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Old 04-02-2008, 11:14 PM   #1
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low voltage


how does a low voltage circuit, e.g. garage door opener button, receive power and send the command back to the unit over the same two wires?

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Old 04-05-2008, 11:28 AM   #2
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On a two-wire setup where there's only one button, the button is a simple switch. Just like a light switch.

On a two-wire garage door opener control with more than one button, there's always a small steady current flowing through wires to the push-button station. When a button is pressed, it sends a specific pulsed signal (different for each button) back up the wires. The motor part sees this, and does what its told.

Rob

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Old 04-05-2008, 01:19 PM   #3
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Originally Posted by johnpaul1 View Post
how does a low voltage circuit, e.g. garage door opener button, receive power and send the command back to the unit over the same two wires?
There are a couple of ways this can be accomplished. One is what micromind details, different pulse widths can be detected by a circuit in the device being controlled. You could also have different buttons have different resistances. For example, there may be a constant 10 M resistance between the two wires. When you press button 1, it drops to 10 k. When you press button 2 it drops to 50 k. A circuit in the device can tell which button was pressed by the resistance across the two wires.

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Old 04-05-2008, 01:39 PM   #4
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I would think that a simple latching relay would do the same thing...

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Old 04-05-2008, 01:49 PM   #5
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Originally Posted by kencaz View Post
I would think that a simple latching relay would do the same thing...

KC
For more than one function? That would probably require at least 3 wires for two relays.

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