Did I just kill my Uno?

I was working on a project before I left for work and powered it up and did not have one resistor (a pressure sensor) connected to a leg of a voltage divider. Now I’m sitting at work and realized that I sent 9V to an analog pin!!! It was turned on and off for few short periods of time (30 seconds or less) and the program in the Arduino was not looking for a signal at that pin. I’m worried that when I get home, I’ll find that I cooked the A0 pin on the uno.

Three quick questions:

I know that it does not take more than a split second of high voltage on the IC to ruin it, but what are the chances that it will be ok? If I did not cook that input, will it be reliable or should I just use a new pin? If I DID cook it, will it affect all of the ADC pins?

Right now I’m SO mad at myself for forgetting to plug that sensor in and can not believe that I totally zoned out on the fact that 9V was being fed to an analog pin.

:blush:

The Arduino inputs have some protection. If the 9V (why not 5v?) was connected through a resistor you should be fine. Even if not there is a good chance it will survive. Good luck.

A new ATmega328 with the Arduino bootloader should cost well under $10.

The voltage divider was as follows:

9v — 250 ---- Vout ---- 250(pressure sensor) — Grnd

So the 9v had a 250ohm resistor in line prior to the analog pin.

I used 9v to get a larger range on the ADC, however, I’m sure I could have used a lower voltage.

If the arduino was not reading that analog pin, is the circuit still complete?

RobDrizzle: The voltage divider was as follows:

9v --- 250 ---- Vout ---- 250(pressure sensor) --- Grnd

So the 9v had a 250ohm resistor in line prior to the analog pin.

I used 9v to get a larger range on the ADC, however, I'm sure I could have used a lower voltage.

If the arduino was not reading that analog pin, is the circuit still complete?

That appears to be a rather strange way to interface a pressure sensor. Do you have a link for the sensor that we could look over?

Lefty

It's a car oil pressure sensor ;)

FYI Autometer Model 2242, 100 PSI. It's resistance is 250 ohm @ 100 psi -> 30 ohm @ 0 PSI.

For those who are reading... Amazingly, the pin is still functioning correctly!!!

RobDrizzle: For those who are reading... Amazingly, the pin is still functioning correctly!!!

The series 250 ohm resistor probably limited the current flow going through the internal positive clamping diode. However maybe your just lucky. :D

Lefty

RobDrizzle: I used 9v to get a larger range on the ADC, however, I'm sure I could have used a lower voltage.

Another way to get a full range out of a voltage divider is to use a 3.3v analog reference instead of the default 5v. Then you can use the 5v supply for the high end of the divider.