LCD in car shows random characters scrolling

Hi!

I am using my arduino in my car and the LCD (HD44780) is starting to scroll random characters fast when the engine is running. I think this is something voltage related issue. The Arduino Mega 2560 R3 (chinese clone) is connected though the power input socket and it connects to the radio's +12V. When the engine is running it is around 13-14.4Volts, so maybe thats the problem.

Should i use a voltage regulator with capacitors to create a more stable voltage, like 8-10V? Or do you have any other suggestions?

Thank you.

You need an automotive noise and surge suppressor circuit between the 12V socket and your project.

The electrical system in a car is extremely hazardous to electronics, with possible polarity reversals and voltage spikes occasionally exceeding 600 V.

Normally, Instructables are complete crap, but this one describes a possibly useful automotive surge suppressor that you can try.

And anywhere near the ignition system you pretty much need full shielding for all boxes and cables - 25kV pulses are not forgiving. This is a likely route for random garbage being picked up by your LCD.

You don't say just what you are doing with the Arduino in the car, but if you have any inputs connected to anything in the car, you need signal conditioning on them. As others have noted, the automotive environment is typically very noisy with all sorts of spikes (you can get some really nasty spikes on the 12 volt line when the starter is in operation). You also need to make sure you have a good ground if you are measuring other things in the car - different "grounds" in the car can have significant non-zero voltages on them periodically.