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photo cells

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rbig

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In some ways, I understand photocells. You break the beam of light between them, it triggers something.

My question is the photo cells themselves. Here, I'm talking about garage door kinds. Is each a small transmitter and receiver?

Both seem to be powered up by the garage door opener. If one is a transmitter and one a receiver it would seem that it would require an expanded way of powering them.

Right now, there are two terminals. This sort of tells me each is a transmitter and receiver. Just curious.
 
Those are not really photocells, A photocell is a component that changes it's resistance according to the intensity of the light shining on it. What you have is called a photo-eye or photodetector. There are several names that are used for them. The ones I have seen on garage doors that use two wires one is a transmitter and the other is a receiver.
 
Maybe post a picture of the units.. The LDR/photo cell is a light variable (detecting) resistor, as stated.

Does your system have wires on each end (side) of tiyr garage? Some units are TX/RX and use a reflective object to send the beam back.
 
Typically the transmitter would be an LED (visible or IR) and the receiver with be a photo-transistor. To minimize interference the LED can be rapidly turned on and off (modulated) to generated an AC signal at the receiver. The receiver than amplifies the AC and blocks any DC to avoid interference from ambient lights. The AC signal can be send back on the same two wires that provide DC power to the receiver.
 
More good info: It turns out that there are two connections on the ceiling unit. They are marked for the cells.

It turns out my photo cells look the same. They're not. One is a receptor, the other is a transmitter. Both have small lites on them, and they should shine brightly, as long as the units "see" each other. So, we have one receptor, with two leads. We have one transmitter with two leads. These may be infrared--not sure.

I'm wondering which leads on the ceiling unit go to the receptor and transmitter?

I guess this thing works by the light beam interruption breaks a circuit, which causes the door to not come on down.

Still not sure how it breaks the circuit. Maybe with ac as crutshow explains.
 
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