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[on:]

Board: Arduino Uno

I suspect the ADC on my Arduino has fried. When I call analogRead() on any of the pins (tried 3,4,5) and print the value to the serial port I read a value that starts at 300 and drops until it stabilizes around 250, similar to what you see for a floating pin. Here is the pertinent part of the code I am using for testing.

Code:

void loop()
{
  val = analogRead(5); 
  Serial.println(val);
}

The output on the serial monitor looks something like:

300
295
290
284
...
256
255
256
255

I have the wiper of a pot connected to pin 5 and have used a volt meter to make sure the pot is not faulty.

At this point I'm assuming the ADC is friend and I need a new chip. Is there anything else worth looking into before I place the order?

Thanks.

- Matt

[Reply #1 on:]

What is the value of the pot?

[Reply #2 on:]

What does the volt meter read when you are making your measurements?

What is returned when you connect the analog input directly to 5v or GND?

[Reply #3 on:]

Well before tossing the chip, disconnect your wiring to analog pin 5 and wire it to ground and see what value you get back, should be 0 counts. Then wire the pin to +5vdc, it should then read 1023 counts. If that works post your wiring drawing and include component values and we shall have a look.

Lefty

[Reply #4 on:]

The output on the serial monitor looks something like:

300
295
290
284
...
256
255
256
255

I have the wiper of a pot connected to pin 5 and have used a volt meter to make sure the pot is not faulty.

That's entirely normal if you are using a high-value pot, e.g. 1Mohm. You should not see that effect if the pot is ~10Kohm or lower.

[Reply #5 on:]

I'm quite embarrassed to admit it, but this turned out to be a case of "tinkering late at night after a long day in the office" and can be chalked up to a simple oversight. I managed to plug into D5 instead of A5, arg......

Thanks to all who replied, and I sincerely apologize for wasting space on the board. As penance I will try to drop by more often to give input on any questions I can help with.

- Matt

[Reply #6 on:]

I'm quite embarrassed to admit it, but this turned out to be a case of "tinkering late at night after a long day in the office" and can be chalked up to a simple oversight. I managed to plug into D5 instead of A5, arg......

Thanks to all who replied, and I sincerely apologize for wasting space on the board. As penance I will try to drop by more often to give input on any questions I can help with.

- Matt

No problem, brain farts are allowed and happen to all of us from time to time.  

In the Air Force we would call such problem sources as "A short between the headsets"