[sdiy] CMOS 4516+4067 questions

[jh.]

> chip. THe way I'd figured out to do the CV channels was to have a 4067 for
> each set of 16 and to run a 51K resistor from +15 V to the common pin,
then
> have each demuxed output go to a 100K pot, thus getting 10V across the
pot.
> These would then all feed 100K resistors into an inverting summer, which
> would then feed to the main I/O board where another inverting buffer would
> turn it the right way round and send it to the oputside world......
>
> First question...is this a right/sensible way to do it.....

Take the loading from summing resitors into account, and, more important,
tolerances for pots are normally much worse than for resistors, and then
there is the different temperature response. My advice: Use an opamp for a
buffered +10V source, with a resistor (few kiloOhms) at the opamp output,
but inside the feedback loop, so you get precision without much extra
effort.

JH.