Today my LCD with keypad shield arrived, which I needed for a project. The only problem is, it's only displaying white rectangles on the display and no letters. I browsed the internet and came to the conclusion I needed to lower the contrast, but how do I do this?
Hi THeerze, welcome.
Would you believe me that this question is among the most asked questions on this forum ?
So do a little search, perhaps using google, and narrow its results to this section of this forum.
I bet your answer can be found right there.
Look for an answer by Floresta, he's given lots of thoughts on the LCD (contrast) subjects.
Here I am, a little late to the party.
... but how do I do this?
You lower the contrast by means of a potentiometer that allows you to vary the voltage at pin 3. On a shield it is usually a rectangular device about 1cm or 1/2" square with a plastic screwdriver slot on the flat face. It could also be a multi-turn device with a metal screwdriver slot on one edge.
The only problem is, it's only displaying white rectangles on the display and no letters.
As far as the white rectangles go:
- If your display has white rectangles at all of the character locations then you have a contrast problem.
- If your display has white rectangles on alternate lines and is blank on the others then you have a wiring and/or a programming problem.
Don
floresta:
As far as the rectangles go:
- If your display has white rectangles at all of the character locations then you have a contrast problem.
I did find out it was a problem with the contrast, because the rectangles were showing on the complete screen.
floresta:
You lower the contrast by means of a potentiometer that allows you to vary the voltage at pin 3. On a shield it is usually a rectangular device about 1cm or 1/2" square with a plastic screwdriver slot on the flat face. It could also be a multi-turn device with a metal screwdriver slot on one edge.
I didn't find the rectangular device on my shield, can I still do something on it?
By the way, I'm also using an Arduino based board (WeMos D1) instead of a regular Arduino. Could this also cause trouble?
I didn't find the rectangular device on my shield, can I still do something on it?
It's the blue device in the upper left corner. That looks like a multi-turn (probably 20 turns) device, stop turning when you hear or feel the clicks.
By the way, I'm also using an Arduino based board (WeMos D1) instead of a regular Arduino. Could this also cause trouble?
Yes it could, not because it is an ESP8266 device but because it runs on 3.3v and your LCD probably is specified for 5v. The LCD controller will likely be happy with the 3.3v but the display itself is a different story.
For a normal temperature range LCD the voltage at pin 3 is typically specified as being about 4.5 volts less than the voltage at pin 2. In other words the voltage at pin 3 is not specified with respect to GND which is the way we are used to dealing with such measurements.
Normally, with a 5v supply this puts the voltage at pin 3 at about 0.5v above GND. When you run the same LCD at 3.3v this means the voltage at pin 3 should be around 1.2v below GND (aka -1.2v). If your LCD is an extended temperature range device the situation just becomes worse!
Don