LCD dim and 5V Vin not correct

Had a recent problem with the graphic LCD going dim when heaters are on ( bed or hotend )

Ramps 1.4 on Mega with Marlin.

Have tried reverting back to a version of marlin before I added an additional extruder - no change.

Now notice that the LCD appears to dim slightly just after the Marlin splash scren.
Also reverts back to full contrast when I press the reset button.

Suspected it may be code related so reflashed with the version before I added the second extruder. No change.

What I did find, was that the LCD stays on full contrast if I leave the usb connected to the laptop.

Does this mean that the voltage regulator on the Mega is at fault ?

Checked some voltages :
input to ramps from psu = 12.3V
diode D1 ramps side = 12.3V
diode D1 mega side = 11.5V
Ramps interface PCB for LCD, on Ramps Aux3, 5V pin for LCD reading 4.5V

Reading on the Mega Pins :
Vin = 11.5V
5V = 4.57V
3V3 = 3.26V

If I connect the USB to my laptop, the LCD contrast remains bright ( correct )

Edited 2 time(s). Last edit at 04/08/2017 06:02AM by DaveOB.

Maybe your voltage regulator is weak on your arduino? Most lcds pull just slightly more current than this regulator is happy with. Maybe supply usb power via a phone charger and the USB port or other 5v pin?

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

so this would indicate that the 5V regulator on the Mega is faulty ( weak / damaged ) and when the Mega is first powered, has enough current to power the large LCD.

But once the Marlin has initialised ( after the splash screen ), then the current available for the LCD is lower and causes it to dim ?

I guess the best option would then be to power the LCD from a seperate 5V supply ( like a Buck Convertor ) so that there is no large current drain from the Mega just to run the LCD ?

If so, would I be able to cut the LCD interface PCB's pin A10 and add the Buck Convertors 5V output there, and tie the Buck ground to the ground on Ramps ?

It might dim after booting as various things power up like stepper drivers etc...

Supplying extra 5v should help whether you need to cut the supply to the lcd I don't know try it.

You could solder a better regulator like an lm7805 to the mega.

Edited 2 time(s). Last edit at 04/08/2017 06:43AM by DjDemonD.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

Quote
DjDemonD
You could solder a better regulator like an lm7805 to the mega.

That I can do, but are the other parts and tracks of the Mega strong enough to power the LCD ?

Would it not be better to still ( also ) power the LCD from a seperate Buck Converter ?

I've had limited success using a USB charger supplying a graphical Lcd directly. It's not the tracks on the mega that aren't up to the job it's just the voltage reg. I'm using a rearm now which has a much better regulator.

Edited 1 time(s). Last edit at 04/08/2017 07:02AM by DjDemonD.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

OK. Update

I have added a buck converter ( set at 4.9V ) from the psu to the LCD +5V line, and the Ground of the Buck to the Ground of the PSU output, so the grounds are common.

Powered on and there was no contrast dip after the splash screen, and the LCD is bright and clear.

Started a print ( so bed and nozzle heaters on ) and LCD has remained stable.

I know that at some point I should upgrade the Mega voltage regulator to the LM7805 that is sitting on my desk, but think that it should manage 'as is' for a while still now that the LCD is not pulling current from the Mega anymore.

Thanks for the help.

Minus Lcd the default regulator is up to the job.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

I have always used a powered hub for the USB.. it's a simple solution that happens to give me more USB ports. I then removed D1 (or more accurately the pin going to the Vin socket on the mega) to prevent the 5v regulator on the mega receiving any +12v power) The Arduino relies solely on the +5V from the powered hub. Use a 5v psu of around 2A and all the arduino regulator problems, and dim/no display problems go away......or use your buck converter...