Figure 1: AVR Guitar Block Diagram

While using both electrical circuitry and C code programming of the micro controller, the project was dissected into smaller divisions that could be analyzed individually to ensure the overall project functionality (Figure 1). The electrical hardwiring of the switch, 7-Segment LED, and fret board LED’s were the first to be constructed to provide the controller with input and output paths. As this was completed, the program code could then be executed. To keep the program as short and memory efficient as possible, while statements were used to read in the inputs from the switch and output to the 7-Segment and fret board LED’s. These statements provided an effective way distributing which outputs were on/ off from a given input.

The declarations and initializations of the program describe the port setups and pull up resistors. After falling through, the program then reads in the values of the 12-position rotary switch and checks for a logic zero because of the pull-up resistors. From the read on the input port, the program will jump to the dedicated while loop which will tell the program what pins will output a logic high (+5v) value. The outputs are divided into two “sections” – one dedicated to the 7-Segment LED and the other to the fret board LED’s.

Figure 2: 7 Segment Pinout

The 7-Segment output (Figure 2) is a standard output device displaying the note letter and whether or not it’s a sharp. The fret board LED output continues on to a transistor buffer circuit that needs to condition the current and increase it over 6-LED rungs. To do so, 12 standard Emitter Follower transistor circuits were used to obtain the right amount of current to drop across the 6-LED rungs. The transistors used were 2N222 NPNs, a calculated 18Ω emitter resistor, and a 2.4k Ω base resistor to obtain 60mA across the each rung of LEDs (Figure 3).

Figure 3: AVR Guitar Transistor Circuit