From the Q&A

With TJ Byers

Sequence Timer

Question:

I’m looking for a circuit that would provide a cascaded string of 10 timers with different delay off and on times. Each stage would consist of two timers: one for delay and one for power on. I’d like each timer to be pot adjustable from 2 seconds to about 5 minutes. As a final request, I’d like to have a switch which would enable me to route the output of the final timer so that it could start the cycle all over again.

Don Fleshren
Sterling, VA

Answer:

This design is based on the 555 timer, and is relatively simple to construct and use. I only included two stages, but it’s easy enough to expand this to as many stages as you wish.

IC1 is the first delay timer. When it expires, it triggers IC2, which can now power whatever you want using logic output #1 to drive a transistor, relay, or other device. (Just for fun, I’ve connected output IC1 to an LED so that you can see where you are in the sequence, in case you get lost.) At the end of IC2’s cycle, IC3 is triggered, which now pauses for whatever time you set the potentiometer for, after which IC4 kicks in...well, you get the picture. If you want this to be recursive, simply provide a path from the last stage to S1. To reduce part count, use a 556 chip which contains two 555 circuits. If you need more precise timing you’ll have to go to a digital design.