Basic circuit - 12v trigger to momentary relay?

ScoobyDoo69 · 28 Mar 2021 at 18:37

Hey guys,

Not sure if this is the right place for this, but I need some help with some basic circuitry as I haven't a clue.

My projector screen doesn't have a 12v trigger input, but it does have an RJ12 cable with Common, Up, Down, Stop. Touching down and common drops the screen, up and common takes it up.

What I want to be able to do is take the 12v trigger from my amp or projector when turned on, have it hit a relay which in turn closes down/common for a few seconds then disconnects (even whilst 12v remains). Then once 12v is removed, close up/common for a few seconds and then disconnects.

This is just a simple circuit like the below right?
https://www.ebay.co.uk/itm/DC-12V-T...mer-Relay-Module-High-Power-30A-/252983832379

Any pointers would be appreciated

Thanks

wesimmo · 28 Mar 2021 at 19:14

I don't know exactly what you just said...but an arduino board might do what you want?

ScoobyDoo69 · 28 Mar 2021 at 19:19

Arduino seems a bit excessive for what I'm hoping can just be achieved with a basic relay.

Flake87 · 28 Mar 2021 at 20:25

Perhaps something like a plug in relay would do what you want?

https://www.foxtamcontrols.co.uk/products/14-pin-4pco-delay-on-timer-multi-time-range

mushtafa · 30 Mar 2021 at 23:18

Does the connection (common/up common/down need to disconnect every time?

If not, a common 5 pin relay would be sufficient.

If the connection needs to be open again, you'll need to incorporate a timer of some description.

ScoobyDoo69 · 31 Mar 2021 at 08:30

A split second connection with common or up/down triggers the screen to do what it needs to do. I can't confirm whether it needs to be open again, but for peace of mind regarding the motor and any randomness I'd rather it opens again.

Adam_151 · 31 Mar 2021 at 14:11

Do you have unswitched 12v from the projector as well as trigger. I.e. 3 lines +12v, 12v trigger, ground ? Or just the two?

I 'think' it would be possible to do without an external power source if you only had the two, but it adds complexity that you wouldn't have otherwise. Or is an external power supply being requried not a problem?

ScoobyDoo69 · 31 Mar 2021 at 17:28

I believe the 12v trigger is just the two as most people just use a mono 3.5mm jack.

The 12v is "on" as soon as the projector is turned on, and "off" as soon as projector is turned off.

mushtafa · 31 Mar 2021 at 20:57

Very crude pic done in paint. This simple 5 pin relay would work, but would always keep the contacts connected. I'm still thinking of a way to make it momentary

mushtafa · 31 Mar 2021 at 21:03

https://www.ebay.co.uk/itm/DC-12V-A...rn-Off-Switch-Time-Relay-Module-/252573399329

Something like this might work. Looks like it'll disconnect the relay after a set time

ScoobyDoo69 · 1 Apr 2021 at 20:14

I had looked at that exact one, but had no idea whether or not I was barking up the right tree!

For the price I guess it's worth a punt!