18f4685 6 seg clock - dim display

Started by sr_gamer May 1, 2009
if you look in the files section under sr_gamer you will find the schematic and the program for a clock I'm building. The display is VERY dim.

I'd like the display to be very bright.

These elements are very bright when supplied with 5v, which should be what is coming off of the PIC, so I'm either suffering from low duty cycle or having trouble sourcing enough current. I tried some 1k pull up resistors between the pins labeled anodes and +5v, but this didn't seem to affect the situation.

Hi,

Your diagram shows no current limiting resistors for each segment, is this correct or do you have some?
I had a play with 7 segments once, and had a similar problem, it was a long time ago...
I've heard of two versions of updating the segments, using the LSB of Timer0 to update each segment depending on the value (00 = Segment 1, 01 Segment 2 etc), or every time Timer0 rolls over, change segment.
I tried using timers but found the last segment was always the brightest, as all the calculations were happening while it was on, giving a longer on time..

Hope to of helped,
Paul
From: sr_gamer
Sent: Monday, April 13, 2009 9:31 PM
To: p...
Subject: [piclist] 18f4685 6 seg clock - dim display

if you look in the files section under sr_gamer you will find the schematic and the program for a clock I'm building. The display is VERY dim.

I'd like the display to be very bright.

These elements are very bright when supplied with 5v, which should be what is coming off of the PIC, so I'm either suffering from low duty cycle or having trouble sourcing enough current. I tried some 1k pull up resistors between the pins labeled anodes and +5v, but this didn't seem to affect the situation.
Don't source the current, SINK it. Sometimes an IC can sink more then it
can source.

Alan KM6VV

>
> if you look in the files section under sr_gamer you will find the
> schematic and the program for a clock I'm building. The display is VERY
> dim.
>
> I'd like the display to be very bright.
>
> These elements are very bright when supplied with 5v, which should be what
> is coming off of the PIC, so I'm either suffering from low duty cycle or
> having trouble sourcing enough current. I tried some 1k pull up resistors
> between the pins labeled anodes and +5v, but this didn't seem to affect
> the situation.

Oh, just noticed, you'll prob be struggling to light up all 7 segments using one pic output, especially with no current limiting.
I would be tempted to use common cathode segments, with a nice NPN transistor on the pic output to sink the segments, and the pic to supply a "high" to turn on the segment

Paul
From: sr_gamer
Sent: Monday, April 13, 2009 9:31 PM
To: p...
Subject: [piclist] 18f4685 6 seg clock - dim display

if you look in the files section under sr_gamer you will find the schematic and the program for a clock I'm building. The display is VERY dim.

I'd like the display to be very bright.

These elements are very bright when supplied with 5v, which should be what is coming off of the PIC, so I'm either suffering from low duty cycle or having trouble sourcing enough current. I tried some 1k pull up resistors between the pins labeled anodes and +5v, but this didn't seem to affect the situation.
this is correct, no limiting resistors are needed. I can run this display at 100% duty cycle at 5V

--- On Fri, 5/1/09, Paul Laverick wrote:
From: Paul Laverick
Subject: Re: [piclist] 18f4685 6 seg clock - dim display
To: p...
Date: Friday, May 1, 2009, 5:23 PM

Hi,

Your diagram shows no current limiting resistors
for each segment, is this correct or do you have some?
I had a play with 7 segments once, and had a
similar problem, it was a long time ago...
I've heard of two versions of updating the
segments, using the LSB of Timer0 to update each segment depending on the value
(00 = Segment 1, 01 Segment 2 etc), or every time Timer0 rolls over, change
segment.
I tried using timers but found the last segment was
always the brightest, as all the calculations were happening while it was on,
giving a longer on time..

Hope to of helped,
Paul

From: sr_gamer
Sent: Monday, April 13, 2009 9:31 PM
To: piclist@yahoogroups .com
Subject: [piclist] 18f4685 6 seg clock - dim
display

if you look in the files section under sr_gamer you will find the schematic
and the program for a clock I'm building. The display is VERY dim.

