How it works

The hardware is very simple, the shield has a small relay, a diode, 2 resistors, a momentary button that links D3 to GND (new in R2) and a 2.1mm barrel jack for optional power (new in R2). The 8 pin header has connections for 2 hall effect sensors and the door opener. I used a female header to connect an 8 wire cable to the two sensors. One sensor is for the open position one is for the closed position. That way you can tell whether the door is open, closed, or stuck somewhere in between. The other two wires are a contact closure driven by the small relay to trigger a door action, and are connected directly to the garage opener. This is equivalent to operating the garage from the regular door opener, and thus GarageMote does not interfere with the normal garage door operation.
The relay requires more current than one pin can supply and hence is driven by two digital pins (D6+D7). Pin D4 is the output from the “OPEN” hall sensor. Pin D5 is the output from the “CLOSED” hall sensor. The diode protects against the inductive kickback from the relay coil.