Arduino as a variable resistor/rheostat?


I'm attempting to use an Arduino to control a video camera's iris and focus remotely. The camera has 3.5mm connector with four pins: a reference voltage, iris, focus, and auto/manual focus select. The auto/manual pin is simple: open is manual, closed is auto. The focus and iris, however, each require a 20k rheostat.

My question is: how can I use an Arduino in place of the rheostats? I.e., given an analog input, how can I apply a variable amount of resistance to it and send it back? Is it possible with PWM? Is there such a thing as a digital rheostat?

I looked at using a digital pot, like the one in the SPIDigitalPot tutorial (from the Arduino tutorials page), but I'm unsure how to wire it. I could use the reference from the camera for VDD, but what would I use for VSS? And wouldn't VDD need to be logic level from the Arduino for the digipot to understand the SPI input?

Sorry if any of my terminology is incorrect. I'm new to electronics, and I appreciate any help or pointers I can get!


Without knowing anything about the internal wiring inside the camera, digital potentiometers are the defensive approach.
There is no tight electrical connection between the pot and the controlling Arduino, similar as with optocouples.

Just connect the pins H, L, and W (at least this is what they are labelled generally) to the camera inputs .

Thanks for the quick reply. It’s good to know a digital pot will help me not damage a really expensive camera!

At least I know I’m looking in the right direction with the digital pot. Considering what you wrote, one thing I didn’t understand was what I should connect the low pin to, since I’m only getting the “high” value from the camera. Do I just tie it to the W output?

+5V --> VDD |          |
GND --> VSS |          | A1 <----- Reference In -->
D11 --> SDI |  AD5206  | W1 <--+-- Iris Out ------>
D10 --> CS  |          |       |
D13 --> CLK |          | B1 <--+

By the way, this is the tutorial I’m referring to:

Ooops, a SIX channel pot - are you sure it costs really less than the camera? :wink:
So the camera does not need a rheostat, but just a resistor. Simply connect Wx and Bx, You could leave Bx open, but it is good practice to tie it to Wx.

You see, the part “between W and B” is shortcut by this, so to speak.

Thanks for all your help! I think I know what I need to do now. I just have to buy the parts and wire it up!

The only other thing I'm not quite sure about is the resistance. Most of the pots I've found are 10k, 50k, or 100k, but the camera apparently wants 0–20k. I may just try it with 10 and see how it works. I don't think 50k would give me enough resolution unless I can find a 10-bit pot.