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I am working on a project with Raspberry Pi with display, ESP32 with a couple of sensors and an output relay. The basic circuit diagram is shown in the figure below.

Fig1: Circuit Diagram

Now coming straight to the problem. ESP reads the sensors and sends the data to the RPI. it displays the sensor reading in the display live. the sensors consist of a pulse meter based flow sensors and a couple of analog sensors.those part are working fine. Now the esp has some rule engine running inside it, by which it turns on and off a motor. the Motor is a half HP induction diaphram pump.it starts ok. but when the esp shuts it down the display of my raspberry pi turns off and come back on in 2 seconds. It is not turning off the Pi or the esp32, but just gets the display off and on. I tried out various work arounds I can just get to know, like adding a EMI filter as shown in the figure. I am driving the relay via a optocoupler to isolate it from the main circuit. Then I connected my DSO to the 5V SMPS power supply. and found that there is a noise getting injected to the 5V Rail when the motor is turned off. Suprisingly it doesnt happen when the motor is turned on. Figure below will be a pic of the noise i saw across my 5v supply.

DSO Image

I am guessing that noise is causing the problem.

How to prevent this noise from affecting my display? I am sure it might be affecting my raspberry pi too.

EDIT: The EMI filter I am using is shown below and data sheet of the filter is here

EMI Filter

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  • \$\begingroup\$ Please add ground/earth connections to your sketch and properly link the data sheet for the EMI filter and LCD. \$\endgroup\$ Commented Jan 27 at 18:05
  • \$\begingroup\$ @Andyaka added the EMI Filter Spec as edit.. also all the grounds are connecter in commen to the 5V supply -ve terminal. AC Line earth is connected to the motor and there is a earth terminal in EMI Filter. \$\endgroup\$ Commented Jan 27 at 18:41
  • \$\begingroup\$ What are you seeing at the input to your SMPS? Is the voltage surging out of the SMPS max input voltage spec? \$\endgroup\$ Commented Sep 8 at 15:45

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How far is your display from the motor? How far is the wiring?

Your disturbances could be radiated, expecially if display is touchscreen. Try to use shielded cables or ferrite rings along them to see if it gets better.

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  • \$\begingroup\$ Thankyou for your response. The display is around 2 meters away from the motor. but both are placed inside a metal enclosure. The enclosure is earthed along with the motor. \$\endgroup\$ Commented Jan 28 at 1:53
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    \$\begingroup\$ If you fixed your boards with metal screws to the enclosure you probably have the GND pole of your 5V PSU shorted with earth, so every spike you're shunting to earth is transmitted to GND of your display. Try to take out the earth connection from the enclosure to see if it improves, if it works you'll have to keep "motor earth" and "display earth" separated. \$\endgroup\$ Commented Jan 28 at 15:53

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