LCD Display Problem

Dear all,

I am trying to control a 1hp motor through the 230VAC contactor which is controlled by a 12v relay supplied with 12v 1A SMPS Adapter.

Everything works fine if i disconnect 230VAC Contactor. but when i power it up, the lcd displays random characters and after few attempts all the disappears. however arduino works fine as the logic executes perfectly.

When i checked voltages across the lcd supply pins, i obeserved that there are some spikes that are generated whenever the contactor turns on or off. measured voltages are nearly 17v DC, 6v DC, 10v DC etc. I have traced the problem but don't know how to resolve it.


  1. Earthing and all the ground pins are earthing problem is found.
  2. No motor trial is taken as the problem appeared when contactor connected.

The noise on the line is trashing the display. Power the LCD from battery and see if that eliminates the problem. If not, then try powering both the display and the arduino from a battery instead of a power supply running off ac. This is a common issue.

Add a snubber circuit to the motor. Leo..

Hi, The best to way to turn any AC device it is the use of solid state relay commonly name as SSR. Since the input to the SSR it is done using an optical couple it will isolate the micro from any AC interference coming from the relay contact. As one of the member already advised you to prevent the contact noise is the use of snubber across the relay contact. This is done by using a resistor in series with a capacitor across the relay contact. Typical snubber it is a 100 ohms resistor in series with a .01uf capacitor. If you want learn how to use snubber do a google RC snubber.

Hi, I forget to mention that another simple solution it is the use of a varistor across the relay contact. i would use one about 350 volts AC.

Try just by connecting 0.1uF capacitor across (near LCD) Pin-1 and 2 of the LCD. It should kill the spikes coming from the MC's operation.