HD44780 LCD + MCP23008 I2C backpack not being detected via I2C

Projects Networking, Protocols, and Devices
1

Hi guys,

Using an Arduino MEGA I'm trying to run a HD44780 LCD display that has a MCP23008 I2C backpack and I'm having trouble making it work. I've tried the following (all on pin 20/21 since this seems to be a common mistake):

  • tested the LCD without the backpack and it works fine
  • adding some pull-up resistors to SDA and SCL
  • up to date libraries, and various I2C scanners

All I2C scanners i've tried didn't find the device. Any ideas?

Thanks.

2

When no I2c scanner is working, there is no valid I2C bus.

Your board: http://arduino.cc/en/Main/arduinoBoardMega2560
Is this your shield ? i2c / SPI character LCD backpack - STEMMA QT / Qwiic : ID 292 : $9.95 : Adafruit Industries, Unique & fun DIY electronics and kits
Is this the i2c scanner that you have run ? Arduino Playground - I2cScanner

For the mega board, pin 20 is SDA and pin 21 is SCL. Both have already a pullup resistor on the mega board of 10k to +5V.

Are you sure the shield is in I2C mode ?
Can you upload a photo with the wires ?