EDP-mbed Demo with SRF08 and DC motor

Page last updated 03 Feb 2011, by William Marshall. 0 replies DesignSpark, RS EDP, RS-EDP, SRF08

// EDP & mbed demonstration program using I2C and PWM: WGM 2010
// Uses SRF08 Ultrasonic Range Finder on I2C address 0xE0
// Option link J217 on EDP mbed carrier changed from 1-2 to 2-3
// Jumpers on EDP MC1 module will require setting to suit GPIO signals

#include "mbed.h"

I2C sonar(p9, p10);                         // Define SDA, SCL pins
Serial pc(USBTX, USBRX);                    // Define Tx, Rx pins
PwmOut motor(p23);                          // Define PWM output (EDP: EVG0_GPIO40)
DigitalOut Brake(p19);                      // Define brake      (EDP: GPIO0)
DigitalOut Direction(p24);                  // Define direction  (EDP: EVG1_GPIO42)
DigitalOut L1(LED1);                        // User LEDs form bargraph
DigitalOut L2(LED2);
DigitalOut L3(LED3);
DigitalOut L4(LED4);

const int addr = 0xE0;                      // I2C device address for SRF08
char cmd[2];
char echo[3];
// echo[0] = light level
// echo[1] = MSB echo
// echo[2] = LSB echo
float temp8;
float range;  
float MotorPWM;

int main() {

// Set up SRF08 max range and receiver sensitivity
cmd[0] = 0x02;                          // Range register
cmd[1] = 0x1C;                          // Set max range about 100cm
sonar.write(addr, cmd, 2);
cmd[0] = 0x01;                          // Receiver gain register
cmd[1] = 0x1B;                          // Set max receiver gain
sonar.write(addr, cmd, 2);

// Set up PWM and motor control
motor.period(0.00005);                  // Set PWM frequency = 20kHz
motor.write(1);                         // Motor speed = 0
Brake = 0;                              // Brake on = 1, Brake off = 0
Direction = 0;

printf("\n\n\rCollision Avoidance Program Vsn 1.2\n\r");
printf("\n\r Range   Light\n\r");

while (1) {

// Get range data and light level from SRF08
// Send Tx burst command over I2C bus
cmd[0] = 0x00;                      // Command register
cmd[1] = 0x51;                      // Ranging results in cm
sonar.write(addr, cmd, 2);          // Send ranging burst

wait(0.07);

// Read back light level and range over I2C bus
cmd[0] = 0x01;                      // Address of light level
sonar.write(addr, cmd, 1, 1);       // Send address of light level      
sonar.read(addr, echo, 3);          // read light and echo result

// Generate PWM mark/space ratio from range data
range = (echo[1]<<8)+echo[2];
MotorPWM = range/100;               // Turn range into PWM ratio
if (temp8 != 0) {
motor.write(1-MotorPWM);         // Update PWM ratio (0 -> 1.0)
}
else {
motor.write(1);                  // PWM ratio = 0
}
pc.printf("  %3.0f", range);
pc.printf("     %3d\r", echo[0]);

// Keyboard input to toggle start/stop motor
if (pc.readable()) {                // Check for keyboard input
pc.getc();                       // Key pressed, clear buffer
if (temp8 == 0) {                // Motor already stopped?
Brake = 0;                    // Brake off, start motor
temp8 = range;
}
else {                           // Motor running
Brake = 1;                    // Brake on, stop motor
temp8 = 0;
}
}
wait(0.1);                          // Wait for 100ms

// Bargraph with mbed user LEDs
if (range > 70) {
L1 = 1, L2 = 1, L3 = 1, L4 = 1;
}
else if (range > 40) {
L1 = 1, L2 = 1, L3 = 1, L4 = 0;
}
else if (range > 25) {
L1 = 1, L2 = 1, L3 = 0, L4 = 0;
}
else if (range > 7) {
L1 = 1, L2 = 0, L3 = 0, L4 = 0;
}
else {
L1 = 0, L2 = 0, L3 = 0, L4 = 0;
}
}
}

0 comments

You need to log in to post a comment