This tutorial continues from Character LCD Displays - Part 1. In this part we will connect the LCD module to an Atmega8 microcontroller, then write some code to drive it.
Our first task is to build the circuit.
We will be using an AVR 28 pin Development Board. For the power supply we will use a USB to DC Barrel plug cable, so we won't need to build a 5V regulator circuit. Instead we will run a wire from the barrel connector to the positive power rail, as shown in the photo below.
Also we won't need an external crystal or AVCC filter block. We still need to run power to AVCC and this is done with a piece of wire.
Because we want the ability to remove the LCD module later, we will solder a 16 pin female header to the board.
Next we wire-up VDD and BLA to the positive power rail along with VSS, RW, D0, D1, D2, D3 and BLK to the ground power rail. D0 to D3 are being tied to ground because we will drive the display in 4 bit mode. This lets us drive the display with just 6 I/O lines.
Next we add a trimpot for the LCD contrast. I used a 5K pot, but a range of other values would work as well.
We now connect RS, EN and D4-7 to PC0-PC5. These could have been connected to any of the atmega8 I/O ports, but port C seemed to be ideal as it has 6 usable I/O pins. If you decide to use other pins just change the source code accordingly.
As with the Breadboard example we will solder a 16 pin header to the LCD module.
Lastly we attach the module to the female headers.
Coding - Part A
Our first "Hello World" program is below. We are following almost the same series of steps as the 4 bit example in Part 1.
Coding - Part B
The previous example is fine, if all you want to do is understand the principles of how LCD displays are driven, but in practice coding in this manner is a bit painful. To make things easier we need to abstract away the finer implementation details and focus on the operations the developer needs to perform. The easiest way to do this is use a pre-existing library.
A very popular HD44780 AVR library is Peter Fleury's LCD library. This library is very good but I'm going to use alank2's slimmed down LCD library instead. My reasons are:
To use alank2's library
Using alank's library we create the next example program. This program does much more than our previous "Hello World" example and is only 30 lines of code.
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