I am using a number of 'rescued' 1602 and 2004 displays. with a I2C interface board connected.
I am using Malpartida's NewLiquidCrystal library.
The display works fine apart from the fact the backlight doesn't work?
I have lcd.backlight(); in setup.
If I put a voltage tester on pins 15 and 16 of the I2C interface board I get 5v but 5v on pin 15 and gnd on 16.
If I put 5v on pin 16 and gnd on pin 15 of the display the backlight lights.
I have three displays and two I2C interface boards and they are all the same.
Are my interface boards wrong or the displays?
I don't think my problem is the same as bperrybap's on this page.
ADD.
If I put the I2C and the display on a breadboard and just connect pin 15 of the I2C to pin 16 of the display and pin 16 of the I2C to pin 15 of the display the backlight lights? If I put noBacklight(); in setup the backlight goes off?
I would guess the LCD modules themselves were incorrectly manufactured with the backlight LEDs inserted the wrong way. If this affected a whole batch, they may have been sold off at reduced price to a buyer who was able to adapt their use to compensate.
I think you are right Paul. I have found two more displays and they both work with the I2C units? how odd. The bad ones are visually quite different and not from the same batch?
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