Troubleshooting for common LCD problems

[per1234]

I believe there are certain common LCD problems that have specific symptoms (e.g., white/black blocks). I remember seeing a nice guide about this, maybe on Stack Exchange.

Symptoms

• One line of squares:
  • references:
  • https://forum.arduino.cc/index.php?topic=672583.msg4527945#msg4527945
  • https://forum.arduino.cc/index.php?topic=674447

Problems

• Contrast setting too high or low (many LCDs come with the pot set to a position that causes no display).
• Incorrect I2C address.
  • The Wire library has an I2C scanner example
  • https://github.com/duinoWitchery/hd44780 automatically detects the I2C address
• Incorrect wiring (e.g., assuming A4 and A5 are I2C pins on boards where this is not the case).

Reference:

• https://forum.arduino.cc/index.php?topic=680452
• https://forum.arduino.cc/index.php?topic=665383
• https://forum.arduino.cc/index.php?topic=660594
• https://forum.arduino.cc/index.php?topic=666006
• https://forum.arduino.cc/index.php?topic=665971
• https://forum.arduino.cc/index.php?topic=667221
• https://forum.arduino.cc/index.php?topic=668114
• https://forum.arduino.cc/index.php?topic=671871
• https://forum.arduino.cc/index.php?topic=676641
• https://forum.arduino.cc/index.php?topic=700246
• https://forum.arduino.cc/t/lcd-i2c-does-not-work-checklist/637380