I picked up a couple pairs of these Liftmaster 41A5034 garage door safety sensors, which I thought I might be able to use for other sensing on my homebrew
home control system. Does anyone know what voltage/current the sender needs, and
what connections the 2 wire detector needs and how it signals. They both have
white 2 conductor wire with a black line on one of the conductors.
On Monday, June 25, 2012 at 5:37:06 PM UTC-4, Bob F wrote:light pulse from the LED module. The control unit watches for pulses on the power leads. No pulses means the light path is blocked.
I picked up a couple pairs of these Liftmaster 41A5034 garage door safety sensors, which I thought I might be able to use for other sensing on my homebrew
home control system. Does anyone know what voltage/current the sender needs, and
what connections the 2 wire detector needs and how it signals. They both have
white 2 conductor wire with a black line on one of the conductors.
The way that the sensors work might be this: The transmit module power leads and the sensor power leads are connected in parallel. The transmit module pulses on at a fixed rate. The detector module shorts out the power leads whenever it detects a
With the devices hooked up, an oscilloscope was used to see what was going on. With the light blocked between the transmitter and receiver, the white/black wire is 6VDC above the white wire. When not blocked, a periodic signal is observed, where thewhite/black wire is 6V above the white wire for about 5.5 ms, then falls close to 0V for about 0.5 ms. This suggests that the opener is supplying 6V through a resistor -- the receiver is "pulling" the voltage to (near) 0V briefly and periodically. One
oscilloscope picture The devices were removed from the opener. With a DC voltmeter across the terminals on the opener, the voltage was measured while resistors with gradually decreasing values were put across the terminals. Since the small boxes bothhave lit LED's when operating, the internal equivalent resistance can't much more than about 1k for a 6V source, so that was the starting value for the external resistors. A significant drop in voltage (though less than by 1/2) was noted for a couple
A 6V power supply was wired through a 150 ohm resistor to the two boxes. Plus to the white/black wire, 0V (gnd) to the white wire. The signal was observed to be virtually identical to what was observed from the opener, except the maximum was closer to5V rather than 6V. It might be that a smaller resistor is expected or that the circuit is not linear (hence, Thevenin's theorem is not applicable). But it works, anyway.
photo of circuit To make a completed electric eye for use without the opener, a small circuit board was used which included a 6V regulator (7806) and a 555 (low-power) wired as a "missing pulse detector." The circuitry for the latter can be found onthe 555 data sheet, and is easily found with an internet search. It has been copied and recopied by many. Referring to that diagram, I used a 2N3906 PNP transistor, and a 0.1 uF capacitor and a 75k resistor for the timing. The power was supplied through
Pin 3 of the 555 goes low when the light beam is broken, and is high otherwise. So far it is just wired to light an LED. I am not sure what I might use the electric eye for as of yet. Perhaps something to do with trick or treaters?
Note that in the process of testing, I tried various power supply voltages. The frequency of the pulses does depend on the voltage. A 5V source still seems to work, though the frequency is not as steady
With the devices hooked up, an oscilloscope was used to see what was going on. With the light blocked between the transmitter and receiver, the white/black wire is 6VDC above the white wire. When not blocked, a periodic signal is observed, where thewhite/black wire is 6V above the white wire for about 5.5 ms, then falls close to 0V for about 0.5 ms. This suggests that the opener is supplying 6V through a resistor -- the receiver is "pulling" the voltage to (near) 0V briefly and periodically. One
oscilloscope picture The devices were removed from the opener. With a DC voltmeter across the terminals on the opener, the voltage was measured while resistors with gradually decreasing values were put across the terminals. Since the small boxes bothhave lit LED's when operating, the internal equivalent resistance can't much more than about 1k for a 6V source, so that was the starting value for the external resistors. A significant drop in voltage (though less than by 1/2) was noted for a couple
A 6V power supply was wired through a 150 ohm resistor to the two boxes. Plus to the white/black wire, 0V (gnd) to the white wire. The signal was observed to be virtually identical to what was observed from the opener, except the maximum was closer to5V rather than 6V. It might be that a smaller resistor is expected or that the circuit is not linear (hence, Thevenin's theorem is not applicable). But it works, anyway.
photo of circuit To make a completed electric eye for use without the opener, a small circuit board was used which included a 6V regulator (7806) and a 555 (low-power) wired as a "missing pulse detector." The circuitry for the latter can be found onthe 555 data sheet, and is easily found with an internet search. It has been copied and recopied by many. Referring to that diagram, I used a 2N3906 PNP transistor, and a 0.1 uF capacitor and a 75k resistor for the timing. The power was supplied through
Pin 3 of the 555 goes low when the light beam is broken, and is high otherwise. So far it is just wired to light an LED. I am not sure what I might use the electric eye for as of yet. Perhaps something to do with trick or treaters?
Note that in the process of testing, I tried various power supply voltages. The frequency of the pulses does depend on the voltage. A 5V source still seems to work, though the frequency is not as steady
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