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Topic: Working LCD goes blank (Read 11783 times) previous topic - next topic


Hi everyone,

So after a long night with my project I have this bug ad don't know where it comes from... My 16x2 LCd is working great for a couple of minutes and then out of the bloom it goes blank¿?  I know te arduino UNO is still working because my PWM outputs are working and the relays also, the only thing is the LCD... Could it be im demanding too much current from the UNO?
Outputs are: LCD, 3PWM to transistors, 4 relay modules..

Thanks for the help


Not a lot to go on here.
It could be your code which you haven't posted or it could be your hardware and you have no schematic.

Try just a simple hello world and see if that runs without blanking out. Then you can move on from there.


Could it be im demanding too much current from the UNO?

More questions...
Have you tried monitoring the +5 Volt power pins to see if the voltage drops at about the time that the LCD stops functioning?

Does the LCD controller chip (or epoxy blob) get hot?

Does your display have an LED backlight?  If it does did you use a series current limiting resisitor with it?



As u said I'm missing info... The code is working good since it has been working for weeks, the relays were added yesterday before this it was all good. As don said I do have the backlight led on but with no limiting resistor could it e that with the added relays it causes this? What stranges me is that if I reset it, it works fine for 5m aprox. Then goes blank with the back led always on, jut blank characters. If I reset this will happen again...

Everything is soldered on the display and wired to the arduino so cables are fine... I'll try to put a limiting resistor or just plain cut the back led


What kind of power supply are you using and are the relays supplied from a different supply?. Do the relay coils have back emf suppression (a diode on each coil). Finally when you added the relays did you include extra bypassing for them?, it is usually required if for no other reason except the added current drain.

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"The solution of every problem is another problem." -Johann Wolfgang von Goethe
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I'm using a 12v @1A power supply for the arduino, th really module uses optocouples for every relay, I figure this would enough protection and didn't add diodes or anything, the module itself includes them. I don't know If it's in appropriate but here is the link from here I purchased the relay, the sexing picture has a schematic, where you can see all the components.



The code is working good since it has been working for weeks, the relays were added yesterday

So you added no code when you added the relays?
If you did then you have not got code that has been working for weeks.

Asking for a second time for a schematic, don't make me ask again.



I dont have a schematic but i can enlist where every pin is connected to:

IOREF: nothing
3.3v: nothing
5v: 4x relay modules (sch below), LCD VCC, LCD backlight (no resistor), LCD contrast with 10Krstor, 1x2n2222a collector pin, RTC ds1307 VCC,
GND: shared with 3x2n2222a, 4x relay modules, LCD, RTC ds1307 VSS

A0-A3: nothing

Digital PINS:
D0: relay1
D1: relay2
D2: nothing
D3: 2n2222 base pin (PWM output)
D4-D7: LCD
D8: relay3
D9: reserved for relay (already connected)
D10: 2n2222 base pin (PWM)
D11: 2n2222 base pin (PWM)
D12: LCD
GND: nothing

Schematic of the relay (I have two of these modules hooked up)

Video of the behavior:


it wouldnt let me post the code in one single post sorry

At the bottom of the reply box is an arrow that says additional options. Click that and include your code file. Delete the other posts with part code in them. Then people can see the whole of your code.

The back light stays on so that means you still have power.

LCD backlight (no resistor),

Fix that NOW before you blow anything up.

Put diodes across the relays.

Add some decoupling to the supply:-


ok, thanks!

complete code:


Does this code compile for you? I get errors.


Yes the code compiles no problems! Maybe ur missing a library? what errors do u get?


No I have all the libraries I get:-
original_sketch_inverted.cpp: In function 'void setDateDs1307(byte, byte, byte, byte, byte, byte, byte)':
original_sketch_inverted:112: error: call of overloaded 'write(int)' is ambiguous
/Users/mikecook/Documents/Arduino/libraries/LCD_I2C/Wire.h:55: note: candidates are: virtual size_t TwoWire::write(uint8_t)
/Applications/Arduino.app/Contents/Resources/Java/hardware/arduino/cores/arduino/Print.h:49: note:                 size_t Print::write(const char*)
original_sketch_inverted.cpp: In function 'void getDateDs1307(byte*, byte*, byte*, byte*, byte*, byte*, byte*)':
original_sketch_inverted:135: error: call of overloaded 'write(int)' is ambiguous

Are you using IDE 1.0.1


My 16x2 LCd is working great for a couple of minutes and then out of the bloom it goes blank¿?

If it still doesn't work after dealing with the backlight current then you should investigate what else may be happening to cause the LCD to go blank.

I have a feeling that this behavior is related to something other than time, most likely the activation or deactivation of a relay.  Mike has already pointed out that you need to make sure that you have diodes across each relay coil and he has given you a link to his information concerning decoupling.



Yes Im using IDE 1.0.1 to compile.. You seem to be having trouble with the Wire library to communicate via I2C with the RTC ds1307, do you have the library in the arduinos libraries directory?

I added a 0.1uF ceramic capacitor across the +/- to eliminate noise from the PS and resitance to the LCD backlight LED as you indicated mike, but still no luck  :(

Don, the relay modules already integrate protective diodes and are also activated via optocouplers which makes me think another diode would be unnecessary, did u see the schematic of the module? If so should I still add another diode?

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