# Interesting problem



## cooldude117 (Jul 29, 2010)

I need a real electronic savvy person's opinion on how to solve my problem. I have installed an Alpine INA-W900 with a back-up camera. The problem is that every time I step on the brakes the deck quickly flashes into back-up camera mode. The reverse sense wire is attached to the positive line of the back-up light. I've done a little bit of searching and it seems like I'm the only one having this problem. I did a little more searching and testing and I think I've figured out the root of my problem, I just need a solution. It's installed in a 2005 Dodge Ram, and there's this handy system that lights up a dummy light on the dashboard if any of your exterior bulbs have burnt out. In order to do this it sends a pulse of very low voltage (a couple hundred mV, enough to test it, but not light the bulb) just before the light turns on (the whole rear harness gets checked whenever any of the bulbs turn on, therefore every time I step on the brakes the back-up bulbs gets checked too) and the computer reads the resultant current to find out if the resistance is proper in the bulb to see if it's still there (I don't know the exact specifics of the test, just that at the bulb it pulses the low voltage). No one else is having this problem because their decks ignore the low voltage and will only trip into backup mode when it sees ~12V. My Alpine deck is much more sensitive and responds to this low voltage signal and trips the backup mode every time the bulb gets checked. The line I've tapped into gets the ~12V every time I'm in reverse, so it is the wire I need to be tapped into, I just need something to block the low voltage pulse from reaching the deck. I've thought of a couple of ideas, I just need someone with more electronics theroy to confirm if what I've read will work in the way I want it to. 
First Idea: Install a relay in my reverse sense line that requires more than 1V to trip the coil.
Second Idea: If what I've read is correct, this is my preferred solution because it's solid state. Install a Zener Diode "backwards" in the reverse sense wire with a breakdown voltage sufficient to block the test voltage, but allow the actual signal I'm after.

I'm almost positive the first option I thought of will work, however I'd really prefer something that's solid state. If my second idea will work, or you know another solution that will work please let me know. 

Thanks


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## Austin (Mar 12, 2009)

I am pretty confident a relay would work, i think they need well up near 12 volts to trigger them. I know a few hundredths of a volt wouldn't trip them but i have not tested this.


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## cooldude117 (Jul 29, 2010)

I tested a relay I had laying around with a 1.5V AA cell and it wasn't enough to click the coil over, so I'm confident that will work, I was just hoping for a more solid state solution if one existed.


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## Volenti (Feb 17, 2010)

Haven't done much with zener diodes recently but it should work in theory, not like it'll cost much to try anyway.


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## mike_d_us_amp (Feb 23, 2007)

Would triggering a relay off of the back up light circuit load down the computer side, because of the resistance across the coil? These car computers are so sensitive. I think the zener diode would work out.


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## Austin (Mar 12, 2009)

mike_d_us_amp said:


> Would triggering a relay off of the back up light circuit load down the computer side, because of the resistance across the coil? These car computers are so sensitive. I think the zener diode would work out.


Oh i didn't think of that...Good point.


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## MidnightG35X (Feb 5, 2009)

Why not try just a regular diode in series? If the pulsed signal is really only a couple hundred mV, then a regular 1N4004 diode should work fine. They have ~1V drop.


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## sqshoestring (Jun 19, 2007)

You could make it like a muting circuit in an amp with a resistor that fills a cap which turns on a transistor (or relay), make it so the pulse does not fill it and it will not turn on. Basically a timer. Or the right diode should work too if the pulse is not 12v. Even a cap and resistor might work.


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