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Hi,

I have created an interface circuit for breadboarding to save time
rebuilding the same circuit each time I need it. The circuit contains a
regulated 5V power supply and a highly configurable RS-232 interface.
Check it out on my projects page:
http://home.austin.rr.com/perks/basicx/Projects/ . Comments are welcome.

Mike





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--- In basicx@basi..., Mike Perks <basicx@a...> wrote:
> Hi,
>
> I have created an interface circuit for breadboarding to save time
> rebuilding the same circuit each time I need it. The circuit
contains a
> regulated 5V power supply and a highly configurable RS-232
interface.
> Check it out on my projects page:
> http://home.austin.rr.com/perks/basicx/Projects/ . Comments are
welcome.
>
> Mike

Hey, that is beautiful. If you make some actual PCBs, I would buy one!

Do you think that the 470uF cap on the input is enough? I do not know
the answer, just asking. When I assemble my breadboard regulators, I
usually end up with 1000 - 2200uF, just because "bigger is better",
and more expensive and BIGGER.

If 470 is fine, it would save me some real estate in a circuit I am
designing right now.

Also, you only have an electrolytic (I think) on the output.
Shouldn't there be a small ceramic there too?

Today I was working with my circuit and had just installed a
decoupling cap on an IC. I only had tiny ceramic caps, and big
electrolytics except for a couple of 10uF tantalums. I used one of
the tantalums. Still did not stop the glitching. Then a few minutes
later I heard Pfffff-T. And smoke started pouring out of my enclosure.

Well, it would appear that I am pretty stupid. I did not know that
tantalums are polarized, and of course I had it reversed. THe cap was
rated for 16vdc, and I was only using 5... Pretty impressive!!!

-Tony




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arhodes19044 wrote:

> --- In basicx@basi..., Mike Perks <basicx@a...> wrote:
> > Hi,
> >
> > I have created an interface circuit for breadboarding to save time
> > rebuilding the same circuit each time I need it. The circuit
> contains a
> > regulated 5V power supply and a highly configurable RS-232
> interface.
> > Check it out on my projects page:
> > http://home.austin.rr.com/perks/basicx/Projects/ . Comments are
> welcome.
> >
> > Mike
>
> Hey, that is beautiful. If you make some actual PCBs, I would buy one!

Thanks. Does it have to be a PCB? I have a stripboard based one I'm
selling for $40 ;) > Do you think that the 470uF cap on the input is enough? I do not know
> the answer, just asking. When I assemble my breadboard regulators, I
> usually end up with 1000 - 2200uF, just because "bigger is better",
> and more expensive and BIGGER.
>
> If 470 is fine, it would save me some real estate in a circuit I am
> designing right now.

I think it depends on how bad or good the supply is. I think you are
right about upping it to at least 1000uF. > Also, you only have an electrolytic (I think) on the output.
> Shouldn't there be a small ceramic there too?

It is very cleverly hidden. C6 is the output 0.1uF cap. I have redrawn
that part of the schematic so it is easier to see. > Today I was working with my circuit and had just installed a
> decoupling cap on an IC. I only had tiny ceramic caps, and big
> electrolytics except for a couple of 10uF tantalums. I used one of
> the tantalums. Still did not stop the glitching. Then a few minutes
> later I heard Pfffff-T. And smoke started pouring out of my enclosure.
>
> Well, it would appear that I am pretty stupid. I did not know that
> tantalums are polarized, and of course I had it reversed. THe cap was
> rated for 16vdc, and I was only using 5... Pretty impressive!!!

Luckily it was only a few cheap caps :)

Regards,
Mike



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Mike, you are 'dangerous' with hardware ;-) Seriously, this is good
work and well 'thought-out'. Especially the serial interface.
However, You really don't need the big electrolytics on the
regulator. No matter how badly the 'Wallwart' output is, the
recommended 0.33uf cap is fine. I normally use a 1uf Tantalum rated
at least 30V as 'Wallwart's output can vary all over the place
depending on load... It's good you added D2 for reverse polarity
prevention. I can't see a need for D1 in this application. I also see
no need for the 0.1uf cap on the input. On the output side, I would
use a 0.1uf monolithic cap with a 10uf tantalum. SW1 is a good idea
for external supplies, especially 3.3V logic which the BX-24P
supports. However, you may want to implement that with jumpers
instead of a switch. Speaking of switches, I would would add one to
the raw supply input.

- Tom

--- In basicx@basi..., Mike Perks <basicx@a...> wrote:
> Hi,
>
> I have created an interface circuit for breadboarding to save time
> rebuilding the same circuit each time I need it. The circuit
contains a
> regulated 5V power supply and a highly configurable RS-232
interface.
> Check it out on my projects page:
> http://home.austin.rr.com/perks/basicx/Projects/ . Comments are
welcome.
>
> Mike




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tombhandley wrote:

> Mike, you are 'dangerous' with hardware ;-) Seriously, this is good
> work and well 'thought-out'. Especially the serial interface.

