garage door remote as plc input

I have some gate controllers that I want to give the owner a

way to open them out at the gate.

I bought two universal garage door remotes @ Radio Shack.

Here is the problem,

The panel only has 24VDC. The garage door opener, I believe is 12VDC.

I'm thinking I could make a voltage divider if I knew the circuits total resistance.

The input is to a Twido plc. I'm going to go and try and find the input card specs online right now.

I'm thinking of going and getting a potentiometer from Radio Shack to determine the resistor I need.

What size potentiometer should I start w/?

Am I on the right track?

ganutenator,
Resistors are not the way to go. You will need high wattage resistors, they will generate lots of heat (depending on value and the draw of the receiver), and they will load down your 24vdc power supply.

Instead, look at a DC-DC converter like the one at AutomationDirect.

http://web5.automationdirect.com/ad...(Electrical)/DC-to-DC_Converters/PSP12-DC24-2

It mounts on DIN rail, accepts 18-72vdc in, outputs clean 12vdc power at up to 2.0A, and is a much more elegant way to do things. People who service your rig down the road will thank you for doing it the right way.


Good luck,

-rpoet

OK here is what I understand
You want to control gates with Twido PLC.
You will have Radio Shack remotes to provide open close signal.

PROBLEM
Twido wants 24 VDC on inputs. RadioShack units are 12.

SOLUTION??
Use relay with 12 volt coil (controlled by Radio Shack)
Twido 24VDC input is switched by relay contacts.

Dan Bentler

The Twido PLC will work with 12Vdc signals.

I had a similar situation with gates where I was getting an auxilliary output from limit switches into the PLC and HMI, but as the site upgrade hadn't been completed by the client, this signal was still driven from the old 12Vdc supply that illuminated the LED indicators.

Jon.

It works, but how many code violations did I make?

I connected a 12VDC transformer + to the wire going to the garage door opener.

The return wire from the opener, I have going to the positive side of a 12-24VDC blue led which I believe implements a miniature step down transformer.

In parallel, I have jumpered a wire to the twido input card.

The negative side of the 12VDC transformer I connected to ground and the negative side of the led.

There is obviously some minute amount of current going from the 24VDC transformer to ground.

I am wondering if I should ground the 24VDC - terminal.

How bad is this?

additionally,

The customer is very happy that he has remotes for the gates now.

I am worried that my boss, when he arrives tomorrow, will rip it all out because I am jeopardizing his UL label.

thoughts?

I connected a 12VDC transformer + to the wire going to the garage door opener.

Click to expand...

You can have a 12VDC power supply.
You can have a 12VAC transformer.
But a 12VDC transformer, no.

Where did the 12VDC come from? I thought the panel only had 24VDC?
I'm going to assume you have a separate 12VDC supply in the garage door opener.

The return wire from the opener, I have going to the positive side of a 12-24VDC blue led which I believe implements a miniature step down transformer.

Click to expand...

I highly doubt there is a tiny transformer of any type inside that blue LED. More than likely it simply pulls twice as much current at 24VDC as it does at 12VDC, but both are within its specs.

In parallel, I have jumpered a wire to the twido input card.

The negative side of the 12VDC transformer I connected to ground and the negative side of the led.

Click to expand...

So basically, you put a light across the input, no big deal there. Has nothing to do with matching 12VDC signal to 24VDC input, but it doesn't hurt anything either.

If your 24VDC input will fire with only 12 volts, hooray! It's fine. It would be nice to know how many volts it takes to turn on the input so you could be sure it would be reliable. (i.e. if it turns on at 10 volts, you're good)

There is obviously some minute amount of current going from the 24VDC transformer to ground.

I am wondering if I should ground the 24VDC - terminal.

How bad is this?

Click to expand...

The 12VDC and the 24VDC common should be connected together. If they are both grounded at the same point, they are connected. If they are grounded in two separate locations, see if you can ground them together instead.

Jeopardizing the UL label? I don't think you have a UL label anymore on the garage door opener or the PLC panel.

If I had to so something like this, I think I would approach it like this. Try to minimize modifications to both systems. Don't directly connect them!

Wire a small relay coil to the garage door opener, have the coil pull in with the opener on its power (12VDC).

Wire an isolated contact from the relay to an input on the Twido using its 24VDC power.

Use a UL listed relay.

You may still not be 100% kosher with adding the relay to the garage door opener (its UL label), but you should be fine on the PLC panel.

You can probably even mount the relay in the PLC panel without causing trouble.

Now you don't have to tie the 12VDC and the 24VDC together at all. And no wires directly connect the garage door opener circuits to your PLC.

Why not use UL rated industrial wireless controls such as this.
http://www.controlchief.com/

http://www.controlchief.com/raymote.html

http://www.remotecontroltech.com/Applications/Applications.aspx

Using radioshack parts on a industrial control system could get you in hot water if there are ever any problems with the sytem or it is involved in an accident with people or property.

I could see this open partially then malfunction and start closing on someones car before it is clear.Just something to consider given the way things are these days.

Radioshack subsystems are for hobby and home use IMHO

So basically, you put a light across the input, no big deal there. Has nothing to do with matching 12VDC signal to 24VDC input, but it doesn't hurt anything either.

Click to expand...

It didn't work until I installed the led. Before installing the led, the opener wouldn't interrupt the 12VDC. As soon as I installed the led, the voltage was aprox. 5v with the switch off, and 12V when the switch was on.