[sdiy] Static ADC and DAC recommendations?

[MTG]

It takes a fair bit of current to activate a zener diode, and I think it 
would be difficult to achieve that going into the base of a transistor.

GB

On 1/26/2013 11:00 PM, Paul Anderson wrote:
> Alright here's my wacky idea for a circuit:
>
> Signal goes to an op-amp, then into a series of parallel Zener diodes connected to the base of several transistors. The values of the zeners have to be chosen to conduct at sensible voltages for each of the possible output values. The transistors then feed into an appropriate logic gate setup to make sure that the right values appear.
>
> It should work, but bear in mind *it will work very badly*.  No clock means that the output values will change while they are being read, which can lead to weirdness. Further, the number of diodes and transistors required goes up exponentially with the number of bits, so it's only feasible to build a very low bit converter. Eight bits of resolution means you'd need 256 diodes and transistors driving the logic gates.
>