My project requirement is to make an analog current input to ADC of microcontroller. Analog input current has 4-20mA specification.
Since I don't have particular industrial sensor with 4-20mA specification, I realised this 15mA current source circuit for testing with my ADC interfacing.
Instead on getting same voltage on either side of the circuit, the ADC input always reads zero. Please look into the issue.
I made a circuit arrangement for analog current input test input for 3.7V compatible ARM microcontroller (figures used for symbolic purpose). There are two things happened here:
- Since 15mA current is passing through 185 Ω, I am getting 2.774V (practical value) across the resistor and MCU should interprete the same voltage in ADC values. I was not getting any ADC values, Is my circuit arrangement correct?
PS: I already smoked the microcontroller while connecting both analog and digital ground together in order to provide reference voltage to microcontroller.
Best Answer
A- Your microcontroller and analog circuitry do not share a common ground, so A/D readings don't have much meaning.
B- the microcontroller measures voltage with respect to some reference, not "across a resistor", unless you provide that reference at one end of the resistor.
C- your microcontroller smoked because when you hooked your grounds together, the A/D input saw 12V.