# Digital Potentiometers - implementation ?'s

Discussion in 'Electronic Design' started by Jason Stoddard, Nov 15, 2003.

1. ### Jason StoddardGuest

I wonder if somebody can add a couple wrinkles to my grey matter. I am a
bit new to these. I am looking at a digital potentiometer:

(DS1866 - http://rocky.digikey.com/WebLib/Dallas/Dallas Web%
20Data/DS1866.pdf)

I am putting together a micro controlled circuit for a school project. I
would like to have a micro output signals to drive the digital
potentiometer and use it as a dimmer for some LED's or other low voltage
light.

My question is on how to read the data sheet to determine how much
current I can run through the resistor network? Can I run my LED's
directly through these resistors? or do I need to use these resistors to
drive another circuit?

Thanks!

Jason

2. ### Frank BemelmanGuest

I have not looked up the datasheet, but often these chips come
with different resistor values, the smallest being 10K. That is
a bit too high resistance for direct control of a led.

You could use it to control a voltage, from 0V-5V, and use
and opamp follower to give you a bit more current for your
led(s).

3. ### Luhan MonatGuest

Jason,

Digital potentiomenters have their uses - dimming lights is not one of
them. You can do it, but why not just drive a simple transistor with
the micro's output. Vary the duty cycle of a series of pulses in
software (PWM) and control a lot of power with very little loss.

4. ### BanGuest

Frank Bemelman wrote:
|||
||| I am putting together a micro controlled circuit for a school
||| project. I would like to have a micro output signals to drive the
||| digital potentiometer and use it as a dimmer for some LED's or
||| other low voltage light.
|||
||| My question is on how to read the data sheet to determine how much
||| current I can run through the resistor network? Can I run my LED's
||| directly through these resistors? or do I need to use these
||| resistors to drive another circuit?
||
|| I have not looked up the datasheet, but often these chips come
|| with different resistor values, the smallest being 10K. That is
|| a bit too high resistance for direct control of a led.
||
|| You could use it to control a voltage, from 0V-5V, and use
|| and opamp follower to give you a bit more current for your
|| led(s).
||
||
|| --
|| Thanks, Frank.

It will much better to create the dimming by software inside the PIC with
PWM.
To the LED I would use this kind of interface, a current source:
It needs only 1V, the rest is available for the LEDs, it is also short
circuit proof.

+5...20V
o--|<--|<--o
2N3906 | LED LED
port ___ |/
o--|___|--+--|
4k7 | |>
V |
1N4148 - |
| .-.
| | |
V | |R= 0.66V/20mA = 33 ohms
1N4148 - '-'
| |
| |
=== ===
GND GND
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

ciao Ban

5. ### Frank BemelmanGuest

Yes, 100% agreed. But the question seems to focus on using a digital
pot, for educational purposes.