Today I soldered my 1602 display to an I2C 1602 adaptor. The display lights up, but I cannot get it to show any letters. Now looking at the LCD datasheet, again, I notice that pin numbering on the LCD is not 1,2,3...16, but more like 14,......,1,15,16. Does this mean that pins are not matching the linear wiring of the I2C adaptor?
I am using an Adafruit ESP32 board with Arduino Core and tried 4 or 5 LCD_I2C libraries and nothing changed. Here's how I soldered the I2C, I think it is positioned correctly, but maybe I messed something up? Or used a non-compatible with the I2C adaptor display? Also the last code I tried is here (Gist), but that changed nothing. I followed this tutorial.
You have answered your own question.
Match pins 1-14 between LCD and Adapter.
Snip off 15,16 from adapter and hand wire to 15, 16 on LCD.
Note that backlight anode, cathode sometimes get swapped.
Next time buy an LCD with 16 pin header at top left of LCD i.e. to match your Adapter.
Or better still, buy LCD with backpack already soldered.
David.
Thanks David. I suspected that this was the case, but I wasn't too sure (I am a rookie with the Arduino stuff). So I guess the pinout on the LCD looks like 14,13,12,11,10,9,8,7,6,5,4,3,2,1,15,16. At least it is Hitachi driver compatible. As you said, LCDs must have the pins in order from 1 to 16 to work with the I2C. I didn't know about that or the already soldered ones with the I2C until recently. Pity that most tutorials never point this out. If someone here has an audience, now is the time to let the world know.
What I will do now is to desolder the I2C from the LCD and place it on a breadboard. I have some male headers laying around and those will then be soldered to the LCD. Then I will just wire the LCD and I2C on the breadboard. Clumsy, but it'll work and will still look somewhat more portable and won't consume all of my GPIO ports.
Snip through the header with sidecutters. Then you can unsolder one snipped pin at a time.
The backpacks have consistent pin layout. Pin#1=GND, Pin#14=D7. Pin#15=LEDA. Pin#16=LEDK
Yes, it is probably wise to solder a new header on the LCD Pin#1 - 14. Test it on a breadboard.
If it works ok, solder it to pin#1 - 14 of the backpack. Flying wires for 15, 16.
Blue LCDs must have a backlight.
Green LCDs work fine in daylight.
I don't like Blue LCDs.
David.
Yep, will do that. I will let you know how it works out. Now I gotta find the time to go and buy some desoldering wick 
.
And yes, that LCD's back heats up pretty good with that backlight. Definitely not good if you want to use it with a battery in confined space, I think. But I will keep it powered via USB 5V just as a proof of concept for my project.
Don't try and desolder multiple pins at once. Solder-wick will not remove all the solder from plated through holes.
The LED backlight should not get warm. Measure the current.
The backlight should have series resistor(s). You can follow the copper traces from 15, 16.
Some LCDs have 0R mounted. You should have 100R for a sensible current. e.g. 20mA for white LED with Vf=3V
David.
