LCD HD44780 I2C-adapter

LCD display, based on HD44780, is very popular. There are many types of such displays, with different resolution from 8x1 symbols to 20x4 symbols. But all of them used to connect to the microprocessor for at least 7 control lines, excluding the lines backlight incorporating. It is very wasteful. To reduce the number of control lines to the 2 lines LCD can be used connection to the I2C bus, and still be able to use the bus by other devices. For this purpose can be used remote 8-bit I/O expander for I2C-bus PCF 8574.

Step 1: Two type of PCB's

There are two type of LCD based on HD44780 - with one row of 16 pins with step 2.5 between pins, and with two row of pins 8x2 with step 2.5 between pins in row and in column. For that reason, project have two type of PCB's in one board - for each type of LCD we cam use his own type of PCB.

Besides, each PCF8574 has three lines for addressing it - A0, A1, A2. In our project we use only adress line A0, that can be switch to 1 (by default) or 0 by using switch. We think, that use more than two LCDs in one I2C-bus - too beautiful :)

In addition, forswitch on/off backward light we use one transistor, included in circuit with common emitter.