For context: I'm working on a whose goal is to sense the environment. This process is done using an Arduino Uno and an RPi. The easiest way that I found to perform communication between both boards is by uploading Standard Firmata and reading the code from RPi using Serial communication. I'm using pyfirmata to write the code in Python on the RPI side. Also, the Arduino is powered by the RPi using the USB port.
My problem was: The ADC component in the Arduino uses as the analog reference the 5V provided by the USB. When I tested the integration, I was using my laptop. So, the computer was providing 5V to the Arduino. So far so good. When I integrated the Arduino board to the RPi, I got some problems related to the precision of the sensor. I figured out that the RPi was only giving 4.75 V to the Arduino Board. This was messing with my readings since the ADC was using 4.75V while my code had 5V to compute things. After adjusting the code, everything proceeded as planned. Both 4.75 V and 5 V were hardcoded in my code.
So, these are my questions:
- Is there a way to read the Vcc using pyfirmata to figure out the correct voltage without having this hardcoded?
- Is there a way to modify the analog reference to use the INTERNAL reference of 1.1V?
About the analog reference, I found this: https://github.com/firmata/arduino/issues/39 . So, pyfirmata implements send_sysex method, I just have to execute these steps, but I still don't know how.