I have connected an Arduino Pro-Mini 3.3V 8MHz to an ESP8266 via I2C.
The Arduino is in charge of collecting data from a thermistor (analog temperature) (T2) and a SI7021 (digital temperature) (T1).
The ESP8266 is in charge of sending the data received from the Arduino to an endpoint.
Here is my repo: https://github.com/ClemRz/Solar-Water-Heater-Monitor. In the res folder you will find a picture of the circuit.
The issue I am having is that as long as I leave the FTDI RS232 programmer connected to either the Arduino or the ESP I'm having a smooth response from the thermistor but as soon as I disconnect it, the response get some noise. What is happening?
Here is a graph where we can see 3 phases:
- Programmer disconnected: some noise can be seen
- Programmer connected: smooth noiseless curve
- Programmer disconnected again: noisy
If I remove Rx and Tx and I leave GND connected to the FTDI I also observe that the reading is smooth and noiseless.
EDIT: I switched the wall adapter with a better quality one and it fixed the noise issue.