Greetings! I built your Time Delay Relay using a 556 chip to control two relays. Everything is working as indicated, however, I was hoping that the trigger could be on longer than the timed delay. Let me explain. I'm triggering the chip with an external SPDT NC relay within another device. The NC feeds one side of the 556 and the NO feeds the other. Regardless of what state the SPDT relay is in, I would like the time delay realys controlled by this circuit two be energized for about two seconds, no matter how long the trigger is on. What I'm experiencing is that a momentary trigger will activate the realy with the desired delay, or a long trigger will keep the relay on for the trigger time plus the delay after the trigger is removed. Perhaps I'm asking this circuit to do something it was not designed to do? I appreciate any input! Rod
The 555 and 556 do not time-out if their trigger voltage is held low. Some of their datasheets show how to use a coupling capacitor and a resistor to the positive supply to create a negative-going pulse to trigger the timer but then it goes high even if the input is still low.
Time Delay Relay
Posted - Jul 09 2010 : 11:42:27 AM
