Good question!Bob,
I have a question for you and I am sure you did it your way for a reason, but I wanted to know why to better help me understand circuits.. Take a look at my .pdf... What would happen if we eliminated the lower 555 and tied the diode in this way?
Woke up this AM wondering the same thing.
With the 555 configured as a "one-shot" monostable, there is the need to either re-trigger the circuit or power it down to effect a reset.
I haven't breadboarded these circuits (SIM only) but I'm confident they work. My concern was the transition time of the DPDT switch (the "off" period during the CW and CCW selections). I am uncertain that there would be an adequate power-off period for the 555(s) to "reset" and again produce the delay pulse.
I tried this in the SIM:
It took a minimum 150ms Timed Switch duration (thereby turning off power to the rest of the circuit) to effectively reset the 555. Any shorter duration failed to produce the reset. Of course, some of this time may have been a result of the inherent SIM speed. I don't know thw transition speed of the DPDT switch. I'll test a real switch's period later this morning.
Anyway, in the meantime, there's certainly no harm in wiring it as you suggest and trying it out.
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