The SAME screw terminal that supplies the power to the sensor is also
supplying the power to the IR beam transmitter. That means that there is
always current flowing, because the transmitter must keep sending the
beam. For you theory to be correct, the circuit would have to be
differentiating between two different amounts of current. That's possible,
I suppose, but I don't know if that's what it really does.
The pushbutton control on my wall also does something similar. It has a
button to open/close the door, and another to just turn on the
light. Again just two wires. Somehow, it knows which button is pressed.
-Steve
At 07:26 PM 3/23/03 -0500, Donald H Locker wrote:
>No guarantee, but if I were designing the circuitry, the lead that
>carries power would also serve as the signal -- with nothing
>interrupting the beam, current flows; when something interrupts the
>beam, the current stops and my control logic watches for current
>flow. This also either stops the motor or raises the door if the
>wires to the sensors fail.
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