Relay switch for 12v trigger

Thread Starter

Pseudomax1

Joined Mar 9, 2020
12
Hi,

Forgive the lack of technical language...

I have a reasonably straightforward project that I need some help with. I am creating a cinema room and I have a projector with a 12v trigger out which I am assuming sends a pulse out when it is turned on and a pulse when it is switched off. This is usually used to initiate the motorized projector screen up and down.

However, my projector screen does not have the 12v trigger adapter meaning I have no simple plug and play solution. Instead it has a 3-way switch connected to 110vac. Middle is off and rocking up or down raises or lowers the screen.

I want to take advantage of the 12v trigger on the projector and therefore need a relay for 110v that is triggered by the 12v pulse and cycles through the up and then down switch with a timed off happening after 1min or so...

Any relays or circuits you can point me to?

Thanks in advance...
 

Thread Starter

Pseudomax1

Joined Mar 9, 2020
12
Hi, I was wrong ... I get a permanent 12vdc output when switched on that then goes to 0vdc when switched off...

I suspect this makes things easier?!!
 

Jerry-Hat-Trick

Joined Aug 31, 2022
545
Presumably, if the projector is switched on the screen needs to come down and go up when the projector turns off. It sounds like there are limit switches to make it stop when it's either up or down if the switch is still held on. I think you could use a DPDT (Double Pole Double Throw) relay with 12V coil something like https://www.ebay.co.uk/itm/183739611156 (sorry, I'm on the side of the pond with higher AC voltage) with the coil energised with 12V wired to bring the screen down, so long as you are happy that the limit switches turn the motor current off in both directions. For clarification of DPDT switches scroll down the page at https://www.moz.ac.at/sem/lehre/lib/pd-sounddesign/switch.html
 

Thread Starter

Pseudomax1

Joined Mar 9, 2020
12
Thanks @Jerry-Hat-Trick ... I'll give it a try... although I'm not certain about the screen and the limit switches! I presume that if the screen stops drawing current with the switch on then that indicates a limit switch?
 

sghioto

Joined Dec 31, 2017
5,380
I want to take advantage of the 12v trigger on the projector and therefore need a relay for 110v that is triggered by the 12v pulse and cycles through the up and then down switch with a timed off happening after 1min or so...
Here's an analog dual timer circuit using an opto-isolator for the 12 volt trigger input.
1670976494734.png
 

Thread Starter

Pseudomax1

Joined Mar 9, 2020
12
Here's an analog dual timer circuit using an opto-isolator for the 12 volt trigger input.
View attachment 282976
Hi @sghioto , thank you for this... it looks great... and if you have designed this specifically for my application then even more appreciation!! My issue is that although I am handy with a soldering iron and know the principles, I am not skilled in the detail... so can you direct me to somewhere I can go to learn about interpreting the schematic and the various components? I know what the resistor nomenclature is and switch circuitry but I am somewhat less knowledgeable on the other parts of the diagram!
 

sghioto

Joined Dec 31, 2017
5,380
And another version using the 12 volt trigger to power the circuit when the projector is ON.
9 volt battery powers the circuit only when the projector is OFF to raise the screen. Standby current practically zero in this mode.
1670980038125.png
 

Thread Starter

Pseudomax1

Joined Mar 9, 2020
12
A further update...

I checked the screen for a limit switch and I am reasonably sure that the screen is fitted with one. When I reach to each limit the multimeter (an old analogue one) goes from 110vac down to a small reading (that does not change when I change the dial from higher to lower scale... perhaps that makes sense to someone?) ... and the current draw seems to drop to 0mA although my meter is not rated for the current and after a couple of test I blew the fuse... but the first couple of tests operated the screen and went to 0 after the limit reached. So let me know if this confirms the presence of limit switches?

Thanks in advance...
 

Thread Starter

Pseudomax1

Joined Mar 9, 2020
12
And another version using the 12 volt trigger to power the circuit when the projector is ON.
9 volt battery powers the circuit only when the projector is OFF to raise the screen. Standby current practically zero in this mode.
View attachment 282991
Again really appreciate the effort in sending this!!!

With my concerns around limit switches; I think it might be better to use your suggested board schematic that you have provided (along with enjoying learning how to create it...), but I will again need to know where to be directed to read up on the schematic...
 
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