I had my sketch uplaoded and everything was working fine when I tried connecting one of the input pins(pre-configured as digital INPUT) to 12V, just to see if this was being read as a HIGH as well. It seems to have done something and the board stopped working. Moreover, all pins seem to be stuck at HIGH!

So far Ive tried the following:

  • reset button: doesnt help
  • re-upload: doesn't work - it says not in sync

Physically nothing seems to be burnt/blown. What am I missing? Have I fried my board? I hope not. PS: It was connected to a 12V external power source

Any thoughts?

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    If you have an Uno with the ATMega328 in a socket, you could just replace the chip with a new one (with bootloader pre-programmed). If it's the SMD version, you're out of luck (unless you have a friend that does SMD soldering). – Gerben Dec 18 '14 at 16:02
  • @Gerben :That seems like a good option, do you know where I can get a bootloader programmed ATMega328? – Ameya Dec 18 '14 at 19:05
  • @Gerben : Do you know where I can get a bootloader programmed ATMega 328? I think i can replace it, luckily my board came with an IC socket. – Ameya Dec 18 '14 at 19:07
  • I don't know where you live. But try stores that also sell regular arduino's. E.g. Sparkfun sells them. – Gerben Dec 19 '14 at 15:29
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    @Gerben Thanks Gerben. I found some for a good price on Amazon. Thank God for Amazon! :-) – Ameya Dec 20 '14 at 0:02

Unfortunately, the arduino's input pins are not tolerant of 12 volts, You have likely caused permanent damage to the chip =(. There is a regulator that makes it capable of being powered by 12 volts, but the input pins are different.

If you look at table 30-1 on the datasheet for the Uno's controller here you can see the input characteristics. The arduino is powered at 5v, so the max digital input voltage is 5.5v

  • Thats good to know. I assumed they could take anything up to 20V!(as rather silly assumption. Looks like I will have to use a voltage divider to sample the input voltage and get it under 5V for my use. Thanks Brett! – Ameya Dec 18 '14 at 19:09

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