8 input digital POT

Why don't you settle with 7 volume chips, use the 8th line for UP/DOWN select, and then just pulse the data lines to get the volume you want.

Chris

"exxos" wrote in news:42dea225$0$6475$ snipped-for-privacy@news-text.dial.pipex.com:

Sorry, I should have been a little more specific. It is for a motor speed control. I was hoping to use just a combination of high/low binary outputs to control the motor with 256 different settings. Thanks for the quick response though.

Colin wrote this in :

I'm sure there is a chip that does this. Otherwise, you can use a Digital to analog converter, and apply it as base current to a transistor... Depending on you application, that might be the best/easiest solution.

John Fields wrote in news: snipped-for-privacy@4ax.com:

Yes. A rheostat seems to be the thing I am looking for. But I need one that is controllable with 8 signals. Low signal is 0v and high is 5v

ah right, I ws thinking audio, but why not do that anyway ? instead of outputting a binary number, just pulse D0 either up or down 256 times, and use D1 to set speed up or speed down... since your output is a PC controled code, just alter the program to output pulses instead. A fraction more complex program, but a lot easier than trying to find IC pots to fit the job.

Chris

Analog Devices (as well as others) make a few nice packages that are serial controlled (I2C). That way you can call a setpoint serialy directly to the chip, without the step - up, step - down increments. If you need parallel, of course, you only need to add a serial to parallel converter.

I designed with the AD5232 (1024 position) and the folks at AD were very helpful by forwarding examples of VB code.

Colin wrote this in :

Depending on your circuit, a DA-converter and a transistor should do this. Simply feed a fet-transistor or bipolar one (depending on the motor) from the DA. The DAC can have 8 bits in, which will give 255 discrete levels.

Think R-2R ladder. This will be most suitable for your 8 bit parallel port requirement. Google for it. There are many devices with varying levels of on chip interface logic. I am sure you can find something that fits the bill.

Jeff

"Jeff Thon" wrote in news:1YADe.1390$ snipped-for-privacy@newssvr21.news.prodigy.com:

Ah, this R-2R thing looks like exactly what I'm after. One thing I am having a hard time understanding is why there is an op-amp after all of the resistors in the circuits I am finding. So I guess my questions would be, what is this op-ampo for, and is this a special type of op-amp, I can't find one anywhere that looks like that, with 3 connections, all the ones I see have 5, and I don't know what the other 2 are for. Thanks for getting me on the right track. Colin