BeamBreak Detector based on Liftmaster 41A5034 Garage Door Opener Safety Beam Kit
I have a Liftmaster 41A5034 Garage Door Opener Safety Beam Kit that I bought to replace an intermittent sender on one of my garage doors several weeks ago,
from here.
I hooked up the sender and receiver to a simple dc power supply tonight, and made some basic measurements. I was reliably able to get a range of >30ft. They operate on ~6Vdc, at low current. The receiver puts out a pulse train when illuminated as shown on the movie (not a simple dc level). I am designing a simple interface to pull-in a relay or drive a SSR when the beam is broken, and will post it soon.
To figure out how to wire this up, I had to get out a ladder, and find the Thevenin Equivalent of the power supply inside the Garage Door Opener. That is where the 6.3Vdc open circuit in series with a 51Ω resistor came from
ps- here it is the circuit. It will drive either a 5V relay, or a Solid-State-Relay. It requires a small DC power supply, could be a surplus DC Wall-Wart ,a 6V Lantern Battery, or 4 D-cells.
As long as the beam makes it from the Tx to the Rx, the Rx pulses its wires such that it pulls the voltage across it to near zero Volts. See the red trace V(wht-blk) in the simulation. If the beam is broken, the Rx stops pulsing. The 51Ω resistor R1 provides a load resistor across which the pulse appears.
To actuate a relay or SSR, I had to detect the cessation of the pulses. I'm using a 555 as a re-triggerable monostable; each pulse resets the timing circuit, see green trace V(rc). A few mS after the beam is broken, after the last pulse in the stream of pulses, the voltage at V(rc) rises to allow the output of the 555 blue trace V(out) to switch low, pulling-in the relay or turning on an SSR. If you use an SSR in place of the relay, you can leave out the snubber diode D2.
V3, the DC power supply is not particularly critical; anything from 5Vdc to 8Vdc will work. I used an old 5.5Vdc cell-phone wall-wart charger...