LCD with (ESP32) Wemos D32 voltage problem

Hi all,
I'm connecting my Wemos D32 pro to the classic 16X2 LCD display.

I've connected all the wires correctly (the text "Hello World" appears) but the contrast is very low.

I've also tried to adjust the backlight with the A and K pins but in my opinion the problem is that the VDD needs 5V and my board can only give out 3.3V.

Do you agree with my hypothesis?
Do you have any suggestion?

Thanks in advance

Yes, the contrast (pin#3) needs to be about 4.5V below VCC (pin#2)

The LCD will work fine with 3.3V logic. Connect VCC pin to 5V

If you do not have a 5V supply, you need to provide -1.0V to pin#3. (e.g. via a diode pump)

david_prentice:
Yes, the contrast (pin#3) needs to be about 4.5V below VCC (pin#2)

The LCD will work fine with 3.3V logic. Connect VCC pin to 5V

If you do not have a 5V supply, you need to provide -1.0V to pin#3. (e.g. via a diode pump)

So it should work giving 3.3V to pin #2 and -1V to pin #3?

(could you explain to me the procedure to have that negative voltage?)

It looks as if the VBUS pin (USB) at bottom left of your board is 5V direct from USB connector.

Just use this 5V source on pin#2. Then the contrast will work like with a regular 5V Arduino.

If you want to generate -1.0V ask Wikipedia about "diode pump" or "charge pump".
You provide a PWM signal to diode-resistor-capacitor circuit.

Believe me. VCC=5V on pin#2 is a lot easier. Use write-only LCD code. There is little point in read-busy code. But I suspect the HD44780 is pretty wimpy when it comes to output and is unlikely to harm 3.3V ESP32 with busy-read.

David.

Perfect! you're right about the USB pin,
thank you!