- Jan 1, 1970
after switching off, i mean. the main symptom apart from overheating is
the 393 can't pull down the A1 and B2 inputs of the 4538 any more - it
goes down to 10.63V and no further. With the 4538 disconnected, it works
fine, switching between 0V and +12V.
1. What are you using for Vdd?
2. Are you using 4538's or 74HC4538's?
3. You could be frying the 4538 because you don't have Schottky diodes
across the the timing resistors (cathode to Vdd) and the solenoid is
pulling the supply down, allowing the timing caps to dicharge through
the chip's protection diodes (yes, the dreaded parasitic SCR's rear
their ugly heads...)
BTW, did you get the circuit I emailed you?