(3 Reviews)
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Modification needed before use 
I ordered two of these for some projects where I need a display and some simple inputs.
I opened one and tried it with the sample LCD code in the Arduino IDE. Backlight came on and it appeared to be working. I couldn't see any text though. So I adjusted the contrast trimmer pot, which I thought was freely spinning (it wasn't), but that led me to a post about some faulty designs on this type of 16x2 LCD shield.
Someone wrote a sketch to test if the backlight circuit was a faulty design -- and these shields fail that test. I had to desolder the LCD board from the shield and then cut a trace between Pin 10 and the transistor under the LCD (and add a 510-ohm to reconnect the pin to the transistor).
Without this modification, you can burn out pin 10 on the Arduino, if the pin is set a certain way, as the transistor will pull too much current from the pin in certain states. Post to explain the issue:
https://forum.arduino.cc/index.php?topic=96747.0
Got it working - contrast pot
I got these intending to use with a Raspberry Pi for a simple thermostat project. I thought these would be great, since it has both the LCD and built in buttons!
TLDR; The blue contrast potentiometer in the corner was set so low the text was invisible. It took many rotations in the clockwise direction before I saw any text appear.
I had some trouble at first, as I connected everything up and didn't see any message displayed. Backlight worked, but no message. I checked by connections, disconnected and reconnected everything, double-checked my code, and scratched my head for a few days.
Since it was designed for an Arduino and there's example code for that, I tried plugging it into one I had around. Even that setup didn't show any text. I eventually tried what the other reviewer suggested and installed a diode on the board, thinking that sounded plausible, and it STILL didn't work. That led me to start messing with the contrast pot, and lo and behold, after turning it a bunch I start to see text! The blue contrast potentiometer in the corner was set so low the text was invisible. It took many rotations in the clockwise direction before I saw any text appear.
I can't say I've used these weird blocky potentiometers before, so maybe that's a common thing one might expect to adjust before seeing any output. A little warning would have reduced my frustration, so that's why I'm leaving this note here. Hope it helps someone else!
Beyond that issue, the display is pretty great. It's a nice condensed package and should make for a great interface for projects.
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