hey
am trying to sample an analog input with an Uno but having problems.
basically A0 is drawing ridiculous amounts of current, and I don't know why. all the other analog inputs are fine, its just A0.
what could cause this?
I have a 5V zener on the output to stop it going over-voltage, but I did notice it spiking to 10v when i turn the power supply to my circuit on (which was weird). could transient voltage spikes cause it to do this?
thanks
t
What do you have connected to A0?
What do you consider to be "ridiculous amounts of current"? (e.g. how much?)
at the moment nothing, because I don't want to make it any more broken.
an example is in order to test whether it was working as an AIN, 10k potentiometer across 5V/GND and brush to the pin. Any of the other analog input pins I had a value proportional to how far it was turned but A0 got 5V unless it was right at the one end. basically A0 is shorted to 5V...
found this when googling 10 Ways to Destroy an Arduino — Rugged CircuitsRugged Industrial Arduino Microcontrollers, I assumed the 5.6V zener would be fine but if the internal protection diode turns on at 5.5V that would explain why it is now broken and probably why it is shorted to 5V (burned right through diode)
maybe I should go fix that...
OK 
as James asked
(e.g. how much?)
How are you measuring this ,
What do you have connected to A0?
How did you know it was "drawing" to much currect? and what Voltage are you applying?
well i first tried to test using a voltage from a power supply, and at 0.3v or something it was drawing like 400mA at which point i thought it was a good idea to turn it off
the potentiometer was not working as a voltage divider because all of the voltage was between GND and the input no matter where the brush was, which would happen when all the current was flowing through that half of the divider (i.e. brush shorted to 5V). The point at which the voltage on the pin stopped being 5V was right at the end of the pot, meaning only when the resistance between gnd and the pin was tiny so a large amount of current was flowing would it drop (small resistance through exploded ESD diode)
let me figure this out ,are you trying to put/incert Voltage from a external power supply into a input on the arduino, to measure the supply or something ?
i am making an IR ranging unit for a uni project.
arduino provides PWM signal to control the LED pulsing, and samples the signal coming back from the receiver.
the analog input did not seem to be working correctly, so i attempted to test it by supplying voltages from a power supply and potentiometer to see if it gave the right values.
the power supply was putting out half an amp at almost zero voltage so i decided that was not a good idea to continue, tried the pot instead and that did not work because the input drew too much current so it did not operate as a voltage divider
pretty sure the problem is that i have killed that input, have since taped over it and am now using a different one which seems to work fine
Umm im pretty sure putting the half an amp into the analog pin is probably what killed it. In the future for testing pins, try going from 5v to 1 leg of a pot, middle leg to the analog, and last leg to ground. It should make a voltage divider that will let you show the full range, 0-1023 of the analog pin when you turn the pot, and it won't kill the pin, (might damage it if you put the pot @ 0 and have the full current going into the pin though, should probably put identical resistors in series with the gnd and 5v legs. I use ruggeduino now because i know how often i break stuff)
Nikarus:
Umm im pretty sure putting the half an amp into the analog pin is probably what killed it.
You can't "put" current into something. Current flows through the path of least resistance. If a large amount of current seems to be flowing through a high impedance path, that path is no longer high impedance...
the analog input did not seem to be working correctly, so i attempted to test it by supplying voltages from a power supply and potentiometer to see if it gave the right values.
So what voltage did you feed the pot with? The arduino can not stand any more that 5V.
the power supply was putting out half an amp at almost zero voltage
That sounds like the over current limit was kicking in and you were feeding the power supply into a dead short.
Unless you put in greater than 5V it looks like something else killed your input pin.