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Old 30th September 2005, 04:54 PM   #1
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Default Really easy question for the right person...

This should be a really simple question. I'm trying to jerry-rig a setup in my car so I can use my ipod without too much modification. Right now I have an XM-Radio FM Modulator that only turns on when the XM Radio is on. The XM radio draws 6v from it, but I want to be able to turn on the modulator without turning on the XM Radio -- how can I simulate a 6v/(?amps) draw?

Thanks for any ideas!
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Old 30th September 2005, 05:50 PM   #2
anatech is offline anatech  Canada
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Hi wotan2525,
I guess the first question is, how much current do you need to draw?

Be very careful not to short the connections so you don't damage the modulator. You can try using resistors starting from, say 10K down until it turns on. Don't go too low. 620 R should turn it on for sure since the draw would be just under 10mA. Don't start there, draw as little as you need with a safety factor.

-Chris
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Old 30th September 2005, 05:52 PM   #3
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Thanks for the reply... sorry to sound like a complete noob, but should i just place a single resistor between the + and ground? I was thinking I'd put a switch in-line as well -- would it make a difference whether I am switching the ground or the +?

Thanks Again!
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Old 30th September 2005, 06:01 PM   #4
anatech is offline anatech  Canada
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Hi wotan2525,
Yes, a single resistor will do it. Place the switch on the ground side with the resistor as close to the unit as possible. This will reduce the chance of a short causing damage. Worst case, a short will turn the unit on.
-Chris
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Old 30th September 2005, 06:11 PM   #5
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Thanks chris..... sounds easy enough!
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Old 30th September 2005, 06:19 PM   #6
anatech is offline anatech  Canada
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Hi wotan2525,
It is, unless your unit is communicating a digital signal back and forth. But then, it won't turn on.

-Chris
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Old 30th September 2005, 10:49 PM   #7
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Well -- I tried the resistors and could not get it to turn on. My first idea is that maybe when the unit turns on it sends an audio signal that tells the FM mod that it is "turning on" but I'm not sure how likely this is because when I turn the XM on there is a few second delay while it boots up and during that time you can hear the FM mod kick on almost immediately.

Any other ideas for me?

Thanks

Rob
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Old 30th September 2005, 11:22 PM   #8
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Ok... I found a post on an xm board that the guy was working on the same thing but never updated the thread....

Quote:
Just FYI, I tried a 33 ohm resistor and it did not turn on. I didn't hold it in the plug for long, because it was burning my fingers (ouch!) I did hook up my home dock with the XM and it did turn on the modulator. I noticed that it takes about 1-2 seconds for the modulator to turn on...I wasn't able to hold the resistor that long without physical injury. Shocked I'll have to try again with some clip leads and a higher wattage resistor and see what happens.
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Old 1st October 2005, 12:01 AM   #9
anatech is offline anatech  Canada
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Hi wotan2525,
Why not ask an authorized service center about it?

-Chris
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Old 1st October 2005, 01:14 AM   #10
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I Called the xm/delphi people and they just pretty much told me that I didn't need to have that info.

I tried it with a 1ohm/10watt resistor and the unit oscillated between on and off really quickly. It didn't even turn on with a 50ohm/10watt resistor.

I'm really stumped/frustrated.
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