LCD displaying funny characters when turning on the fan

Other Hardware General Electronics
1

Hi.
I am constructing Greenhouse Automation with Arduino (mega). The project is nearly complete.

Main part of the project is the control unit where I have Arduino, PCB (before breadboard), LCD 16x2, breadboard power supply and 5v relays. This unit is connected to sensors dht11 and 2 soil moisture sensors.
Relays will be controlling 4 circuits:

  1. Soil moisture 1 - 12V DC relay 1 (water).
  2. Soil moisture 2 - 12V DC relay 2 (water).
  3. Temperature - 12V DC linear actuator (windows opening).
  4. Humidity - 230V AC Fan.
    12V will be coming from 12 V DC power supply and 230V from mains.

I tested my control unit several times without connecting it to the greenhouse and actuators. Required relays are activated when needed, depending from temperature, etc.. Generally no issues.
Today I mounted the unit in greenhouse and tested again without connecting the fan, solenoids, or actuator. Still the same - everything works fine.
Now the problem is: I turned on and off the fan (230V) using switch on a fused spur (13A) which is in the same mains radial circuit as sockets where breadboard power supply for my unit is connected. When I turn off this fan, LCD starts to display strange characters, like there was some power interference (I don't know how to name this anomaly). Then, I turn Arduino quickly off. It happens most of times when I turn the fan off but it happened also once when I turned it on.
Does anybody knows what is causing it? Is LCD (16x2) so sensitive to power fluctuations or what? Fan is from Amazon (likely Chinese -38W) but as I say it is still not even connected to relays.
Thanks very much for help.

2

That is electrical interference, either resulting from voltage drops in the AC wiring and and inadequate, poorly filtered power supply, or via radio waves emitted by motors, household wiring and picked up by long, loose wires to sensors, etc.

As a start, make sure that the power supply is adequate, and put the Arduino project in a grounded metal box. You may need to use shielded wire for sensor connections.

For more specific advice post a photo of your project. A hand drawn wiring diagram and links to components would be very helpful.

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What sensors are you using and what are the lead lengths. You are suffering from classic EMI problems. Grounding is very important as is shielding.

1 Like
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And maybe some bypass caps to help smooth out noise and bulk capacitance to supply dips.

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