16x2 LCD Letters Are Very Dim

[Judd]

I have connected an LCD to my Particle Photon, and the letters that the Photon sends appear to be very dim. When connected to my Arduino, they are fine. I think it has to do with the fact that the Photon is 3.3v, so I put a 3.3v to 5v logic level converter on all the digital outputs, but it still appears dim. Whenever the LCD freaks out and displays random letters and question marks, the text is bright and easily readable. I can send pictures if that would help better. Thanks, for any help.

[WereCatf]

21 minutes ago, Judd said:

so I put a 3.3v to 5v logic level converter on all the digital outputs, but it still appears dim.

You need to supply the LCD 5V on the VCC. Supplying 5V on the GPIO-pins isn't going to make it brighter.

[mariushm]

The contrast of the digits is set using a potentiometer, between 10k and 20k ohm on most 16x2 displays. You can use two resistors instead of a potentiometer, once you get the right contrast value.

Here's an example datasheet with the most common pin layout and how to wire it : http://www.newhavendisplay.com/specs/NHD-0216K1Z-FL-YBW.pdf

 

These displays need 5v to work. If you use level shifters on the input pins, my guess is the microcontroller will power itself from the io pins instead of the vcc pin which is only 3.3v ... so it starts to work, but the current amount supplied through the io pins is too small to give you high contrast.

 

IF you want something super simple and relatively cheap, you can use a voltage doubler IC - it's cheaper that a full blown step-up/boost regulator (if we're talking through hole, there's some cheap <0.5$ synch. step-up regulators that only need an inductor and a couple ceramic capacitors to work but they're surface mount)

 

For example TC7660 from Microchip or *7660 from others: https://www.digikey.com/product-detail/en/microchip-technology/TC7660EPA/TC7660EPA-ND/442707

If you don't mind surface mount, there's TCM828 or LM2681M6X or others (filtered list).

So you can use one of these to boost 3.3v to 6.6v minus the voltage drops on the 2 diodes you'll use so if you go with 1n400x diodes which have around 0.5-0.8v drop per diode, you end up with less than 5.5v on the output.

 

 

[Judd]

17 hours ago, WereCatf said:

You need to supply the LCD 5V on the VCC. Supplying 5V on the GPIO-pins isn't going to make it brighter.

When I connect the LCD to an external 3.3v power supply it appears dim, when connected to a 5v power supply all of the individual pixels are whited out.  When connected to the Arduino and 3.3v it works perfectly fine. When connected to 5v it still appears whitewashed.

[Judd]

Ok, sorry about this but it appears after some testing that my 5v power supply was outputting 10v instead of 5v. So, after getting a new power supply and testing it, it now works. Thank you for the help and sorry for wasting your time. Have a good day.