I'd
like the display to be very bright.

These elements are very bright when
supplied with 5v, which should be what is coming off of the PIC, so I'm either
suffering from low duty cycle or having trouble sourcing enough current. I tried
some 1k pull up resistors between the pins labeled anodes and +5v, but this
didn't seem to affect the situation.
yeah.. I was hoping to not have to modify the board, but that looks like the way to go.

--- On Fri, 5/1/09, Alan Marconett wrote:
From: Alan Marconett
Subject: RE: [piclist] 18f4685 6 seg clock - dim display
To: p...
Date: Friday, May 1, 2009, 5:27 PM

Don't source the current, SINK it. Sometimes an IC can sink more then it

can source.

Alan KM6VV

>

> if you look in the files section under sr_gamer you will find the

> schematic and the program for a clock I'm building. The display is VERY

> dim.

>

> I'd like the display to be very bright.

>

> These elements are very bright when supplied with 5v, which should be what

> is coming off of the PIC, so I'm either suffering from low duty cycle or

> having trouble sourcing enough current. I tried some 1k pull up resistors

> between the pins labeled anodes and +5v, but this didn't seem to affect

> the situation.
This is another route that I considered. For the moment, I'm suffering with the dim display and working on various programs. Next time I get the iron out to make a display there will be some hefty revisions.

--- On Fri, 5/1/09, Paul Laverick wrote:
From: Paul Laverick
Subject: Re: [piclist] 18f4685 6 seg clock - dim display
To: p...
Date: Friday, May 1, 2009, 5:34 PM

Oh, just noticed, you'll prob be struggling to
light up all 7 segments using one pic output, especially with no current
limiting.
I would be tempted to use common cathode segments,
with a nice NPN transistor on the pic output to sink the segments, and the pic
to supply a "high" to turn on the segment

Paul

From: sr_gamer
Sent: Monday, April 13, 2009 9:31 PM
To: piclist@yahoogroups .com
Subject: [piclist] 18f4685 6 seg clock - dim
display

if you look in the files section under sr_gamer you will find the schematic
and the program for a clock I'm building. The display is VERY dim.

I'd
like the display to be very bright.

These elements are very bright when
supplied with 5v, which should be what is coming off of the PIC, so I'm either
suffering from low duty cycle or having trouble sourcing enough current. I tried
some 1k pull up resistors between the pins labeled anodes and +5v, but this
didn't seem to affect the situation.
No wonder your display is dim. You can't drive it like that.
Assuming this PIC is like the earlier 18series it'll have some limitations:
Max 20mA sink on any one pin, and max 20mA on all pins summed.
You have 6x8 = 48 segments, and for top brightness expect 20mA pr segment...
thats 960mA when all are lit (which should also be a design goal).
No way a PIC can deliver that without burning up, and certainly not without
excessive voltage drop on outputs.

You'll have to use both segment driver and display driver. Thats the only
way to get it 'very bright'. I'd suggest using MOS drivers for both
digit and segmens
as this way you can drop all those base resistors.

Here in this clock I've used bipolar drivers, good bright display but
with MOSFET
drives 22 resistors could have been removed (8 in the SIL).

