Help.
I'm building a simple counter to control 4 Reed Relays. 2 of the relays break 1200Vac and the other 2 break 30Vac. The counter (74LS93) is used With Inverters & NAND gates so that by repeatedly pressing the (debounced) start button, the circuit loops through 5 states; OFF, Relay1 (HV), Relay2 (HV), Relay3 (LV), Relay4 (LV), Reset.
Everything works perfectly... until I turn on the HV supply and then the sequence goes errattic. I thought it could be noise so I moved the relays into a separate earthed metal box but it made no difference
To eliminate any leak-back into the control circuit, the HV Relays have a separate 24V supply and are activated by photocouplers & FETs so this circuit has no electrical connection to the TTL counter circuit.
I'm sure there is something blindingly obvoius I'm missing. any ideas...?
Ta Much
Mike.
I'm building a simple counter to control 4 Reed Relays. 2 of the relays break 1200Vac and the other 2 break 30Vac. The counter (74LS93) is used With Inverters & NAND gates so that by repeatedly pressing the (debounced) start button, the circuit loops through 5 states; OFF, Relay1 (HV), Relay2 (HV), Relay3 (LV), Relay4 (LV), Reset.
Everything works perfectly... until I turn on the HV supply and then the sequence goes errattic. I thought it could be noise so I moved the relays into a separate earthed metal box but it made no difference
To eliminate any leak-back into the control circuit, the HV Relays have a separate 24V supply and are activated by photocouplers & FETs so this circuit has no electrical connection to the TTL counter circuit.
I'm sure there is something blindingly obvoius I'm missing. any ideas...?
Ta Much
Mike.