I know very little about electronics, but I am trying to make what seems like a simple voltage monitor using an ADC board and the RPi.
I want to monitor the voltage of a 20Ah AGM 12V battery (not to scale in the diagrams).
I am using this board which uses I2C and a couple of ADC chips:
ADC Board Product Page
ADC Board Schematic PDF
The board works fine, I have tested it with a simple 3-pole thermistor and it worked as expected when the thermistor was powered from the ADC board's 5V and GND pins.
However, now I need to actually try and do the voltage monitoring of the separate 12V battery and I am a bit clueless in the proper way to do that.
What I have done is create a simple voltage divider circuit with 2 resistors, R1 100K Ohm and R2 33K Ohm which divides the 12V by about 4.
This simple circuit works fine, my digital multi meter shows that if the battery is at 12V the Vout of the circuit is 3V when measured on the breadboard. So far so good.
It is when I try and feed that 3V from the breadboard to the ADC board attached to the RPi I run into trouble and have no idea the right way to do it.
The ADC board is connected with a stacking header to P1 on the RPi and is powered via the RPi 5V pin from a separate power supply that is powering the RPi.
If I just take the Vout from my voltage dividing circuit and put it into one of the analog pins of the ADC, the ADC reads nothing, no current, 0V.
To get the ADC board to read anything, I connected the GND pin from the ADC board to the GND rail on my breadboard, but if I do that, the voltage the ADC reads in only 1.27V and my DMM also shows 1.27 as the Vout voltage when measured on the breadboard.
What am I doing wrong here? What is the correct way to connect this circuit to my ADC board so the ADC reads the correct 3V from my voltage dividing circuit.
The attached images are exactly as I have my breadboard set up, right down to which holes I have my wires inserted into.
Any help is greatly appreciated.