Thank you. I'm still trying to figure out this 'hardware' stuff.

> However, You really don't need the big electrolytics on the
> regulator. No matter how badly the 'Wallwart' output is, the
> recommended 0.33uf cap is fine. I normally use a 1uf Tantalum rated
> at least 30V as 'Wallwart's output can vary all over the place

I added C7 (1000uF) in case there was a lot of supply ripple. Are you
saying that this isn't normally the case so I can safely remove it and
replace the 0.1uF with a 1uF tantulum?

> depending on load... It's good you added D2 for reverse polarity
> prevention. I can't see a need for D1 in this application. I also see
> no need for the 0.1uf cap on the input. On the output side, I would

Everyone seems to have different ideas on what makes a good design for
power supplies, particularly for the capacitors needed by regulators. I
wonder if there is a definitive source anywhere? I added D1 as
additional protection although I have also read that modern regulators
don't need one. > use a 0.1uf monolithic cap with a 10uf tantalum. SW1 is a good idea
> for external supplies, especially 3.3V logic which the BX-24P
> supports. However, you may want to implement that with jumpers
> instead of a switch. Speaking of switches, I would would add one to
> the raw supply input.

Is this because current still flows through the regulator even with SW1
is in the off position?

Regards,
Mike





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--- In basicx@basi..., Mike Perks <basicx@a...> wrote:
> I added C7 (1000uF) in case there was a lot of supply ripple. Are
> you saying that this isn't normally the case so I can safely
> remove it and replace the 0.1uF with a 1uF tantulum?

The small ceramic capacitors (0.01uF to 0.1uF) serve a different
purpose than the bulk capacitance (electrolytic or tantalum).
[Actually, tantalum caps are electrolytic, too but if you refer to
an electolytic cap most engineers assume that you're referring to an
aluminum electrolytic.]

The small caps are usually distributed around the board to absorb
switching spikes. Because they have a lower ESR (effective series
resistance) than the bulk capacitors they are better at damping high
frequency noise, spikes etc. That's why you often see a small
ceramic in parallel with a larger electrolytic.

Tantalums generally are more expensive, have a higher capacitance to
volume ratio and a lower ESR but are less forgiving of reverse
voltages and over-voltage spikes all as compared to aluminum
electrolytics.





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Mike, Don earlier mentioned electrolytic and tantalum caps. As he
said, tantalum caps are more expensive but are much smaller and have
a lower ESR. They really can 'explode' if 'abused' but you have
reverse polarity protection and you have to 'draw a line' on your
target audience. If somone connects a 48V supply to it, there are
going to be 'fireworks'...

Taking another look at SW1, folks can easily add a 3.3V supply there
since the regulator is disconnected. My mistake...

C7 is not normally needed in high ripple conditions. This depends on
the regulator so you need to take a close look at the manufacture's
data sheet and the Ripple Rejection spec. The best thing to do is
start with the manufacture's reference design and read the 'fine
print' in the data sheet. You are right about the many opinions about
regulator caps. I tend to go with recommended values based on my
input supply, load, and experience over the years. Most cheap
unregulated 'Wallwarts' already have a big electrolytic cap on the
output.

D1 is really not needed with current generation regulators and
smaller caps.

- Tom

--- In basicx@basi..., Mike Perks <basicx@a...> wrote:
> tombhandley wrote:
>
> > Mike, you are 'dangerous' with hardware ;-) Seriously, this is
good
> > work and well 'thought-out'. Especially the serial interface.
>
> Thank you. I'm still trying to figure out this 'hardware' stuff.
>
> > However, You really don't need the big electrolytics on the
> > regulator. No matter how badly the 'Wallwart' output is, the
> > recommended 0.33uf cap is fine. I normally use a 1uf Tantalum
rated
> > at least 30V as 'Wallwart's output can vary all over the place
>
> I added C7 (1000uF) in case there was a lot of supply ripple. Are
you
> saying that this isn't normally the case so I can safely remove it
and
> replace the 0.1uF with a 1uF tantulum?
>
> > depending on load... It's good you added D2 for reverse polarity
> > prevention. I can't see a need for D1 in this application. I also
see
> > no need for the 0.1uf cap on the input. On the output side, I
would
>
> Everyone seems to have different ideas on what makes a good design
for
> power supplies, particularly for the capacitors needed by
regulators. I
> wonder if there is a definitive source anywhere? I added D1 as
> additional protection although I have also read that modern
regulators
> don't need one.
>
> >
> > use a 0.1uf monolithic cap with a 10uf tantalum. SW1 is a good
idea
> > for external supplies, especially 3.3V logic which the BX-24P
> > supports. However, you may want to implement that with jumpers
> > instead of a switch. Speaking of switches, I would would add one
to
> > the raw supply input.
>
> Is this because current still flows through the regulator even with
SW1
> is in the off position?
>
> Regards,
> Mike




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tombhandley wrote:

Good help from you and Don. I'm aware of the ESR difference between
Tantulum and Aluminium as I have had a need to use them before. But I
never knew you could blow up tantulums so easily. I did once accidently
connect an aluminium electrolytic the wrong way around for a second but
thankfully nothing bad happened.

