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I2C causes IoT pHAT to fail

#1

I have an LCD screen connected to the I2C interface and it causes the IoT pHAT to fail. At least I can tell that the WiFI fails. I thought that the I2C is not used by the pHAT.

What I did to narrow the problem down was to start without anything connected. The pHAT WiFi connects to my network. I then SSH to my Pi. I then connect my LCD to the I2C. The moment I try to run my LCD program, the WiFi fails and I lose connection.

Any ideas what the issue could be?

#2

Does the LCD screen use other pins besides the I2C interface?

#3

Only the 5V and GND pins. No other I/O pins.

#4

Hi, we want to buy one I2C screen to test, would you mind to give us the information?
We also tried with an I2C EEPROM, but we cannot write data to it even without the IoT pHAT.

#5

I use this http://www.ebay.com/itm/Serial-IIC-I2C-Adapter-1602-1604-2002-LCD-Backpack-Arduino-FAST-SHIP-US-SELLER-/171036006949?hash=item27d28a5a25:g:vNIAAOSwMmBVnc7K

This will connect to most LCDs that uses the Hitachi compatible interface HD44780.

#6

The LCD is 5v, but the Pi is 3.3v, could you check the LCD’s I2C is 3.3V or not?

#7

LCD I2C is powered at 3.3V. The I2C expander chip on the LCD backpack has a wide voltage operating range so it can work at 3.3V or 5V. There is a slight modification required for the LCD backpack so that the LCD display contrast is better and the backlight is brighter for the Pi otherwise it the display will be hard to see. I use 5V for the backlight and LCD contrast control. This is isolated from the I2C.

#8

Is this problem solved?
I would like to use a pi zero with the iot hat and the I2C simultanious in one project.