Question PWM and circut in stamp app notes 1
I've got an application where I need to drive 20 LED's wired in
serial off of one pin wich using pwm to output a voltage between 0
and 5V. The software is doing alot of other stuff, so I won't be able
to issue the PWM command very often to update the voltage on the pin.
I'm thinking of using a circut like is described in the basic stamp
application notes 1
http://www.google.ca/search?
q=cache:2G7CE655Hc8C:www.pond.ie/ftp/stamp1_apps/pwm.pdf+pwm+basic+sta
mp&hl=en (HTML version, no graphics)
http://www.pond.ie/ftp/stamp1_apps/pwm.pdf (PDF version with graphics)
It's the one using the ca5160 op amp to keep a constant voltage, and
I would hook the output up to some kind of transistor that could
handle the larger current load.
Problem is, that op-amp is hard to find, especially here in Canada.
Can anyone suggest a similar circut, made of easily found parts?
(i've searched the archives here & couldn't find anything)
Again, the goal is to be able to set the voltage on the circut using
one pwm command, and be able to 'forget' about it for a while
(probably up to .5 or 1 sec) but have the output stay at the voltage
it was set to.
Any help would be greatly appreciated.
serial off of one pin wich using pwm to output a voltage between 0
and 5V. The software is doing alot of other stuff, so I won't be able
to issue the PWM command very often to update the voltage on the pin.
I'm thinking of using a circut like is described in the basic stamp
application notes 1
http://www.google.ca/search?
q=cache:2G7CE655Hc8C:www.pond.ie/ftp/stamp1_apps/pwm.pdf+pwm+basic+sta
mp&hl=en (HTML version, no graphics)
http://www.pond.ie/ftp/stamp1_apps/pwm.pdf (PDF version with graphics)
It's the one using the ca5160 op amp to keep a constant voltage, and
I would hook the output up to some kind of transistor that could
handle the larger current load.
Problem is, that op-amp is hard to find, especially here in Canada.
Can anyone suggest a similar circut, made of easily found parts?
(i've searched the archives here & couldn't find anything)
Again, the goal is to be able to set the voltage on the circut using
one pwm command, and be able to 'forget' about it for a while
(probably up to .5 or 1 sec) but have the output stay at the voltage
it was set to.
Any help would be greatly appreciated.
Comments
>serial off of one pin wich using pwm to output a voltage between 0
>and 5V. The software is doing alot of other stuff, so I won't be able
>to issue the PWM command very often to update the voltage on the pin.
>...
Hi, Here's a circuit that uses a common single supply op amp to
buffer the PWM signal. A transistor is hooked up as an emitter
follower in the feedback loop to supply the necessary led drive
current. The PWM has to get up above the 1.5 volt threshold before
the LEDs will start to light up.
+6 to +9v
|
o
;
BS2 100k 3|\|8 |
p0 --/\/\--o
|+\ 1 |/
|+ | >
| 2n2222
0.1uf === ;--|-/|4 |\e
| | 2|/ | |
| | | | 510 led
| `
/\/\---o---/\/\-->|--;
| | 10k |----/\/\-->|--|
| | | x20 |
| | `---/\/\-->|--|
| | |
o
o
o--Vss
op-amp=1/2 LM358
or other single-supply amp
good for ~5ma per led x 20
use a TO220 transistor for higher current
-- best regards
Tracy Allen
electronically monitored ecosystems
http://www.emesystems.com
mailto:tracy@e...
Why not use a Sample and Hold circuit?
You'd need two wires. "Sample", and "PWM in".
Using a low leakage capacitor, and a CA3140 OpAmp, you would not lose the
voltage for a VERY long time (I'm talking minutes here).
An example circuit to use, would be the Sample and Hold circuit I use in my
NiCad battery charger. Just remove the 555 timer, and control the 4066
switch from the stamp. Add current driving circuitry to the output of the S
and H cct to drive your load.
Using S and H, you can then let the Stamp do other things, and not worry
about refreshing the output voltage.
Ben, Wellington, NZ.
--
http://www.lennard.net.nz/
Ben Lennard, NCEE, Dip EE
Web Hosting and Electronics R&D
Club Coordinator, Victoria University of Wellington Hockey Club
Hm: +64 4 972 7567
Mb: +64 21 536 627
87 Spencer Street
Crofton Downs
Wellington
New Zealand
"To the optimist, the glass is half full. To the pessimist, the glass is
half empty. To the engineer, the glass is twice as big as it needs to be."
No animals were harmed in the transmission of this email, although the
Dog next door is living on borrowed time, let me tell you! Those of you
with an overwhelming fear of the unknown will be gratified to learn that
there is no hidden message revealed by reading this warning backwards.
