Variable analog voltage from a digital circuit?

[mstacho]

In my old lab we had a board that was able to generate a variable (+/- 10 V) analog signal, but it appeared to be a digital board.  It worked by sending it the voltage you want from the PC, which had 12 bit precision, and then it would output the voltage.

Does anyone know how they did that?  Was it just PWM across an RC circuit or something?  I guess the crux of this question is: how does a Digital-to-Analog converter work?

MIKE

[waltr]

DAC (Digital to Analog Converter), google it.

[growler]

The only DAC I've built out of mostly discretes was an R-2R ladder, simple circuit once you get the concept but it needs a lot of separate inputs, one for each bit of precision. Also takes a lot of resistors of the same value.

[Daanii]

As far as I've seen, most DAC chips are resistor ladders or resistor strings. Again as far as I've seen, resistor strings are better but need more components than resistor ladders.

At one time I thought some DACs might be, as you say, pulse-width modulation with a resistor-capacitor filter. But apparently that does not work well.

[vinniewryan]

It can work well in unison with a variable voltage regulator. I've built DAC's this way, but your current is then limited to the chosen regulator.