[sdiy] Help, I'm Desperate! (Charge Injection with DG408)

David G Dixon dixon at mail.ubc.ca
Wed Dec 5 19:33:15 CET 2018

> Lm3914 is in last time buy status, although thousands 
> available for sale.
> Is there a block diagram of this circuit?  I'd like to better 
> understand what you want this module to do.

OK, I've figured out what I'm going to try next.  Forget LM3914.  I'm simply
going to use two LM339 quad comparators.  I'm going to convert my -5V to +5V
CV to a 0 to 5V CV (one opamp), then create a seven-comparator flash cascade
driven between 0 and 5V to generate the input to a CD4532 8-to-3 bit
priority encoder.  All logic levels will be between 0 and 5V, so there will
be no problems with CMOS input level incompatibility.  The CD4532 will drive
the DG408 chips.

I'm thinking that this will work well because the comparator cascade will
give me very clean signals that will only change one-at-a-time, so at most
the 4532 will only ever toggle between two states.  The delay between
successive output bits of the 4532 firing should be well within the time it
takes for the DG408 to switch, so not using Gray code should not be an

If this doesn't provide suitable logic inputs to those multiplexers, then
I'm going to set my workbench on fire and take up basket weaving.

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