Advice on a relay/timer or other device I can use

Hilton Janfield's picture


Joined: Feb 12, 2021

Replies: 0
Advice on a relay/timer or other device I can use
February 12, 2021 - 7:09am

Not sure where to put this, or if this is even an appropriate site. I'm looking for some help to identify a timer or other module I can use to control a circuit. I'm trying to normalize operation to various pieces of equipment (a couple dozen for now, a couple hundred in the long term), wth several different connection types and behaviours to input.

One trigger connection (SPST button, which has typical NC/NO/C contacts), unpowered.

One powered circuit to be controlled (+5VDC). In most applications the circuit is NO and must be closed to activate the device - but in some cases it is NC and the circuit must be broken instead. One or more other switches are usually also connected to the same contacts, so in the latter case the module will be wired in series.

I'm guessing I am also going to need external power for the timer/relay. This is where it gets difficult. The various equipment I am connecting to has different power contacts available. There MAY be a 5VDC power source. There is LIKELY to be 12VDC in most of them, but not always. Some are powered from 16VAC or 18VAC I can't recall which, but I think those ones also have 12VDC available. There is usually (but again not always!) 120VAC coming in, but I want to avoid transformers if possible as I need to keep cost as low as possible for dozens of installations. There is one other potential power source I could use, but I'd rather not - the switch is mounted inside of an electronic lockbox which uses two CR123A batteries, so I could potentially pull 3V or 6V from there. However, the life of these batteries is normally 3-10 years (depending on location and usage) with routine replacement at 5-6 years and I'd rather not impair that.


I've managed to come up with a single program path that will operate ALL of the numerous connections and input behaviours the way I want, while eliminating most of the issues that could actually have.

  1. The button is normally OUT. Do nothing when the button is OUT. Wait for button IN.
  2. When the button goes IN, do nothing, but start a timer.
    • If the button stays IN for more than a set amount of time (probably 2 minutes), we need to follow a different route:
      • Do nothing until the button comes OUT again and stays that way for at least 2 minutes, at which point we can reset to step 1.
  3. When the button comes OUT again:
    • Activate the relay circuit for 5 seconds only (open or close circuit as needed, then reverse).
    • Return to step 1.

Without step 2, almost any timer relay that I've found will do the job. But step 2 protects against idiots and is unfortunately needed.

Sourav Gupta's picture


Joined: Feb 12, 2018

Replies: 696

Your question is somewhat confusing. Could you share your thoughts in a paper with some block diagrams? Just showing input outputs and workings?

You can also attach ppt if you have.