Tech Forum

When you look across either sensor you will see negative going pulses. When the beam is broken it changes to supply voltage, no pulses. If you would like a schematic to "hack" this information send me a request. It is essentially a missing pulse detector.

All openers are not the same, but most are similar. You want to see when the beam is obstructed when the door is open, but you really only need to know when the beam is broken because if the door is closed, nothing can enter to break the beam. You can install an end of door travel switch in series with the relay if you like. With the beam intact, a scope shows pulses going toward ground but not to ground. A broken beam stops pulses and voltage remains at maximum.

When you look across either sensor you will see negative going pulses. When the beam is broken it changes to supply voltage, no pulses.

I used a LM555 because it contains differential amps to monitor voltage levels and will source or sink to 200ma. If your pulses go down to 1/3 of supply.. circuit with diode input will work ... if not, use transistor input. Any general xsistor, such as a 2N2222, will work. I'll stop here, but feel free to ask questions!

This will vary from one garage door opener to another, but most that I've seen have an LED either on the photo beam receiver or on the opener itself that illuminates when the beam is intact. If I wanted a relay to trigger, I would tap into this LED. If you want to interface to it without modifying anything, a phototransistor or CdS cell could be mounted over it to detect light from the LED. Anything else will require some reverse engineering on your particular opener.