Relay and LCD

Other Hardware General Electronics
1

Hello All,

Greetings!

I have started a project prototypewhich involves an RFID, RFID controlled door and an LCD. The LCD is used to display the ID from the tags, mostly the name of the user. I use and Arduino Mega, a Relay, a 16x2 LCD Display, a 12V stepper motor for the door, a 12V fan at the door and an MFRC 522 RFID Module.

The problem:

The LCD works very well when the Digital I/O Pins of the Mega are not connected to the relay. But the moment the pins are connected to the relay, the LCD starts misbehaving.

What have I done wrong here? Please help!

Thank you very much

Best wishes and regards
Bob

2

Hi,
Welcome to the forum.

Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?

We need to see how you have connected components to the Aduino.
Do you have transistor or MOSFET drivers for your relays?

Please include how you are powering your project.

Thanks.. Tom.. :slight_smile:

3

Hello Tom,

Thanks for your response and support.

Please find the circuit image attached. I have not used any Transistor or MOSFET Drivers in this project. And as for the powering, the Arduino is connected to the my laptop through USB and the relay is powered by an SMPS giving an Vout of 12V.

Best wishes
Bob

LCD-RELAY.png
LCD-RELAY.png1050×568 8.2 KB

4

But the moment the pins are connected to the relay, the LCD starts misbehaving.

Is that with or without the motor or fan being active. If yes then you have something wrong with your wiring and it is not wired like you think.

If it only misbehaves when the motors are running then it is lack of a diode across each motor and lack of decoupling capacitors. You also should not have the ground of your 12V common with the Arduino ground.