HTH
Shadowrun Gamer skrev:
> this is correct, no limiting resistors are needed. I can run this
> display at 100% duty cycle at 5V
>
> --- On *Fri, 5/1/09, Paul Laverick //* wrote:
>
> From: Paul Laverick
> Subject: Re: [piclist] 18f4685 6 seg clock - dim display
> To: p...
> Date: Friday, May 1, 2009, 5:23 PM
>
> Hi,
>
> Your diagram shows no current limiting resistors for each segment,
> is this correct or do you have some?
> I had a play with 7 segments once, and had a similar problem, it
> was a long time ago...
> I've heard of two versions of updating the segments, using the LSB
> of Timer0 to update each segment depending on the value (00 > Segment 1, 01 Segment 2 etc), or every time Timer0 rolls over,
> change segment.
> I tried using timers but found the last segment was always the
> brightest, as all the calculations were happening while it was on,
> giving a longer on time..
>
> Hope to of helped,
> Paul
>
> *From:* sr_gamer
> *Sent:* Monday, April 13, 2009 9:31 PM
> *To:* piclist@yahoogroups .com
> *Subject:* [piclist] 18f4685 6 seg clock - dim display
>
> if you look in the files section under sr_gamer you will find the
> schematic and the program for a clock I'm building. The display is
> VERY dim.
>
> I'd like the display to be very bright.
>
> These elements are very bright when supplied with 5v, which should
> be what is coming off of the PIC, so I'm either suffering from low
> duty cycle or having trouble sourcing enough current. I tried some
> 1k pull up resistors between the pins labeled anodes and +5v, but
> this didn't seem to affect the situation.
>

--
*******************************************
VISIT MY HOME PAGE:

LAST UPDATED: 23/08/2003
*******************************************
Regards
Eirik Karlsen
There are the newer "digital" transistors out there that have the bias resistors 'built-in' to save board space, part count, and costs... The lowest cost ones are $0.015 each and come in a nice small but not too small SOT23 package. Here is one from On-Semi, MMUN2214LT1G.
--- In p..., Eirik Karlsen wrote:
>
> No wonder your display is dim. You can't drive it like that.
> Assuming this PIC is like the earlier 18series it'll have some limitations:
> Max 20mA sink on any one pin, and max 20mA on all pins summed.
> You have 6x8 = 48 segments, and for top brightness expect 20mA pr segment...
> thats 960mA when all are lit (which should also be a design goal).
> No way a PIC can deliver that without burning up, and certainly not without
> excessive voltage drop on outputs.
>
> You'll have to use both segment driver and display driver. Thats the only
> way to get it 'very bright'. I'd suggest using MOS drivers for both
> digit and segmens
> as this way you can drop all those base resistors.
>
> Here in this clock I've used bipolar drivers, good bright display but
> with MOSFET
> drives 22 resistors could have been removed (8 in the SIL).
>
> HTH
> Shadowrun Gamer skrev:
> >
> >
> > this is correct, no limiting resistors are needed. I can run this
> > display at 100% duty cycle at 5V
> >
> > --- On *Fri, 5/1/09, Paul Laverick //* wrote:
> >
> > From: Paul Laverick
> > Subject: Re: [piclist] 18f4685 6 seg clock - dim display
> > To: p...
> > Date: Friday, May 1, 2009, 5:23 PM
> >
> > Hi,
> >
> > Your diagram shows no current limiting resistors for each segment,
> > is this correct or do you have some?
> > I had a play with 7 segments once, and had a similar problem, it
> > was a long time ago...
> > I've heard of two versions of updating the segments, using the LSB
> > of Timer0 to update each segment depending on the value (00 > > Segment 1, 01 Segment 2 etc), or every time Timer0 rolls over,
> > change segment.
> > I tried using timers but found the last segment was always the
> > brightest, as all the calculations were happening while it was on,
> > giving a longer on time..
> >
> > Hope to of helped,
> > Paul
> >
> > *From:* sr_gamer
> > *Sent:* Monday, April 13, 2009 9:31 PM
> > *To:* piclist@yahoogroups .com
> > *Subject:* [piclist] 18f4685 6 seg clock - dim display
> >
> > if you look in the files section under sr_gamer you will find the
> > schematic and the program for a clock I'm building. The display is
> > VERY dim.
> >
> > I'd like the display to be very bright.
> >
> > These elements are very bright when supplied with 5v, which should
> > be what is coming off of the PIC, so I'm either suffering from low
> > duty cycle or having trouble sourcing enough current. I tried some
> > 1k pull up resistors between the pins labeled anodes and +5v, but
> > this didn't seem to affect the situation.
> >
> >
> > --
> *******************************************
> VISIT MY HOME PAGE:
>
> LAST UPDATED: 23/08/2003
> *******************************************
> Regards
> Eirik Karlsen
>

