessitate slowing down the conversions
(have
> to see if the 3002 allows that), but will be worth it if it gives me
a few
> more bits of accuracy.
>
> jmk > -----------------------------------------------
> James M. Knox
> TriSoft ph 512-385-0316
> 1300 Koenig Lane West fax 512-371-5716
> Suite 200
> Austin, Tx 78756 jknox@t...
> ----------------------------------------------- _____
> Terms of Service.
[Non-text portions of this message have been removed]
(You need to be a member of 68hc12 -- send a blank email to 68hc12-subscribe@yahoogroups.com )
Re: OT: A/D noise on convert - Stephen Trier - Jun 22 16:42:00 2005
On Tue, Jun 21, 2005 at 08:39:23PM -0500, James M. Knox wrote:
> a) The capacitance was high enough to cover power over that ramp period,
> b) Any spikes cause by this should be a lot shorter than I am seeing.
Um, yeah. I was trying to ignore the capacitance, because it ruins my
pretty little theory. :-)
Stephen
--
Stephen Trier
Technical Development Lab
Cleveland FES Center
sct@sct@...
(You need to be a member of 68hc12 -- send a blank email to 68hc12-subscribe@yahoogroups.com )
> a) The capacitance was high enough to cover power over that ramp period,
> b) Any spikes cause by this should be a lot shorter than I am seeing.
Um, yeah. I was trying to ignore the capacitance, because it ruins my
pretty little theory. :-)
Stephen
--
Stephen Trier
Technical Development Lab
Cleveland FES Center
sct@sct@...
(You need to be a member of 68hc12 -- send a blank email to 68hc12-subscribe@yahoogroups.com )
Re: Re: OT: A/D noise on convert - James M. Knox - Jun 22 20:33:00 2005
At 12:30 6/22/2005 +0000, you wrote:
> > The series resistance will necessitate slowing down the conversions
>(have
> > to see if the 3002 allows that), but will be worth it if it gives me
>a few
> > more bits of accuracy.
>
>I must say if that all of the advice given does not work out, maybe
>the MCP3002 you are currently working with is toast or flawed. Try a
>new MCP3002. Perhaps you've tried that already?
Haven't tried a new one, but this one certainly seems to be converting just
fine (at least given the noise). Doesn't act damaged... but if all else
fails... <G -----------------------------------------------
James M. Knox
TriSoft ph 512-385-0316
1300 Koenig Lane West fax 512-371-5716
Suite 200
Austin, Tx 78756 jknox@jkno...
-----------------------------------------------
(You need to be a member of 68hc12 -- send a blank email to 68hc12-subscribe@yahoogroups.com )
> > The series resistance will necessitate slowing down the conversions
>(have
> > to see if the 3002 allows that), but will be worth it if it gives me
>a few
> > more bits of accuracy.
>
>I must say if that all of the advice given does not work out, maybe
>the MCP3002 you are currently working with is toast or flawed. Try a
>new MCP3002. Perhaps you've tried that already?
Haven't tried a new one, but this one certainly seems to be converting just
fine (at least given the noise). Doesn't act damaged... but if all else
fails... <G -----------------------------------------------
James M. Knox
TriSoft ph 512-385-0316
1300 Koenig Lane West fax 512-371-5716
Suite 200
Austin, Tx 78756 jknox@jkno...
-----------------------------------------------
(You need to be a member of 68hc12 -- send a blank email to 68hc12-subscribe@yahoogroups.com )