PIC Microcontrollers with C18 Compiler

PIC Microcontroller

The microcontroller used for this project is the PIC18F4431 made by Microchip. This is an 8-bit microcontroller with motor PWM generators, a quadrature encoder interface (QEI), and other "peripherals". The microcontroller uses an external 40MHz oscillator.

The microcontroller controls two wheel motors with PWM driving external H-bridges. The H-bridges draw their power directly from the batteries, not regulated power.

Each of the wheels also has a quadrature encoder. The left wheel encoder is connected to the PIC's QEI via a schmitt trigger buffer. The right wheel encoder is wired to a U.S. Digital LS7183 chip (because the PIC only has 1 QEI) which outputs pulses on one of two pins, depending on whether the wheel is spinning backwards or forwards. The two pins are then each connected to a counter on the PIC, which keeps track of the number of pulses. The location of the wheel can be determined by subtracting the reverse-pulse counter from the forward-pulse counter.

The PIC is interfaced with the XBee modem via the RS-232 serial interface.

Programming the PIC

For this project, Microchip's free MPLAB IDE and free C compiler were used to program the PIC18F4431. If you are using the ICD2 programmer, be sure to follow the installation instructions carefully, or Windows may attempt to install the wrong drivers. After installing both MPLAB and C18, create a new project with the project wizard. Follow the prompts, and you should end up with an empty project if you did not add any existing files.

We must now add a linker script to your project. Make sure View>Project is checked, then right-click on Linker Scripts in the project panel and click on Add Files.... The linker scripts are in folder MCC18\lkr. Find the file that corresponds to your microcontroller (p18f4431 (or p18f4431i if you are using the ICD2 programmer) for the PIC18F4431 microcontroller).

We now add source and header files in the same manner. With the default settings, all the source and header files must be in the same folder or the project will not compile. In your main source file, you should include the line

#include <p18f4431.h>

Troubleshooting

• If MPLAB has trouble connecting with the ICD2, open the Device Manager (Control panel>System>Hardware>Device Manager) and disable then re-enable the ICD2. Also be sure that you followed in installation instructions in the manual when you installed the ICD2.