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Utilizing 3rd channel for own uses

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Old 09-06-2004, 09:18 AM
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creyc
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Default Utilizing 3rd channel for own uses

I have a JR XS3 radio and RS300 receiver with three channels in my electric TC3. I'm wiring up a lighting system for the car and would like to use the 3rd channel of my servo to turn the lights on or off. I'll use a transistor to actually do the switching but I'm not sure how to turn a signal from the three pins (black, red, yellow) into something I can use to change a voltage. If anyone has a schematic on a circuit that will do this for me it would be a big help.

I'm under the impression I'll need to build a pulse-width-demodulator to decode the pulses sent over the yellow wire. I have an old servo I could pull the electronics out of possibly if that would help. Anyone already created a system to use a particular channel for their own circuits could help me out.
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Old 09-06-2004, 01:49 PM
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Phil Cole
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Default RE: Utilizing 3rd channel for own uses

This page has something you could adapt:

http://www.cliftech.com/

Or else, you could just wire the LEDs in place of the servo motor. Put in a series diode so you don't reverse bias the LEDs.

Substitute some fixed value resistors for the servo position feedback pot so the servo thinks it's in the middle.
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Old 09-06-2004, 02:06 PM
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Default RE: Utilizing 3rd channel for own uses

A carefully selected resistor and capacitor would allow you to switch LED's on and off directly from the signal line, at least via a transistor. You'd have to sit down and work out the math or just tweak it, but a far left servo signal pulse is on for 1 ms 50 times a second, and a full right servo signal is on for 2ms 50 times a second. When that's filtered through a resistor and capacitor it translates to a steady state voltage (roughly) The key is getting the resistor right so that the voltage drops bellow the LED's threshold voltage at the far left position. Using a multi-turn low ohm potentiometer should give you pretty fine control. The capacitor would have to be matched to the transitor you used to switch the LED's as some use more current so would require higher capacitor to cause it to switch. A logic level mosfet would be ideal as you could use a minimally sized capacitor for it. The benefit of doing it this way is if you bias your resistor and capacitor just right you'll have a decent level of brightness control. You could build the whole thing on perf board, or wire it up dead bug style after you test it on a breadboard. Really shouldn't be too hard.
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Old 09-06-2004, 09:43 PM
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Default RE: Utilizing 3rd channel for own uses

you could also use a servo to push a switch to turn on the lights
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Old 09-07-2004, 07:26 AM
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Default RE: Utilizing 3rd channel for own uses

Check out Precision Micro Electronics: http://www.pme-rc.com/
Down load his catalog and checkout the Low Voltage Accessory switch, designed to do exactly what you want.
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