I have a (to me) strange issue. I have a small circuit that needs to send out a set of small pulses from a push of a button. I have created two 555 timer circuits (using a LM556) where one is a momentary switch with about 1 sec hold time, and the other is approx 100Hz which is supposed to turn on ONLY when the output signal from the first timer is high. See the attached diagram.
First of, this setup works albeit it took quite a bit of experimentation with the Control Voltage.
Problem: When I don't use the switch, after a bit of time (5-10 seconds) I get a pulse about every second from the second timer - even though there's no signal coming out from the first timer (U1A). I found that adding a small resister in parallel with the D1 LED would fix this (not sure why) but if there's another circuit that turns on an LED for instance, somehow that triggers a single pulse from this circuit too.
I'm sure I'm overlooking the obvious? I just cannot see it.