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Simple on delay relay circuit?

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danrogers

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Hi all. I want to make a very simple circuit to add a 2-3 second 'on' delay to a power supply application.

I basically want to trigger with a 5v input, wait x amount of time then turn on the relay until the trigger signal goes.

I bought a unit off ebay thinking it would meet the requirements but it actually is a power off delay circuit. I'm wondering if the item I bought could be inverted somehow to do what I need?

https://www.ebay.co.uk/itm/5V-30V-M...er-Control-Module-Trigger-Switch/132786503131
 

Diver300

Well-Known Member
Most Helpful Member
That might work. It will work if:-
1) 100 kOhms will provide enough current to trigger the relay module.
2) The capacitor gives enough time for what you want.
3) The relay module will still trigger cleanly if the input rises slowly.
 

danrogers

Member
That might work. It will work if:-
1) 100 kOhms will provide enough current to trigger the relay module.
2) The capacitor gives enough time for what you want.
3) The relay module will still trigger cleanly if the input rises slowly.
Thanks Diver.

I guess maybe I should try and breadboard something up. Any tips on initial component value selection?

Thanks!
 

crutschow

Well-Known Member
Most Helpful Member
I bought a unit off ebay thinking it would meet the requirements but it actually is a power off delay circuit. I'm wondering if the item I bought could be inverted somehow to do what I need?
That module appears to be a standard 555 timer configured as a one-shot.
If you can trace out and draw a circuit diagram of the PCB, we can suggest how it can be modified to do what you want.

I don't think your circuit in post #2 will work.
That will just delay the start of the one-shot pulse.
 

crutschow

Well-Known Member
Most Helpful Member
Here's an example of a 555 timer configured to give a delay upon power application.
You may be able to modify your module similarly.

1540915296536.png
 

danrogers

Member
That module appears to be a standard 555 timer configured as a one-shot.
If you can trace out and draw a circuit diagram of the PCB, we can suggest how it can be modified to do what you want.

I don't think your circuit in post #2 will work.
That will just delay the start of the one-shot pulse.
Hi there. OK thanks, I will have a closer look at the module soon as I have a spare minute :)

RE. my circuit I was actually thinking of just using a standard relay module for that (active low) and ditching the 555 module.
 

crutschow

Well-Known Member
Most Helpful Member
I was actually thinking of just using a standard relay module for that (active low) and ditching the 555 module.
That should work if the relay module has a high input impedance.
It wont' work with just a relay.
 
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