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I am having trouble getting characters to display on my Adafruit 16x2 blue/white monochrome LCD + keypad. I am wondering how best to isolate the problem as either hardware or software. It shows up in i2cdetect, and the screen can be turned off and on, but the only characters that show up are the default "filler blocks".

  • Raspberry Pi model B
  • The display/keyplate is product 1115 on Adafruit (I can only have two links or I'd link it)
  • Raspbian latest

Troubleshooting attempted:

ic2detect -y 1

shows the device at 20. I am following the directions at https://learn.adafruit.com/adafruit-16x2-character-lcd-plus-keypad-for-raspberry-pi/usage and everything seems fine up to

sudo python char_lcd_plate.py

This turns the backlight on and off (which is expected because it's actually trying to cycle backlight colours that don't exist on my monochrome display). But no words are ever displayed on the screen. The keypad is definitely working because I changed line 73 to read

print button[1]

and it displays correctly which button is being pressed.

Since the backlight is toggling and the switch status can be queried, it can be established that data is definitely flowing between the Pi and the expansion board. But no characters are being displayed. How do I figure out whether I should be troubleshooting the hardware or the software?

  • Maybe a stupid question but have you adjusted the contrast. It may be working correctly but the contrast adjustment is making it appear like a blank screen or one full of the blocks you describe. – Steve Robillard Apr 15 '15 at 17:47
  • We've ramped the contrast pot up and down, it's definitely showing "blocks", not letters. – Monban Apr 17 '15 at 2:11

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