Hello,
What is the minimum voltage that can be inputted onto one of the Spark Core pins?
I know some are 3.3V tolerant and others are 5V tolerant. But for example can any pin intake 2mV as an input and accurately read 2mV? Or is this too low of a voltage for the Spark Core to handle?
Cheers,
UST
@UST, if you are referring to the analog inputs, the STM32 ADC covers 12bits (4095 count) over 3.3V or approximately 1 mV per bit (805 uV to be exact). At this level, noise becomes a big issue. You may be better served if you pre-amplify the signal first with a good low-noise op-amp with a gain suitable to the range of voltages you want to measure. This will serve as both an isolator and will decouple the impedance of your source from the input impedance of the analog input. Perhaps if you can explain your application, we can guide you better. 
Thanks for the speedy reply @peekay123 !
I’m interested in using a linear hall-effect sensor, the output is in the mV/G range! I would like to have the sensor’s output on one of the Core’s interrupt pins. I want the Core to count every time the poles of my magnets change from North-South, or South-North, but my magnets are weak which is why I’m turning to a linear sensor and not a latch 
So if amplification is necessary then I shall do that!
@UST, in your case noise may be the worst enemy. Since you want to detect a mV range voltage and trigger an interrupt with it, you will need to amplify it considerably (gain > 1000) so noise will be amplified as well. You will just need to follow careful design and make sure the voltage to the analog pin NEVER exceeds 3.3V or else you risk damaging your Core. You may also want to consider using a comparator instead or configure the op-amp as a comparator to produce a cleaner digital output.
Alright I’ll give this a try when I get my hands on the sensor! Thanks for the insight 