I am trying to design a two stage timer circuit using off the shelf components which I have already chosen. The idea is simple. The first stage is a digital display countdown timer that triggers the second stage. The second stage timer is a fixed run time timer module. The second stage is triggered with a momentary or continuous connection of the "on" terminals. The "on" terminals are voltage isolated from the module. It is commonly called a single shot timer.

Both timers operate on 12VDC.

Here is the problem. The first stage timer has relay contacts (spst) that are closed when the timer is running or "counting down", the contacts are open when the timer is on standby or powered off. When the countdown is completed the relay contacts open. I need the first stage timer to do the opposite. When the "countdown" is finished (the delay) I need it to signal the second stage timer to start with either a momentary or continuous connection.

Here are the links for the two timers:

Dwyer Instruments - Series LCT316


Single Shot Products (see the "TGP" series)

In addition I have a 12VDC power supply.

I just need to hook them up so the countdown timer (dwyer) triggers the single shot timer module (airotronics) when the countdown timer reaches "0". This will allow a variable delay in the start time. Then the timer module would run for it's preset time. Perfect, except the countdown timer doesn't have the proper relay contacts (spst) . There must be a simple solution but I am to inexperienced to figure it out.

Thanks
Scott

 

Re check specs on TGPS, if you do not already have the timers. Sounds like a perfect match, triggers on opening of switch. If none of that applies, you can add a third relay to invert switch operation. Thirdly, check for voltage on switch input contacts; might be able to use a transistor switch interface although would not be off shelf.

 

Thanks Bernard!