The 2 line LCD display.

A 2 line LCD display can be used to display simple information. When using an ADC to read voltages it can be used to show the results implementing like this a simple voltmeter.

The display is driven by a HD44780 display driver from Hitachi. The data sheet explains all the details of this controller. The controller can be directly accessed through GPIO lines, which however requires quite a bit of cabling. The other possibility is to pass through a pcf8574 I2C I/O expander, in which case only the I2C connections SCL, SDA, Vcc and GND are needed.

The 2 line LCD display	Its I2C interface

The blue potentiometer you see on the I2C interface is used to control the display contrast and, at least in my case, must be set to maximum contrast to see the text clearly.

The HD44780 can operate in 2 modes:

• a 8-bit mode in which all 8 interface bits are used as data and additional I/O lines are used as backlight control, R/W, strobe and register select lines.
• a 4-bit mode where the data bits are transferred in 2 successive cycles on the upper 4 data lines (D4-D7) while the lower 4 bits are used to drive the control lines

Our I2C interface uses the 4-bit mode and is connected as follows:

-- Uli Raich - 2017-02-01

Comments