Odp: [sdiy] crazy CMOS behavior

[mark verbos]

As it turns out, the problem was related to the load input. I am using 
an analog switch to decide if the trigger in is going to the step input 
or the load input. I had to tie both to ground with a resistor so when 
the switch is the other way they won't "float". I was using a 456k 
resistor (it's what was laying around) and I guess it wasn't strong 
enough to keep the load input from floating, because it was.

My question is, what value is enough to keep it down, but not too much? 
Do I need to switch between the trigger in and ground? That would result 
in a PCB change, that I hope to avoid.

thanks...

mark




Roman wrote:

>probably your CMOS inverter is oscillating because it is driven with
>too slow transients. RC network driving transistor will cause such
>slow changes. You can use smaller cap, or better - schmit gate
>40106, or 4006, can't remember the name.
>
>Roman
>
>----- Original Message ----- 
>From: mark verbos <a0284520 at addcom.de>
>To: synth DIY <synth-diy at dropmix.xs4all.nl>
>Sent: Wednesday, October 02, 2002 7:30 PM
>Subject: [sdiy] crazy CMOS behavior
>
>
>>I have built a sequencer based on the 4516 counter. The clock input is 
>>stolen from the Serge TKB schematic that is on music machines. That is, 
>>trough a cap to an NPN then a CMOS inverter then to the counter. When I 
>>clock it, with anything, it jumps all over the place with no real sense 
>>or pattern. Could this be related to the step length not being right? 
>>How does it work for the actual Serge? It's not the chips, I have 
>>switched them all out and it does the same tihng. Am I just missing 
>>something not grounded or something?
>>
>>thanks for any ideas, I'm going nuts here.
>>
>>mark
>>
>
>