[sdiy] Adding reset clock to CD4520

[Roman Sowa]

First of all, tying 13 with 15 is pointless. It is there only to reset 
the counter after 4 clocks, making it modulo 4, but since you want only 
2 LSBs (pins 11-12) there's no difference if it counts to 4, 8 or 16. 
Might have more sense if it was 4518 and not 4520. So cut this 
connection. Like it is now, the inverter's reset pulse forces counter 
output (13) to high level, so if the inverter isn't strong enough, 
external reset will not work. Likeweise if the inverter is stronger than 
the counter the 13-15 link will not work anyway. Long story short - if 
it works, depends on actual chips used, year, maker. Short story shorter 
- bad design.

When you say something works once and then needs power cycle, all I'm 
thinking of in latch-up condition. Could happen if you force output or 
input above supply level. Is that inverter supplied from 12V too? Unless 
the cap in the input is like 10uF or so. I'd put 100n max there.
Maybe try to replace the inverter with a transistor and leave the poor 
pin 13 alone. You could even make whole reset conditioning circuitry 
with one transistor.

Roman

W dniu 2024-06-22 o 00:01, denshi via Synth-diy pisze:
> im trying to add a reset to a CD4520 but running into an issue:
>
> in the TKB serge uses a CD4520 to handle the vertical clock (cycling 
> between four vertical rows of pots)
> here is a relevant snippet of the schematic (as found on hyperreal)
> i copy and pasted the clock input to use as the “vertical reset” and 
> am sending that to an inverter to the bottom half reset - it works, 
> but only once, and then not again until i power cycle. am i missing 
> something simple here?
>
> Inline image
>
>
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