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I'm building what I thought was a simple Arduino Nano project... right up until it caught fire!

I am a long-time reader of stack exchange and I always find the answers to my questions somewhere on Google, but this seems to be a bit of a head scratcher.

The project is a 4 pin 7 segment LED screen with a timer that counts when Analog pin 0 receives a voltage signal of ~2.5-5v.

Testing the project worked as expected, but when I soldered everything together, I was getting static or white noise from the Analog pin with no voltage being supplied.

I figured I needed a Pull-Down resistor to keep the Analog pin grounded until it received a voltage signal to get rid of any interference.

I connected a 220ohm resistor DIRECTLY from GND and DIRECTLY to Analog Pin 0 and connected the voltage signal wire to Pin 0 as well.

When I actually tested the hardware while connected to the car battery, that's when it shorted out and caused a mini fire.

I was able to read the voltage with my multimeter before the chip burnt out, I was reading ~15.5v total. I'm guessing it's the car battery plus the input voltage on Pin 0.

I only do clean and precise soldering, so there were no unaccounted for connections.

I'm unsure if the issue was too many volts running through the Nano altogether or because I don't really understand how the Pull-Down resistor works and messed that up.

Please help me understand what the issue is and what I can do for a solution.

Thank you.

Schematic

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  • Arduino Nano accept up to 12V. On which pin have you connected the battery? What voltage are you measuring now on the battery? Have you connected the grounds of the car battery with the ground of the input signal?
    – Nino
    Jul 27 at 13:59
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    Could you manage to draw a schematic? That will make things a lot clearer probably! Did you connect the battery minus to the Arduino Vcc (as that is the only way the voltages could “add up” as you said)? And how did you come up with a value of 220 Ohms (which is quite a low value for a pull down resistor)?
    – StarCat
    Jul 27 at 14:04
  • I've added a schematic. For some reason one line of text didn't save. The pink wire is CLK, but I don't think that's relevant to my original question. The 220ohm was a suggestion someone made to me, but I have no idea. I haven't dealt with resistors before.
    – Eli
    Jul 27 at 14:46
  • What is that external 5V signal? Did you connect it with just one wire? And what exactly did burn? Something on the Arduino? If yes, how much current does the LED display draw? You might overload the voltage regulator. And a pulldown resistor as small as 1 to 4kOhm is already considered very strong. Normally you would use something like 10kOhm
    – chrisl
    Jul 27 at 15:57
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    the +5 V and GND on the device can easily be +12 V and +7 V when referenced to the vehicle battery negative
    – jsotola
    Jul 27 at 17:05
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You violated the voltage input specification of A0 by a lot. What happened is what I would expect. The input protection diode on A0 conducted the battery voltage (- the protection diode drop) into the VCC of the Nano, this overvoltage fried just about all semiconductors and possibly several of the passive components on the board. It sounds like they do what they do when abused and they let the smoke out destroying the Nano and possible several other components. Hopefully this explains what happened. If you had connected the resistor between A0 and the battery it might have survived.

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Input power

Car power systems operate between 13 and 15 volts when the car is running. Might be too high for the voltage regulator on the Nano. Mine is a AMS1117 which goes up to 15v. Sounds like that's what fried based on your description. Some fail closed circuit, so may have exposed the ATMega to 14v. There's some alternative voltage regulators with the same footprint that will go up to 20v or more input, look for one of those. SOT-223 footprint.

Button

The Nano/ATMegs has internal pullups. I'd use those; connect the one side of your button to ground rather than 5v, and the other to the Nano digital input. In your code, activate on LOW rather than HIGH. Then you can skip your external pullup.

Pullups

220 ohms is a very strong pulldown for the 5v signal. It will be seeing .11 watts of power dissipation. Use something higher like 10K or 100K. Put a 1K resistor on the 5v signal to limit it's current. You're Arduino is only sensing the voltage, so with a 10K to GND and 1K from 5v signal, the resistor divider will signal 4.5v, plenty for your Nano to detect "HIGH".

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  • What do you do when you get a double battery jump. How about load dump?
    – Gil
    Jul 29 at 2:45

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