>From: "dholowiski" <dholowiski@y...>
>To: basicstamps@yahoogroups.com
>Subject: [noparse][[/noparse]basicstamps] Question PWM and circut in stamp app notes 1
>Date: Sat, 6 Apr 2002 11:08 AM
>
> I've got an application where I need to drive 20 LED's wired in
> serial off of one pin wich using pwm to output a voltage between 0
> and 5V. The software is doing alot of other stuff, so I won't be able
> to issue the PWM command very often to update the voltage on the pin.
> I'm thinking of using a circut like is described in the basic stamp
> application notes 1
> http://www.google.ca/search?
> q=cache:2G7CE655Hc8C:www.pond.ie/ftp/stamp1_apps/pwm.pdf+pwm+basic+sta
> mp&hl=en (HTML version, no graphics)
> http://www.pond.ie/ftp/stamp1_apps/pwm.pdf (PDF version with graphics)
> It's the one using the ca5160 op amp to keep a constant voltage, and
> I would hook the output up to some kind of transistor that could
> handle the larger current load.
>
> Problem is, that op-amp is hard to find, especially here in Canada.
> Can anyone suggest a similar circut, made of easily found parts?
> (i've searched the archives here & couldn't find anything)
> Again, the goal is to be able to set the voltage on the circut using
> one pwm command, and be able to 'forget' about it for a while
> (probably up to .5 or 1 sec) but have the output stay at the voltage
> it was set to.
> Any help would be greatly appreciated.
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and
> Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>
but your circut looks a little complicated, I have to do this part 3X
over)
I was about to reply and say I can't understand the schematic you
typed out, but it turns out it just got messed up on my screen. When
I hit the reply button it changed the formatting & makes perfect
sense now.
I'm probably (hopefully) going to build it tomorrow, i'll let you
know how it works out.
Again, thanks very much.
--- In basicstamps@y..., Tracy Allen <tracy@e...> wrote:
> >I've got an application where I need to drive 20 LED's wired in
> >serial off of one pin wich using pwm to output a voltage between 0
> >and 5V. The software is doing alot of other stuff, so I won't be
able
> >to issue the PWM command very often to update the voltage on the
pin.
> >...
>
>
> Hi, Here's a circuit that uses a common single supply op amp to
> buffer the PWM signal. A transistor is hooked up as an emitter
> follower in the feedback loop to supply the necessary led drive
> current. The PWM has to get up above the 1.5 volt threshold before
> the LEDs will start to light up.
>
>
> +6 to +9v
> |
> o
;
> BS2 100k 3|\|8 |
> p0 --/\/\--o
|+\ 1 |/
> |+ | >
| 2n2222
> 0.1uf === ;--|-/|4 |\e
> | | 2|/ | |
> | | | | 510 led
> | `
/\/\---o---/\/\-->|--;
> | | 10k |----/\/\-->|--|
> | | | x20 |
> | | `---/\/\-->|--|
> | | |
>
o
o
o--Vss
>
>
> op-amp=1/2 LM358
> or other single-supply amp
> good for ~5ma per led x 20
> use a TO220 transistor for higher current
>
> -- best regards
> Tracy Allen
> electronically monitored ecosystems
> http://www.emesystems.com
> mailto:tracy@e...
just take the 2n2222 and replace it directly with the TO220 (of
course making sure pins/polarity is right) without making any changes
to the circut, right? My orange LED's need 20ma each X 20 LED's.
--- In basicstamps@y..., Tracy Allen <tracy@e...> wrote:
> >I've got an application where I need to drive 20 LED's wired in
> >serial off of one pin wich using pwm to output a voltage between 0
> >and 5V. The software is doing alot of other stuff, so I won't be
able
> >to issue the PWM command very often to update the voltage on the
pin.
> >...
>
>
> Hi, Here's a circuit that uses a common single supply op amp to
> buffer the PWM signal. A transistor is hooked up as an emitter
> follower in the feedback loop to supply the necessary led drive
> current. The PWM has to get up above the 1.5 volt threshold before
> the LEDs will start to light up.
>
>
> +6 to +9v
> |
> o
;
> BS2 100k 3|\|8 |
> p0 --/\/\--o
|+\ 1 |/
> |+ | >
| 2n2222
> 0.1uf === ;--|-/|4 |\e
> | | 2|/ | |
> | | | | 510 led
> | `
/\/\---o---/\/\-->|--;
> | | 10k |----/\/\-->|--|
> | | | x20 |
> | | `---/\/\-->|--|
> | | |
>
o
o
o--Vss
>
>
> op-amp=1/2 LM358
> or other single-supply amp
> good for ~5ma per led x 20
> use a TO220 transistor for higher current
>
> -- best regards
> Tracy Allen
> electronically monitored ecosystems
> http://www.emesystems.com
> mailto:tracy@e...
from the Stamp. They all run all the time. User SEROUT to control them.
