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Re: How to use Liftmaster garage door IR safety sensors for other uses?

I know this is an old thread, but I actually measured how the ones on my Li=
ftmaster Pro 1/2HP model work. The main unit outputs 6.2V open circuit whic=
h dops to 5.84 when both sensors are connected. The total draw is 15 MA, in=
dicating the internal pullup resistor is about 25 Ohms. The transmitter and=
 receiver each draw about 7.5MA. In normal operation the transmitter sends =
out about .4MS pulses at about 160HZ. When the receiver sees them it pulls =
the supply lines to about .25V. This develops a signal across the main unit=
 internal resistor. The main unit needs to see these pulses in order to ena=
ble door closure. The yellow LED on the back of my unit flashes once about =
every 8 seconds then the sensors are disconnected and when you hook them up=
 and the unit senses the signal, it flashes 4 times.

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