TIL: A garage door button is just two wires touching (Garage Door Project, Part 1/5)

Series: Opening my garage door with my phone — Part 1 of 5 Learned: 2–4 July 2026

I can open my garage door with a remote. I wanted to open it with an API call instead. I know how to write the software, but I had no idea what electronics sit between “HTTP request” and “door moves”. This post covers the first few days: figuring out the hardware, digging through an old microcontroller kit, and getting a relay to click on my desk.

1. The opener only needs a “dry contact”

The wall button on a garage door opener doesn’t send any power anywhere. It just shorts two low-voltage terminals together for a moment. That’s called a dry contact.

So the whole “smart” part boils down to: something that can briefly connect two wires when told to. That something is a relay.

• Wire the relay’s COM (common) and NO (normally open) terminals in parallel with the existing wall button.
• When the relay closes for ~0.5 s, the opener thinks someone pressed the button.
• The existing remotes and wall button keep working. Nothing is replaced, only added.

Optional extra I’ve parked for later: a magnetic reed switch on the door frame to know whether the door is actually open or closed.

2. Inventory what you already have

I had an old kit from Hobby Components lying around. Relevant finds:

• Arduino Uno (clone)
• Keyes 5V relay module with three pins: S (signal), + (5V) and - (GND), plus three screw terminals: NC, COM, NO
• Arduino Prototype Shield v5, a board that stacks on the Uno for soldering your own circuit onto

What I learned: the Uno has no networking at all. To expose an API you need something with Wi-Fi or Ethernet. The options were:

I chose the last one: an old Raspberry Pi as the brain and the Arduino as the muscle. (Spoiler: the Pi being old became its own adventure, see Part 2.)

3. Wiring the relay for a bench test

Before touching the garage at all, test on the desk with the Arduino plugged into the computer.

Leave the COM/NO screw terminals empty during the bench test.

What I learned: many of these cheap relay modules are active LOW: writing LOW to the signal pin turns the relay on. So the sketch starts by writing HIGH to keep it off.

const int relayPin = 7;

void setup() {
  pinMode(relayPin, OUTPUT);
  digitalWrite(relayPin, HIGH);   // relay off (active LOW module)
  Serial.begin(9600);
}

void loop() {
  if (Serial.available() > 0) {
    char c = Serial.read();
    if (c == 'o' || c == 'O') {
      digitalWrite(relayPin, LOW);  // "press the button"
      delay(500);
      digitalWrite(relayPin, HIGH); // "release"
    }
  }
}

Open the Serial Monitor at 9600 baud, type o, press Enter → click, click. The little LED on the relay blinks with it.

Bonus check: put a multimeter in continuity mode across COM and NO. It should beep for exactly the half second the relay is closed.

4. The detour: Johnny-Five and Firmata

My first instinct as a JavaScript developer was to drive the board from Node.js with Johnny-Five. It timed out.

What I learned: Johnny-Five needs the StandardFirmata sketch uploaded to the board first (File → Examples → Firmata → StandardFirmata, the plain one, not the Plus version). Without it the computer and the board don’t speak the same protocol. In the end I didn’t need Johnny-Five at all, because a ten-line sketch listening on serial was simpler.

5. “programmer is not responding”

Uploading anything to the Uno failed with:

avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 1 of 10: not in sync: resp=0x00

This means the computer is shouting down the cable and the board isn’t answering. The checklist that helped:

• Pick the right port. On a Mac, ignore Bluetooth-Incoming-Port; look for /dev/cu.usbmodem… (or /dev/cu.wchusbserial… on clones).
• Use a data cable, not a charge-only one. Lights turning on prove nothing.
• Take the shield off and upload to the bare Uno first. A stacked shield can interfere with the serial pins.
• Close anything else holding the port: the Serial Monitor, or a Node script still running in another terminal.
• Clones may need the CH340 driver.

6. Soldering is optional (for now)

The Arduino pins are small and I was nervous about bridging two of them with solder. Alternatives that are perfectly fine for this phase:

• Female-to-female / male-to-female jumper wires straight onto the header pins
• A solderless breadboard (great for testing, less great long-term in a cold garage)
• A screw terminal shield: strip the wire, tighten a screw, done

Takeaways

• A garage door opener’s button input is a dry contact. A relay across COM/NO is all it takes.
• An Arduino Uno can’t do networking on its own; decide early what provides the network.
• Cheap relay modules are often active LOW.
• Bench test first: Serial Monitor + listening for the click + a multimeter on COM/NO.
• “programmer is not responding” is almost always port, cable, shield or a busy serial port.

Next up: getting a first-generation Raspberry Pi onto my network, which took far longer than the electronics.