gEDA-user: challenge board ALMOST works

[Samuel A. Falvo II]

On 9/10/06, DJ Delorie <dj at delorie.com> wrote:
> However, the two oscillators tend to self-synchronize.  If I let it
> run, one LED is on and the other is off.  If I put scope probes on the
> buffered outputs (pins 6 and 8), I can see that the oscillators are
> running, they're just in lock-step.  Not even out of phase.

I think you accidentally re-discovered the "synchronous oscillator."
Since all your inverters are on the same physical chip, the output of
one is likely influencing the other just enough to result in
synchrony.

> Ideas?  The only thing I can think of is inductive or capacitive
> coupling, but at 400 Hz?

Even at such low frequencies, sharp transitions cause differential
spikes to appear on adjacent wires, and it's possible that those
perturbations can still cause circuits to interact.

Ahh ... the life of an analog circuit designer.  :D

-- 
Samuel A. Falvo II