3-Wire LCD

LCD’s can use up quite some data lines on an arduino. Fortunately this can be reduced as most LCD’s can work in a 4 dataline mode. It can however done with even less datalines, using a shift register:


I admit that I have been inspired by LadyAda’s ‘I2cSPI backpack’ but since I only needed the SPI mode and the pin lay-out of my LCD module was different from the LadyAda backpack. I decided to just make my own. To use this circuit one needs to install the proper LCD library.

The variable resistor can be replaced by the diode and R2. 0,65 is often the optimal voltage for the brightness. R1 and T1 are not really necessary if you do not have a backlit display (these usually come with 16 pins).

Interesting reading from Carlo Denaro can be found here. He uses  pin D10 (to 14+RS pin), D9 (to 12) and D8 (to 11)  and uses IC pin 2 for the Vlc.

More 3 wire solutions, and here

3 Wires still too many? Well, how about two wires, here too?  Some more circuits here

How about one-wire?