[sdiy] CMOS 4516+4067 questions

[Grant Richter]

> 
> First question...is this a right/sensible way to do it.....this sequencer
> could end up with 12 or more banks of 16 steps when finished (I want to use
> it onstage), I didn't want to have 200 odd pots permanently powered, this
> way only one pot per bank at a time is drawing current ( I know it isn't a
> lot but 200 of them would be more significant), also the fact that ther are
> resistors both sides of the 4067 should provide some protection in fault
> conditions......

Have you considered using a voltage multiplexer? It is a bit odd to use a
logic chip and then "hotwire" it for analog, when you have dedicated analog
chips like the CD4051 multiplexer. For instance generate a 10 volt supply
with an op-amp. Then use two CD4051s to demultiplex (4051s are
bidirectional) it to the top of each pot. You have already saved 16 51K
resistors and have a more precise method. Plus you can adjust the range of
the entire sequence by varying the reference (10 volt) voltage.

A CD4051 will handle enough current to power LEDs from the same supply. So
you can wire LEDs across the pots with 2.2K resistors. A TL074 will supply
10ma or better, enough to drive LEDs.


> Number 3: What sort of fan-out will I get out of a 4516?...I think I need
> five plus the buffers below on the main panel, will I get that OK?

4000 series CMOS outputs about 10 ma, gate input current is 1 ua so fanout
is like 1000 gates. Don't worry at low speeds.

> Number 4: If I use a TL074 to buffer the outputs will I be able to send the
> four-digit output of the 4516 out to another board?

Use B series CMOS, it's buffered already. Plenty of output drive.