Digital Potentiometers (Encoders)

**Gutter** · 03-25-2004, 08:05 PM

Anybody have experience with these? I'm working on a project that involves interfacing a potentiometer to a PC. For simplicity's sake, lets just say that when the user turns the potentiometer, a number changes on the user's screen representing the voltage changes.

From the research I've done, it looks like I'd have to use a data aquisition board (expensive) in order to do this with an analog potentiometer. I found these "digital" potentiometers in a mouser catalog which claim to output a square wave automagically (implying that an A/D conversion is not necessary).

Do any of you know what's involved in using these for the purpose I described? I have 4-5 potentiometers that will need to be polled.

**Arby** · 03-26-2004, 01:25 PM

How are you interfacing it? Parallel or serial? If it's parallel, you could probably find a cheap, 8 bit A/D converter and hook that up to an analog pot.

The potentiometers you mention probably aren't potentiometers at all, but, um, dial thingies. They won't give you a value between min and max, but will only tell you when it goes up or down. Turn it left and it sends one signal, the other way a different signal. They work like the volume knobs on most modern stereos. This may work for you, though.

**Arby** · 03-26-2004, 01:30 PM

The only "digital potentiometers" I can find on mouser are the other way... you give them a digital value and they change their resistance. Can you post a link to the one you found or give me the part number?

**god_of_cpu** · 03-26-2004, 02:31 PM

Check out these Data Acquisition Modules. I'm not sure, but they might be able to do what you want.

You could also use the analog to digital converter on your game port. I did this to get my steering wheel controls to work. They sent out 1.5v,3v,or 5v of current based on what button was pressed and I connected that directly to a joystick axis line.

**Gutter** · 03-26-2004, 03:04 PM

Arby, that's basically all I need.

I doubt it'd be that easy, so I'm probably going to procure this:
http://www.al-williams.com/gp3.htm

Unfortunately it requires 9V, so I can't just power it off of the USB port.

The Mouser catalog doesn't have any technical details, but this site is what explained how it works:
Long URL, click here

Actually, the Rotary Encoder on page 380 of the latest mouser catalog has a tiny bit of detail.

This will be implemented on an Epia V8000A, so no gameport available. Either serial or parallel port.

**Arby** · 03-26-2004, 06:32 PM

That link you have for the digital pots doesn't seem to be what you want. They take a digital signal from the computer and generate an analog resistance. It doesn't seem like they work the other way around.

The easiest thing you could do would be a pic. Something like the Microchip 16F877 - I've used this chip before. It has 8, 0-5V analog>digital inputs, and has serial communications built into the chip. They cost a whopping $7-8

I have a programmer, they're cheap, you can get them for less than $20. I could send you code that I've already done, and help you modify it if need be.

I had a project that never got off the ground because I can't figure out how to get my program to access the parallel or serial port in 2000/XP

Maybe we can help each other.

**Cherub211** · 03-26-2004, 06:44 PM

I did this by programming a PIC micro to convert an analog signal to a digital value and output the digital value via RS-232 (serial) to a computer.

**Arby** · 03-26-2004, 06:54 PM

Originally Posted by Cherub211

I did this by programming a PIC micro to convert an analog signal to a digital value and output the digital value via RS-232 (serial) to a computer.

That's a good summary of my post above yours.

**Cherub211** · 03-26-2004, 06:56 PM

HAHA, I didn't read it sorry. I used a 16F877 too, I work at Microchip though, so I got paid to do it.

I however did get the port to work on XP. Use hyperterminal.

**Curiosity** · 03-26-2004, 10:15 PM

If it really outputs resistance like a potentiometer, just use a USB gamepad. The Logitech RumblePad that I'm using has 5 A/D converters on it, and like 12+ buttons, and couple A/Ds for output. The drawback is that it auto-centers when it's powered up, so it's readings are relative, or in other words, whatever the resistance is when it starts is the center.