> Mike, Don earlier mentioned electrolytic and tantalum caps. As he
> said, tantalum caps are more expensive but are much smaller and have
> a lower ESR. They really can 'explode' if 'abused' but you have
> reverse polarity protection and you have to 'draw a line' on your
> target audience. If somone connects a 48V supply to it, there are
> going to be 'fireworks'...
>
> Taking another look at SW1, folks can easily add a 3.3V supply there
> since the regulator is disconnected. My mistake...
>
> C7 is not normally needed in high ripple conditions. This depends on
> the regulator so you need to take a close look at the manufacture's
> data sheet and the Ripple Rejection spec. The best thing to do is
> start with the manufacture's reference design and read the 'fine
> print' in the data sheet. You are right about the many opinions about
> regulator caps. I tend to go with recommended values based on my
> input supply, load, and experience over the years. Most cheap
> unregulated 'Wallwarts' already have a big electrolytic cap on the
> output.

> D1 is really not needed with current generation regulators and
> smaller caps.

I added D1 for safety reasons as I saw it on some other regulator
circuits. No harm in adding a 4 cent diode, I guess.

Regards,
Mike





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--- In basicx@basi..., Mike Perks <basicx@a...> wrote:
> I added D1 for safety reasons as I saw it on some other regulator
> circuits. No harm in adding a 4 cent diode, I guess.

The purpose of the diode is to avoid having a too-large current flow
back into the output stage of the regulator under certain (unusual)
conditions.

As Tom indicated, whether it is required or not depends on the
particular regulator and the details of your circuit. The datasheet
will indicate when it is required. For example, the datasheet for the
older LM150/LM350 series says "For output capacitors less than 25uF
there is no need to use [the diode]".

Of course, having it and not needing it is better than needing it and
not having it.





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> http://home.austin.rr.com/perks/basicx/Projects/

Mike, what produced those beautiful virtual board images? Tom
Tom Becker
--... ...--
GTBecker@GTBe... www.RighTime.com
The RighTime Clock Company, Inc., Cape Coral, Florida USA
+1239 540 5700



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Tom Becker wrote:

> > http://home.austin.rr.com/perks/basicx/Projects/
>
> Mike, what produced those beautiful virtual board images?
>
You mean like this -
http://home.austin.rr.com/perks/basicx/Projects/PWM%20Controller.JPG ?

I would like to say that its all my own work but it isn't. There is a
ULP (user language program) for Eagle called Eagle3D written by Matthias
Weißer (http://www.matwei.de/eng/index.php?page1=eagle3d ). This program
(with a bit of coaxing) creates a 3D drawing from a Eagle BRD file. Then
you use a program called POVRay (http://www.povray.org/ ) to render that
3D drawing. I use Eagle to help do the board layout even for stripboard
as it reduce errors.

I haven't finished writing up the PWM Controller project but here is a
side by side comparison with the completed circuit:
http://home.austin.rr.com/perks/basicx/Projects/PWM%20Controller2.JPG .
You almost can't tell the difference ;)

It sounds like I also need to write up something on my prototyping
methodology - it seems to work quite nicely for me and stripboard helps
with eliminating a lot of the rats nest associated with prototyping on
just perfboard. However I still haven't found a good tool to help with
design errors or inadvertent solder bridges ;)

Regards,
Mike





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Cool Mike, I used Povray many years ago for 3d rendering. I can
tell you put a lot of thought into the result. Now to just get it to
not overlay circuits ;)

thanks,
Don Lewis --- In basicx@basi..., Mike Perks <basicx@a...> wrote:
> Tom Becker wrote:
>
> > > http://home.austin.rr.com/perks/basicx/Projects/
> >
> > Mike, what produced those beautiful virtual board images?
> >
> You mean like this -
> http://home.austin.rr.com/perks/basicx/Projects/PWM%20Controller.JPG ?
>
> I would like to say that its all my own work but it isn't. There is a
> ULP (user language program) for Eagle called Eagle3D written by
Matthias
> Weißer (http://www.matwei.de/eng/index.php?page1=eagle3d ). This
program
> (with a bit of coaxing) creates a 3D drawing from a Eagle BRD file.
Then
> you use a program called POVRay (http://www.povray.org/ ) to render
that
> 3D drawing. I use Eagle to help do the board layout even for stripboard
> as it reduce errors.
>
> I haven't finished writing up the PWM Controller project but here is a
> side by side comparison with the completed circuit:
> http://home.austin.rr.com/perks/basicx/Projects/PWM%20Controller2.JPG .
> You almost can't tell the difference ;)
>
> It sounds like I also need to write up something on my prototyping
> methodology - it seems to work quite nicely for me and stripboard helps
> with eliminating a lot of the rats nest associated with prototyping on
> just perfboard. However I still haven't found a good tool to help with
> design errors or inadvertent solder bridges ;)
>
> Regards,
> Mike




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