Hack garage door opener Liftmaster 973LM

Hey everyone, totally new to Arduino/electronics in general.

So basically what I am trying to do remove the push button on the Liftmaster 973LM and use a relay to control it using an Uno. Only problem is that I have no idea how to set up the circuit. (Garage door opener runs on a 3 volt battery). I know I have to get a relay, resistor, diode, and transistor, but not sure on which ones to get (voltage/current).

My end goal once I get more advanced is to hook up a keypad to the Arduino and build a keypad entry device for my garage, but that's later down the road. Thanks for your help!

Place the relay contacts in parallel with the existing wall-mounted switch.

(see dwg attached.)

I did the same thing with my liftmaster opener this weekend.

Main components were Attiny84A, Keypad from Adafruit, Weatherproof alarm cover from Amazon, and a BC548. All my components were SMD to keep the size down.

After opening the opener up, it had one tactile switch and 3 additional open areas for tactile switches that were all on the same line. (I snipped off the tactile switch on final product)

Just the BC548 was all that was needed for me to activate the trigger to open/close the door. A relay would definitely work, but if your going to use a transistor to activate your relay, depending on the exact workings of your opener you may be able to go smaller with less parts by skipping the relay.

Also, running off batteries, the power consumed activating a relay coil versus just a transistor that only has to overcome the pullup on the openers circuitry will add up to a lot of savings.


A transistor could be placed at/near the rear panel terminals without tearing anything apart.
But that’s a lot for someone asking this question and being “totally new to Arduino/electronics in general” to get right.
By getting the relay clicking at the kitchen table, it’d be easy enough to lead the relay contacts (no polarities to observe) out to the terminals.
It could be big fun with a “relay shield”, too.

I don’t know if it’s supposed to be available selectively, sporadically, switched on as needed or ready at all times (battery powered v. line powered.)
What to do, yes?
“The best laid schemes o’ mice an men…”

Thanks for all the replies. I was able to succeed using an OMR-C-105H relay with a IN4001 diode. I found the two pins on the Liftmaster remote which open the garage when together and hooked them up to the relay. I don't need a transistor with this relay as the voltage/current are within the Uno limits. I slightly changed the code here: http://www.glacialwanderer.com/hobbyrobotics/?p=9.

I will pursue the route drobe011 took and use a transistor instead of the 5v relay and replace the Arduino with an atiny once I get the keypad. Drobe011, can you share some of your source code? I think we are trying to accomplish the same thing.

I would be happy to share all code, schematics, pcb layout and BOM. However, I do not use the Arduino IDE or its libraries to program the AVRs. (I do use the Arduino libraries for my Due though).

My advice would be to continue to study/experiment with C/C++ and Arduino’s twist on it. Have a plan for your code as well as your project and write your code in a way (ie document it well, use good structure/form, smart variable names, etc) that allows you to build upon it as you grow. Verify/validate in small blocks. When you hit a bump or what you might think is an obstacle, use it as a chance to rethink, research and retry. Then come here to the forum; share what you’re trying to do, what you’ve tried and what’s not working. Better to learn the how than the what.

I did the same thing as it seems you are doing. Prototyping on a larger frame (my case an ATmega1284P), see what your code size is when your done, then pick the appropriate chip or Arduino to use for the finished project. Then you still have your most likely more expensive prototyping board to start the next project.

I am in no way an expert or even know half of what I’m doing but if you need anything I may have for this project let me know.


Thanks Dave (drobe011) for the great advice. What I will do is get my hands on a keypad and try experimenting with it. I was able to use a transistor instead of the relay, so all I have to do now is using the keypad to make a security lock.