Yes I've seen these used extensively in some high value industrial
electronics (radars etc)...
Nice puppys but who has these laying around when yah need'em ?
demolitron skrev:
> There are the newer "digital" transistors out there that have the bias
> resistors 'built-in' to save board space, part count, and costs... The
> lowest cost ones are $0.015 each and come in a nice small but not too
> small SOT23 package. Here is one from On-Semi, MMUN2214LT1G.
>
> --- In p... ,
> Eirik Karlsen wrote:
> >
> > No wonder your display is dim. You can't drive it like that.
> > Assuming this PIC is like the earlier 18series it'll have some
> limitations:
> > Max 20mA sink on any one pin, and max 20mA on all pins summed.
> > You have 6x8 = 48 segments, and for top brightness expect 20mA pr
> segment...
> > thats 960mA when all are lit (which should also be a design goal).
> > No way a PIC can deliver that without burning up, and certainly not
> without
> > excessive voltage drop on outputs.
> >
> > You'll have to use both segment driver and display driver. Thats the
> only
> > way to get it 'very bright'. I'd suggest using MOS drivers for both
> > digit and segmens
> > as this way you can drop all those base resistors.
> >
> > Here in this clock I've used bipolar drivers, good bright display but
> > with MOSFET
> > drives 22 resistors could have been removed (8 in the SIL).
> >
> > >
> > HTH
> >
> >
> > Shadowrun Gamer skrev:
> > >
> > >
> > > this is correct, no limiting resistors are needed. I can run this
> > > display at 100% duty cycle at 5V
> > >
> > > --- On *Fri, 5/1/09, Paul Laverick //* wrote:
> > >
> > > From: Paul Laverick
> > > Subject: Re: [piclist] 18f4685 6 seg clock - dim display
> > > To: p...
> > > Date: Friday, May 1, 2009, 5:23 PM
> > >
> > > Hi,
> > >
> > > Your diagram shows no current limiting resistors for each segment,
> > > is this correct or do you have some?
> > > I had a play with 7 segments once, and had a similar problem, it
> > > was a long time ago...
> > > I've heard of two versions of updating the segments, using the LSB
> > > of Timer0 to update each segment depending on the value (00 > > > Segment 1, 01 Segment 2 etc), or every time Timer0 rolls over,
> > > change segment.
> > > I tried using timers but found the last segment was always the
> > > brightest, as all the calculations were happening while it was on,
> > > giving a longer on time..
> > >
> > > Hope to of helped,
> > > Paul
> > >
> > > *From:* sr_gamer
> > > *Sent:* Monday, April 13, 2009 9:31 PM
> > > *To:* piclist@yahoogroups .com > >
> > > *Subject:* [piclist] 18f4685 6 seg clock - dim display
> > >
> > > if you look in the files section under sr_gamer you will find the
> > > schematic and the program for a clock I'm building. The display is
> > > VERY dim.
> > >
> > > I'd like the display to be very bright.
> > >
> > > These elements are very bright when supplied with 5v, which should
> > > be what is coming off of the PIC, so I'm either suffering from low
> > > duty cycle or having trouble sourcing enough current. I tried some
> > > 1k pull up resistors between the pins labeled anodes and +5v, but
> > > this didn't seem to affect the situation.
> > >
> > >
> > >
> >
> > --
> > *******************************************
> > VISIT MY HOME PAGE:
> > > >
> > LAST UPDATED: 23/08/2003
> > *******************************************
> > Regards
> > Eirik Karlsen
> >

--
*******************************************
VISIT MY HOME PAGE:

LAST UPDATED: 23/08/2003
*******************************************
Regards
Eirik Karlsen