Advice needed on triggering a device that uses a GND trigger

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rsouthgate

9 posts

Wannabe Geek

#205414 12-Nov-2016 09:09

Let me try and explain the setup. I've got a gate opener logic board that has a 12v output for accessories. It has a terminal labelled 'swipe card' that is used to trigger the motors by an accessory. If I use a wire to connect the COM output for the accessory and this terminal it triggers the gates to open. The keypad has a normally open and a Normally closed output along with a shared COM. So if a correct code is put in the normally open output will switch to 5v for 3 seconds and the normally closed will drop from 5v to 0v for 3 seconds.

I had assumed that I could use the normally closed output and connect that into the 'swipe card' input and it would see the voltage drop, but it doesn't.

I could use a small DC 5v to 12v transformer if the logic board is expecting to see a greater voltage drop, but it doesn't make sense to me that I can trigger it by connecting directly to the common output... so nothing connected to the terminal but then grounding it - which doesn't seem the same as a constant 12v going to 0v.

Any digital electronics experts here that can tell what is going on from my limited explanation?

And before anyone asks, these were both bought from China with very poorly documented instructions which have not enlightened me at all!

djaggar

78 posts

Master Geek

Lifetime subscriber

#1668424 12-Nov-2016 09:54

If I understand you correctly, connecting the common on the gate opener to the trigger on the gate openeer works. So can't you just use the normally open terminals on the card reader to do just that ... i.e. commom to common and normally open (NO) to triigger?

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rsouthgate

9 posts

Wannabe Geek

#1668430 12-Nov-2016 10:16

Yes, that's right re your understanding, but no it doesn't work if I connect NO and Ground. Although in the instructions with the keypad it shows the three wires (yellow, black, red) as Power off Unlock(+), Ground line and Power on Unlock (+) and I'm assuming the red power on unlock is NO - is that right?

Does it matter that these are 5v instead of 12v?

djaggar

78 posts

Master Geek

Lifetime subscriber

#1668435 12-Nov-2016 10:27

I expect that something marked Normally Open closes a dry contact relay ... i.e. no "wet" voltage on it ... a multimedia should see those contacts short togther when triggered ... so no, voltage should not matter, or be involved at all. Are red, black and yellow the only connections on the keypad? That would normally indicate you should power it with red & black and use yellow as the trigger ... how exactly is it marked?

rsouthgate

9 posts

Wannabe Geek

#1668438 12-Nov-2016 10:36

There is another red and black marked as 12v power input. So I have the red lead of that one coming from a terminal marked vcc on the opener that is outputting a constant 12v. The black lead to that one from COM on the opener. A red lead from the 'power on unlock' of the keypad back to the swipe card trigger terminal on the opener and a black lead from the ground of the keypad outputs to the same COM on the opener

djaggar

78 posts

Master Geek

Lifetime subscriber

#1668446 12-Nov-2016 10:45

So don't you want power off unlock connected? i.e. pull the trigger input of the opener to ground just as you do when you trigger it manually? Just put a meter between the common and the two outputs of the card reader and see if one shorts ... and use that :-)