LCD screen won't display anything

What happens when you adjust the contrast pot?

Go on. Let's see six signal wires + GND, 5V clearly going from breadboard to Uno.
With a few neat breadboard wires connecting RW, LED-, LED+, VO to GND, 5V, potentiometer.

Incidentally, you could connect VO pin straight to GND. Forget about the pot.

The fewer wires that you use, the less likely that you connect them wrong.

David.

here you go:

Your potentiometer is still not wired properly.

bad lcd pot

I finally what se @LarryD is saying (caffeine kicks in). The pot is not connected to anything because the breadboard is being used improperly. That means that Vo is floating. OP, please do as @ david_prentice says and connect V0 (LCD pin 3) to ground and let us know the result.

Thanks a lot the boxes on the LCD screen are showing now

On your breadboard turn the pot 90° and wire as shown here (yes, they both go to ground):
lcd pot wiriing

Then you should be able to adjust the contrast.

OR

2021-10-09_11-06-44

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Thanks a lot for the help I was able to make the project of my humidity and temperature sensor. Once again thanks a lot.

No, see #3!

It's not an "intensity" setting, it is a contrast setting. And for an "alpha" display, it is not something you vary to taste, but rather always adjust for the best contrast.

well, it was solved while I slept. Saves me any embarrassment about not looking at the photo in #4 and missing the oh-so-obvious blunder! :grin:

When you connect both 1st and 3rd terminal to GND, what's the use of a pot? It'll simply be 0V.

I have tried the old schematic and it worked just fine.

Yes, if you turn the potentiometer to either end. But the problem here is that people frequently make comments having no understanding of how the contrast control works.

Vo connects to the end of a resistor chain of 2k2 resistors - "R1" to "R5" marked "222" in the module, totalling 11k, the other end of which connects to Vcc.

Yes, of course it "works" - sort of, otherwise the mistake would not have been propagated again and again over years.

It just does a very poor job in two respects. One is that the valid adjustment is all the way down one end of the potentiometer range, less than 10% usable.

The second is that it wastes 500 µA. You say "what does that matter"? Well, the actual LCD display with no backlight only draws about 1 mA in the first place, so that is an additional 50% power wastage.

So the proper connection is a 1k pot wired as a variable resistor between Vo and ground.

This will spread the valid contrast adjustment range over most of its span. But if you only have the unfortunate 10k potentiometer, then not connecting it to 5 V actually doubles the workable range and connecting both ends to ground halves its value and almost doubles the workable range again!

or if you buy a LCD I2C SERIAL ADAPTER it will help.