http://www.al-williams.com/awce/pak5.htm
Al Williams
AWC
* Floating point math for the Stamp, PIC, SX, or any microcontroller
http://www.al-williams.com/awce/pak1.htm
>
Original Message
> From: dholowiski [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=3ZeyOD4J6IWQEsOxxapHJsJUL2IFrfrYBuXo0N3fiIdluSwtkqsrxNXK-NnP-ZttEBtJScQ-bGFiGmtxAA]dholowiski@y...[/url
> Sent: Friday, April 05, 2002 7:20 PM
> To: basicstamps@yahoogroups.com
> Subject: [noparse][[/noparse]basicstamps] Re: Question PWM and circut in stamp
> app notes 1
>
>
> Thanks, this sounds like exactly what i want. (Thanks as well Ben,
> but your circut looks a little complicated, I have to do this part 3X
> over)
> I was about to reply and say I can't understand the schematic you
> typed out, but it turns out it just got messed up on my screen. When
> I hit the reply button it changed the formatting & makes perfect
> sense now.
> I'm probably (hopefully) going to build it tomorrow, i'll let you
> know how it works out.
> Again, thanks very much.
> --- In basicstamps@y..., Tracy Allen <tracy@e...> wrote:
> > >I've got an application where I need to drive 20 LED's wired in
> > >serial off of one pin wich using pwm to output a voltage between 0
> > >and 5V. The software is doing alot of other stuff, so I won't be
> able
> > >to issue the PWM command very often to update the voltage on the
> pin.
> > >...
> >
> >
> > Hi, Here's a circuit that uses a common single supply op amp to
> > buffer the PWM signal. A transistor is hooked up as an emitter
> > follower in the feedback loop to supply the necessary led drive
> > current. The PWM has to get up above the 1.5 volt threshold before
> > the LEDs will start to light up.
> >
> >
> > +6 to +9v
> > |
> > o
;
> > BS2 100k 3|\|8 |
> > p0 --/\/\--o
|+\ 1 |/
> > |+ | >
| 2n2222
> > 0.1uf === ;--|-/|4 |\e
> > | | 2|/ | |
> > | | | | 510 led
> > | `
/\/\---o---/\/\-->|--;
> > | | 10k |----/\/\-->|--|
> > | | | x20 |
> > | | `---/\/\-->|--|
> > | | |
> >
o
o
o--Vss
> >
> >
> > op-amp=1/2 LM358
> > or other single-supply amp
> > good for ~5ma per led x 20
> > use a TO220 transistor for higher current
> >
> > -- best regards
> > Tracy Allen
> > electronically monitored ecosystems
> > http://www.emesystems.com
> > mailto:tracy@e...
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the
> Subject and Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to
http://docs.yahoo.com/info/terms/
>just take the 2n2222 and replace it directly with the TO220 (of
>course making sure pins/polarity is right) without making any changes
>to the circut, right? My orange LED's need 20ma each X 20 LED's.
That's 400 ma of total current. Zetex makes superb high gain, high
transistors (e.g. ZTX1051, from digikey), and even one of their TO92
superbeta transistors would run circles around the 2n2222. If you
use a TO220, find one with high (>100) gain, or even an NPN
darlington transistor. You can also use an N-channel mosfet as a
source follower in that same circuit, but it should be one with a Vgs
threshold of 3 volts or less. Feel free to ask if you have further
questions about the options, or about a specific part you have at
hand.
-- Tracy
>
>--- In basicstamps@y..., Tracy Allen <tracy@e...> wrote:
> > >I've got an application where I need to drive 20 LED's wired in
> > >serial off of one pin wich using pwm to output a voltage between 0
> > >and 5V. The software is doing alot of other stuff, so I won't be
>able
> > >to issue the PWM command very often to update the voltage on the
>pin.
> > >...
> >
> >
> > Hi, Here's a circuit that uses a common single supply op amp to
> > buffer the PWM signal. A transistor is hooked up as an emitter
> > follower in the feedback loop to supply the necessary led drive
> > current. The PWM has to get up above the 1.5 volt threshold before
> > the LEDs will start to light up.
> >
> >
> > +6 to +9v
> > |
> > o
;
> > BS2 100k 3|\|8 |
> > p0 --/\/\--o
|+\ 1 |/
> > |+ | >
| 2n2222
> > 0.1uf === ;--|-/|4 |\e
> > | | 2|/ | |
> > | | | | 510 led
> > | `
/\/\---o---/\/\-->|--;
> > | | 10k |----/\/\-->|--|
> > | | | x20 |
> > | | `---/\/\-->|--|
> > | | |
> >
o
o
o--Vss
> >
> >
> > op-amp=1/2 LM358
> > or other single-supply amp
> > good for ~5ma per led x 20
> > use a TO220 transistor for higher current
> >
> > -- best regards
> > Tracy Allen
> > electronically monitored ecosystems
> > http://www.emesystems.com
> > mailto:tracy@e...
>
>
>To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
>from the same email address that you subscribed. Text in the
>Subject and Body of the message will be ignored.
>
>
>Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/