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# simplest way to invert + to -?

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#### Terje Høegh Sæverud

##### New Member
Hi all. I am putting an accessory in my car that is a mirror with lights that are to turn on with my dome lights. So I took my dome light wire for a signal, but it is + and the mirror lights turn on with -, so the mirror lights were working opposite the dome light.

What is the most simple way to change the + to - so the mirror lights will work the correct way? (but not with a relay because that is too loud in the cabin)

I was thinking to use a logic IC NOT gate, or a transistor inverter NOT gate. Which is more simple for a car environment?

My mirror lights takes .43 amps. Is there a logic IC made that will work for me?

Thanks you all

The dome lights are normally connected to the + battery voltage and turn on when the door (or another switch) grounds the - side of the light.

Can't you connect the mirror light the same way with the battery to the + lead and the - lead to the door switches?

The mirror has to have two lines on it some place. Just connect it so the the right wire is grounded and the other to feed it. Or reverse of that if that how the vehicle is wired up.

The car is new, uses CANBUS and the only way I can take trigger from the dome light is via the +. Likewise the mirror is multifunction, temp, comp, autodim, independent light control, dome light, so the only way I can go into it for dome light function is with the -.

A transistor with the appropriate base resistor will work.
I'm a little confused by:
the only way I can take trigger from the dome light is via the +.
Do you mean that the switch for the dome light is in the +12V lead or in the chassis ground side? Knowing that will determine whether you use an NPN or PNP transistor.

What kind car is this you can get the wiring of most on the net.
The car is new, uses CANBUS and the only way I can take trigger from the dome light is via the +. Likewise the mirror is multifunction, temp, comp, autodim, independent light control, dome light, so the only way I can go into it for dome light function is with the -.
I would like to see this sounds cool

The mirror is complex, multifunction and has seperate controls for the same lights I want triggered, so the only way I can do it is by triggering through the "-".

Should this gate driver work? FAN3223TMXCT, datesheet HERE.

Or this MC34167T? datasheet HERE.

^Could I hook up either of those directly without other parts?

If I did a transistor and resistors, a TIP31 NPN Transistor, and my math tell me 10k ohm 5 Watt Base resistor and 30 ohm 5 Watt Collector resistor? Trigger into Base, output to Collector. Do I not need Collector resistor?

Thanks
Terje

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