I am making a reverse sensing alarm system. I am using a HC-SR04, arduino UNo and a piezo buzzer. The programming was a success however i will like this circuit to be powered when the reverse gear is shifted into place. So I am thinking to power the V in of the UNO with the 10V from the reverse bulb socket receives. However I think the amperage sent to this bulb is too much for my UNO. What should I do ? and Does anyone have any other recommendations to power the UNO in such a scenario?

  • Amps are drawn, not sent. A device will only draw the amps it needs. You might have to add some additional protection, as car voltages are very noisy, with huge spikes, that can easily fry your arduino.
    – Gerben
    Apr 29, 2015 at 19:48

1 Answer 1


Power the Arduino in parallel with the bulb. Take the V+ wire running to the reverse light and the frame ground. The frame ground is any bare metal surface of your car will be grounded, just connect a wire to your frame. Or you can just splice the light bulbs ground wire. When powering the circuit in parallel you do not have to worry about the amperage draw of the light. By a barrel jack connector like this connector from spark fun you can buy these cheaper elsewhere just a 2.1mm barrel jack connector. Connect the positive and negative respectively, and connect the 12v into the Arduino's barrel jack.

As a side note the bulb should be getting 12V not 10V it's not a huge problem, but it is a slight issue that could later be a problem or be caused by an electrical bug. If everything works don't scramble to fix it, but be aware it exists.

  • If you put it in series, the bulb will not light up (too little amps going through both). Just place it in parallel. The arduino will only draw what it needs; a few milliamps.
    – Gerben
    Apr 29, 2015 at 19:45
  • 2
    I made a massive brain fart I just switched series and parallel in the answer. DO NOT WIRE IN SERIES!!
    – Joel
    Apr 29, 2015 at 21:23

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