[Coco] It's a small win, but a win nonetheless

[RETRO Innovations]

On 3/11/2017 4:18 PM, Gene Heskett wrote:
> Do not forget that if the input r on the comparator's input is 10 megs,
> your taking a look at it withe a 10x scope probe, or a dvm lead, either
> the scope or the dvm is another 10 meg r, so the resting voltage you
> measure is really twice that.
I agree with your premise, but it must not be twice, because when I 
remove the probe, it still works fine.  The 10M resistor to ground is 
still installed, though.
>
> If that 1uf is a small electrolytic, its leakage could account for that.
It could, I will see if I can find a 1uF in another type to try.
> Also the comparators input current has to flow thru that r so you might
> want to switch comparator types from one with a starved current pnp
> input stage, to one with depletion mode fet inputs, which have femtoamps
> for input currents. Neither of us has gear to measure that low a
> currant.
True, but I am going for ultra low parts count, and if I can use the 
comparator of the uC, it'll save an IC and a few passives.  The design 
is price sensitive.
> Which input is getting the hysteresis feedback?
+
> Needs 2 stop bits? More positive framing sync, but will the music
> tolerate that?  I dunno.
Well, it would be nice, but the Coco does not provide any stop bits :-)  
And, I can't add any.

Jim