I'm trying to read the output of an hall effect sensor but the output is always zero. I'm thinking that i might have fried the ADC, what is the max input current for the ADCs?
There is no current limit, but the voltage must be in the range of 0 - 3.3V.
How have you connected the sensor? Most 3-terminal devices connect to 3V3, the ADC pin, and GND. Sensor sensitivity can also be a factor, as the signal could be too low to measure if the field is weak.
the VCC is connected to 3.3V on an external power supply and so is GND, output is connected to A0 and has an output range of 0-0.4V(measured with a multimeter), it works with an 10bit ADC that i was testing with.
0.4V should be around 496 on the 12-bit ADC so that's fine. And you said you had the GND on the Boron connected to the external supply GND, so it should work unless the ADC is damaged.
I'm thinking that the ADC is damaged in some was because when i first ran the code i got about 500 and then i don't think it worked after that
One of the things I frequently do is add a D1213 DLP (data line protection diode). This connects to the ADC input. The external 0-3.3V signal connects via a 100 ohm series resistor.
If the input voltage exceeds 3.3V the diodes and the series resistor will prevent the ADC from damaged. The Zener diode also protects against some ESD damage.
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i believe i know what happened, few month ago i was doing a project and connected 12v power to signal which killed the sensor which is why i got no output from the sensor, but i now think that the ADC die with the sensor and is why it isn't working now
That is likely the cause.
And the protection circuit I posted above can protect against that sort of thing. I had a situation where the sensor was powered at 12V but only output 3.3V, so it should be safe. What I didn't take into account is if the sensor ground came loose, the sensor output would be closer to 10V which would have been fatal to the ADC if not for the protection circuit.
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