Brent Dekker / SRF08

Library for interfacing the SRF08 ultrasonic range sensor. Most functions of the SRF08 are covered, including interrupt-based waiting for the ranging process to finish

Dependents:   DISCO-F746NG_LCDTS_demo Srf08Test

/media/uploads/brentdekker/ultrasonic-range-finder-srf08.jpg

SRF08

Warning

Don't forget to add the pullup resistors from 5v to SDA and SCL!

Information on the SRF08 can be found here: http://www.robot-electronics.co.uk/htm/srf08tech.shtml

Example program

#include "mbed.h"
#include "SRF08.h"

Serial PC(USBTX, USBRX);       //Debug port to PC
SRF08 rangeMod1(p28, p27, 0xE4); //SRF08 ranging module 1
SRF08 rangeMod2(p28, p27, 0xE2); //SRF08 ranging module 2

int main() {
    PC.printf("Start ranging test \n");
    rangeMod1.setAddress(0xE4); //Factory default is 0xE0
    while(1) {
        rangeMod1.startRanging();
        while (!rangeMod1.rangingFinished() ) wait(0.01);
        int range1 = rangeMod1.getRange();
        int light1 = rangeMod1.getLightIntensity();
        rangeMod2.startRanging();
        while (!rangeMod2.rangingFinished() ) wait(0.01);
        int range2 = rangeMod2.getRange();
        PC.printf(" Range_1: %i", range1);
        PC.printf(" Range_2: %i", range2);
        PC.printf(" Light_1: %i", light1);
        PC.printf("\n");
    }
}

Library

Import library
SRF08 - SRF08 Class Reference

Public Member Functions

SRF08 (PinName SDA, PinName SCL, int i2cAddress)
Create a SRF08 object connected to the specified I2C pins and address.
void startRanging ()
Send the "Start ranging in cm" command via I2C.
bool rangingFinished ()
Checks if the module has finished ranging.
int getRange ()
Gets the measured range from the module.
int getLightIntensity ()
Gets the measured light intensity from the module.
void setRangeRegister (unsigned char rangeVal)
Sets the range register of the SRF08 for faster ranging.
void setMaxGainRegister (unsigned char gainVal)
Sets the max gain register of the SRF08 .
void setAddress (int i2cAddress)
Changes the I2C address of the SRF08 .

Diff: SRF08.cpp

Revision:
1:76fb116fa28d
Parent:
0:4e0a8193b92e
Child:
2:ca82f89f415d
--- a/SRF08.cpp	Thu Jul 05 09:53:18 2012 +0000
+++ b/SRF08.cpp	Tue Jul 10 08:48:02 2012 +0000
@@ -31,7 +31,8 @@
  * Returns:     void
  * Description: Creates an instance of the SRF08 to communicate with a sRF08 module
  */
-SRF08::SRF08(PinName sda, PinName scl, int addr) : m_i2c(sda, scl), m_addr(addr) {
+SRF08::SRF08(PinName sda, PinName scl, int addr) :
+        m_i2c(sda, scl), m_addr(addr), rangeBuf(), rangeBufIndex(0) {
     char cmd[2];
     // Set up SRF08 max range and receiver sensitivity over I2C bus
     cmd[0] = 0x02;                          // Range register
@@ -53,12 +54,58 @@
 }
 
 /*
+ * Function:    startRanging
+ * Args:        void
+ * Returns:     void
+ * Description: Sends command to module to start ranging.
+ */
+void startRanging() {
+    // Send Tx burst command over I2C bus
+    cmd[0] = 0x00;                      // Command register
+    cmd[1] = 0x51;                      // Ranging results in cm
+    m_i2c.write(m_addr, cmd, 2);        // Send ranging burst
+}
+
+/*
+ * Function:    rangingFinished
+ * Args:        void
+ * Returns:     Bool: whether ranging is finished
+ * Description: Checks if the ranging process on the module is finished
+ */
+bool rangingFinished() {
+    char cmd = 0x00; //Software revision register
+    char echo;
+    m_i2c.write(m_addr, cmd, 1, 1); //Send address of software rev register
+    m_i2c.read(m_addr, echo, 1);    //Read 1 byte echo result
+    if (echo == 0xFF) return false;
+    return true;
+}
+
+/*
+ * Function:    getRange
+ * Args:        void
+ * Returns:     int range
+ * Description: Range in cm. This function should only be called when ranging is finished, otherwise previous value is returned
+ */
+void getRange() {
+    char cmd[2];
+    char echo[2];
+    // Read range over I2C bus
+    cmd[0] = 0x02;                      // Address of first echo
+    m_i2c.write(m_addr, cmd, 1, 1);     // Send address of first echo
+    m_i2c.read(m_addr, echo, 2);        // Read two-byte echo result
+    // Generate PWM mark/space ratio from range data
+    int range = (echo[0]<<8)+echo[1];
+    return range;
+}
+
+/*
  * Function:    readRange
  * Args:        void
  * Returns:     int range
  * Description: Reads the range register and converts it to a usable value
  */
-int SRF08::read() {
+int SRF08::readRange() {
     char cmd[2];
     char echo[2];
 
@@ -82,6 +129,24 @@
 }
 
 /*
+ * Function:    readBufRange
+ * Args:        void
+ * Returns:     int range
+ * Description: Reads the range register, adds it to an array and converts it to a filtered value
+ */
+//int SRF08::readBufRange() {
+
+//}
+
+int SRF08::getAverageBufRange() {
+    int total = 0;
+    for (int i = 0; i < RANGEBUFSIZE; i++) {
+        total += rangeBuf[i];
+    }
+    return (int)total/RANGEBUFSIZE;
+}
+
+/*
  * Function:    setRangeRegister
  * Args:        rangeVal
  * Returns:     void