Garage door control

All you need is an isolated relay. Use the Master's relay to open and close the isolation relay which in turn makes or break the garage door control wires on the unit or at the wall control station. The garage door just needs the 2 OHD control wires to be shorted (closed) for a second or two. You should also get commercial alarm contacts http://www.grisk.com/surface_mount/4400.htm to determine the open or closed status of the doors. Contect the contacts to the security system if that's connected to AMX otherwise connect to an I/O.

any relay that maintains while control voltage is applied. The GDOs are most likely 24VAC and very low current so the load side of the relay just has to parrallel the push button either at the push button or on the GDO it self. Just make a switch on/off or open/close. Just use the master's 12vdc through a relay port. Find a relay that requires low control current. You should be able to find some as low as 15ma.

I'm pretty sure that relays don't add any voltage and simply close the connection. If you need power you'll need to add a power supply somewhere in the circuit. What may be confusing is that relays are rated for how much power they can safely pass-through and sometimes they are rated at what voltage is needed across the coil to active it (ie SPDT)

I would try manual touching the two wires at the garage door opener together to see if it moves. If it does, I don't know any reason a simple really wouldn't work exactly the same.

PeP_SD wrote:

Is it normal that I don't get any voltage when I measure it between A and B for channel 1??

Yes. If you had voltage I'd start to worry. The relay is a normally open dry contact which means that there is no power and if you put an ohm meter across the A & B terminals you will get infinite resistance. This is the OFF state. When you do a ON command from control devices you should get a short or 0 ressitance between the A & B terminals of the relay port being controlled.

This basically acts as a switch. Open or closed which will either impede current flow through a circuit or allow it.

Each relay can switch up to 24 VDC or 28 VAC @ 1 A

If you find the specs on your GDO I'm sure you'll find the control voltage that runs to the GDO button is 24Volt AC or just put a tester across the button and see what it is. I can't imagine the current being 1 A or more so if you wanted it's quite possible you could hook up two wires to A & B of a relay port and connect it to the wires on the back of the GDO button or unit. A parrellel connection.

Should the voltage or current be higher than that specified for the relay port or somehow the OHD guys while servicing the unit does something stupid you may cooked your port so when doing this sort of connection I will normally add a relay for isolation purposes. See attached picture.

The picture shows the OFF state of the relay port and the normally open state of the isolation relay!!