"Dirty" switch - more voltage? power? amps?

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Sat 18 Aug 2007 09:43
"Dirty" switch - more voltage? power? amps? - mfarrow
Hi

I have a bespoke system on my car which by-passes the manufacturer's headlight switch in order to resolve a full beam switching problem.

The problem I have is that after implementing the system I find the full beam switch becomes dirty very quickly and will not operate on first attempt. The switch is wired up at 5v to a high impedence microcontroller input with a 10k resistor to ground.

My question is what do I need to increase to resolve this problem? Do I increase voltage (i.e. back to 12v), current (i.e. to that it would have seen from a relay coil), or power (i.e. current change taking into account the 5v not 12v)?

Any suggestions welcome.

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Mike Farrow
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Sat 18 Aug 2007 10:25
"Dirty" switch - more voltage? power? amps? - 659FBE
Mike, I'm assuming that the car maker's switch is controlling your microcontroller using a 5V supply with a 10k pull down resistor so the switch current is 0.5 mA.

Two things:

Don't control safety essential lights with a system containing so many elements and in your case, software. You are asking to be plunged into darkness at any time.

You are passing a contact "wetting" current of only 0.5 mA through a car dipswitch which is designed to handle (on cars without relays) several amperes. Car manufacturers are not charitable organisations and don't fit precious metal contacts - they rely on a good dose of current shifting the oxide build-up on the silver (if you're lucky) or brass (if of American origin) contacts. Your circuit will not shift the oxide deposits on the contacts.

For safety's sake, put it all back to OE spec (I'd hate to see an insurance investigation on your present setup) and buy a new dipswitch if you need one - although I suspect normal operating current will condition the contacts and restore normal operation.

659.
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