Need a simple relay delay circuit

Thread Starter


Joined Aug 30, 2013
I need a circuit or module that does the following:

When a switch output goes high it triggers a timer to output 12VDC for about 2.5 seconds. The key is that the timer needs output a high for 2.5 seconds and then turn off even if the switch output is still high. The timer only resets when the switch output goes low.

I'm sure there is a easy solution. I just don't know how to search on what I'm looking for.

- Allen


Joined Jan 15, 2015
You are describing a "One Shot Multi-Vibrator" also called a Mono-Stable Multi-Vibrator. These come in a few flavors so you may want to give
What is the difference between a nonretriggerable and retriggerable One Shot? a read. What you want is when triggered a single output pulse of a 2.5 second duration regardless of a change in trigger state. You can either build (roll your own) or buy a relay timer circuit to do what you want. A Google of relay timers should get you a dozen hits. That or Google One Shot Relay Timer and that may narrow things down.