-1

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: https://i.stack.imgur.com/TsnvY.png

  1. Programmer disconnected: some noise can be seen
  2. Programmer connected: smooth noiseless curve
  3. 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.

Solved: I switched the wall adapter to a better quality one and it fixed the noise issue.

Cœur
  • 37,241
  • 25
  • 195
  • 267
ClemRz
  • 126
  • 1
  • 11

3 Answers3

1

I checked your circuit in Fritzing, if you are using a NTC Thermistor, you need to connect on pin to 5V and the other pin to your Analogic Input with a pull-down resistor. Just like this image.

NTC Thermistor to Arduino

I hope this help you to read good analog signals of the thermistor

A5C1D2H2I1M1N2O1R2T1
  • 190,393
  • 28
  • 405
  • 485
Antonio Bretón
  • 11
  • 1
  • Thank you for your comment but I followed the documentation provided here which uses a pull-up resistor: https://learn.adafruit.com/thermistor/using-a-thermistor If that would be an issue how do you explain that I get no noise when connecting FTDI's GND pin? – ClemRz Oct 06 '17 at 03:40
  • You can also use a capacitor connected to the Analog Input and ground. This helps a lot to reduce noise from the 5V rail. This because the 5V rail is sensitive to the noise that can make other components like switches, relays and communication buses. a 0.1uF capacitor may work fine. – Antonio Bretón Oct 06 '17 at 16:57
0

Where do you get the power supply from when you disconnect the FTDI interface?

I've experienced the same issue when I don't wire the grounds properly. Double check all your grounds are wired together (from your main circuit and from the FTDI/USB). Remember ground is a voltage reference that must remain consistent throughout your circuit.

javorosas
  • 759
  • 1
  • 12
  • 22
  • Thanks. The power supply comes from a wall adapter that I regulate with a LM1117-3.3. All components share the same GND. – ClemRz Oct 04 '17 at 23:23
0

Switch the wall adapter with a better quality one and it will fix the noise issue.

ClemRz
  • 126
  • 1
  • 11