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Topic: LCD Strange Characters! (Read 552 times) previous topic - next topic


Good evening, I'm doing a project to heat an incubator, but I'm having a little problem. I'm using an arduino uno, a 4 relay module,  DHT11  temperature and humidity sensor, and a 16x2 LCD.
This should work like this, when the temperature is below or equal 31 Celcius one light bulb (220V) connected to the relay module will turn on and heat the incubator and when the temperature is higher or equal than 33 Celcius the light will turn off. But when the system is working for some among of time the LCD display start to display strange characters, but the circuit sill working fine, just don't display the temperature and humidity.
Maybe some one had de same problem and know what is happening? I would thank some help!

Sorry for my English, Naff16

jack wp

when the system is working for some among of time the LCD display start to display strange characters
What amount of time?
Is the LCD close to the light (does it get hot)?
Are the grounds and other wires to the LCD connected securely, or maybe through a bread board?
Try adding some caps around (.1mf range) on power pins (ground and +5V).

Curious, what are you trying to hatch?
Good luck, Jack


Less than 1 day, and some times when the light turn on, the strange characters appear!
The light is far from the LCD and the rest of the circuit, all the gnd are the same connected on the breadboard. Maybe some interferences, because the breadboard or other wires? This just happen when the light is connected, if i switch off the light the lcd work fine.

jack wp

What watt bulb is that? Maybe try a smaller watt bulb, and some extra caps around.

Are you running the arduino and the lights off a small extension cord? If so, split them up. Use a different AC plug for each.

Rather than a mechanical relay, you will get less noise by using SSR designed for AC.

If you have to user mechanical relays, make sure you have protection diodes, snubbers, and proper drivers for it.
Good luck, Jack


I will make some test with some smaller bulb and some extra protection arroung and see what happen :)
The relays im using are in a 4 relay module they have all protections, etc..
Maybe when the light goes on, some kind of interference happen.. dont know, i will make some tests again. Thanks!

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