I should probably subtitle this “How I Broke My Warranty.”
Like many people that bought Linear’s GD00Z-4 “Garage Door Opener Remote Accessory,” I was surprised when it refused to open my garage door. How could it not work? It shows up in my SmartThings app. The position sensor works when I manually move the door. When I send a command, the beeper beeps and the strobe light flashes. Yet my garage door remains stubbornly still.
To make things worse, when I remove the wires from my opener and clip them to my continuity tester, then press the button in my SmartThings app, the tester beeps! Put the wires back on my opener and it doesn’t work again. Just confounding.
First I want to say “thank you!” to everyone that posted about the 60 second delay. Apparently there is a law which requires this type of device to wait at least 30 seconds between operations. It appears that Linear has chosen to wait 60 seconds or so. Your posts saved me a bunch of grief trying to figure out that one.
Then I read a few threads where the GD00Z’s wires were connected to the pushbutton of a wireless remote, which then operates the door. Another variation is connecting the wires to the coil of an external relay, which was then used to operate the door. This made me believe that Linear’s relay (either mechanical or solid state) wasn’t “strong” enough to handle the load.
So I popped open the GD00Z-4 and found a mechanical AZ957 Subminiature PC Board Relay. This little guy is UL rated at 1A max at 30V DC! For fun, I measured the current used by my opener when shorting its wires and found it was only 50mA. There is just no way the GD00Z-4 can’t operate my opener.
After a little investigation I discovered that the GD00Z-4 monitors the relay contacts to see if it’s connected to an opener. If it doesn’t detect some minimum amount of voltage then it does not activate the relay. Here is a simplified schematic of the “Contact Monitor” (my words).
As you can see, an external voltage applied across the contacts is run through a full wave bridge. This makes the contacts polarity insensitive. The rectified voltage is filtered by a small cap and fed to the base of a transistor. The transistor then switches the test point “SS” to ground.
So I looked at test point “SS” with my 'scope. When my continuity tester was connected to the GD00Z-4, SS was a steady low (close to 0V). When my garage door opener was connected, SS was low with high going pulses. I looked at my door opener with the 'scope and noticed that the 5’ish volt signal had bursts of noise every 250ms. When I zoomed into the noise, I could see they were little packets of communications data roughly 20ms wide.
Now I had a theory – the “noise” of the communications traffic was preventing the GD00Z-4 from working. And I understood something – the reason the wireless remotes and external relays work is because they isolate the GD00Z-4 from the communications “noise.”
I decided that if I could force test point “SS” low then the GD00Z-4 would work. I could have tried to remove the “noise” by adding a bigger filter cap, or forcing the transistor into the “on” state by lifting the base resistor and applying a fixed voltage to it. But knowing that the transistor just shorts SS to ground, I decided to simply do that. . .
As you can see, I soldered the white jumper wire from test point “SS” to the “COM” test point. The “COM” test point is circuit ground. And. . .
Now for the full disclosure part. My opener is a Raynor branded LiftMaster. I did not buy the MyQ option. My wall button does have the motion sensor and controls for options like automatically closing the door, etc.; but, I do not use any of that. I have not tried to see if the motion sensor or any of those other options still work. I only use my wall button as a button. And that still works, so I am happy.
Obviously, I’ve voided my warranty (for sure on the GD00Z-4, possibly on the door opener?). I was willing to risk permanent damage to both my GD00Z-4 and my door opener in this experiment. I’m posting my findings here for your entertainment. I was super curious to understand why the GD00Z-4 wouldn’t work with my opener. Now I understand, my curiosity is quenched, and hopefully yours is too.
TL;DR – Shorting test point “SS” to ground seems to have let my GD00Z-4 work with my LiftMaster. Been working for a couple of weeks now.