I2C sample code for Devantech SRF08/SRF10 UltraSonic Ranger

[roboard]

Some people asked us how to interfacing with SRF08/SRF10 UltraSonic Ranger by RoBoard. This is easy using RoBoIO library; the following is a brief sample code.

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#include <stdio.h>
#include <conio.h>

#include <roboard.h>

//you need to change this function for Linux and DOS
void wait_ms(unsigned long ms) {
    unsigned long nowtime = GetTickCount();
    while ((GetTickCount() - nowtime) <= ms);
}

int main(void) {
    unsigned b1, b2;

    if (i2c_Initialize(I2CIRQ_DISABLE) == false)
    {
        printf("fail to initialize I2C (%s)!\n", roboio_GetErrMsg());
        return -1;
    }

    printf("set I2C speed to 400Kbps\n\n");
    i2c0_SetSpeed(I2CMODE_STANDARD, 400000L);

    do
    {
        printf("send SRF ranging command\n");

        //START with address 0xe0>>1 to write 2 bytes
        i2c0master_StartN(0xe0>>1, I2C_WRITE, 2);

        //Note: the SRF device address 0xe0 actually contains the I2C r/w bit,
        //      so we divide it by 2 to get the correct I2C slave address;
        //      see the I2C lib section of RoBoard SW intro. slide for more details.

        i2c0master_WriteN(0);       //set SRF command register
        i2c0master_WriteN(81);      //set ranging Mode - result in cm

        wait_ms(100); //wait 100ms

        printf("read SRF ranging data......\n");

        //START with address 0xe0>>1 to write 1 bytes
        i2c0master_StartN(0xe0>>1, I2C_WRITE, 1);

        //set RESTART to read 2 bytes after I2C writing
        i2c0master_SetRestartN(I2C_READ, 2);

        i2c0master_WriteN(2);       //set 1st SRF range register
        b1 = i2c0master_ReadN();    //read echo high byte
        b2 = i2c0master_ReadN();    //read echo low byte

        printf("result = %u\n\n", b1*256 + b2);

    } while (getch() != 27); //press ESC to quit

    i2c_Close();
    return 0;
}


The above sample code is for WinXP and WinCE; if you want to compile it at Linux or DOS, just change the wait_ms() function.

Note: in our test, SRF08/SRF10 can connect to RoBoard's I2C0_SCL, I2C0_SDA pins without pull-up resistors and run on 400Kbps. But for other I2C sensors, pull-up resistors may be necessary for fast I2C transmission (>100Kbps).

[roboard]

An additional remark: The old RoBoIO library v1.5b has a bug in I2C lib. To run the above sample correctly, you need to download the fix version of RoBoIO library v1.5b from the RoBoard website.

[Tsai Sung Yang]

Hi, I was trying to set up two SRF10, so I need to change one's address which default is 0xE0.

I tried above code and added this:

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i2c0master_StartN(0xe0>>1, I2C_WRITE, 5);
i2c0master_WriteN(0);     // Command
i2c0master_WriteN(0xA0);  // 1st in sequence to change I2C address
i2c0master_WriteN(0xAA);  // 2st in sequence to change I2C address
i2c0master_WriteN(0xA5);  // 3st in sequence to change I2C address
i2c0master_WriteN(0xE2);  // New address


but seems doesn't work, its address is still 0xE0

[roboard]

You can try to send each command to register at location 0 like following code:

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  i2c0master_StartN(0xE0>>1, I2C_WRITE, 2);
  i2c0master_WriteN(0);
  i2c0master_WriteN(0xA0);// 1st in sequence to change I2C address
  i2c0master_StartN(0xE0>>1, I2C_WRITE, 2);
  i2c0master_WriteN(0);
  i2c0master_WriteN(0xAA);// 2st in sequence to change I2C address

last to 0xE2

Reference:SRF10 Ultra sonic range finder
http://www.robot-electronics.co.uk/htm/srf10tech.htm

[Tsai Sung Yang]

It works!! Thank you!
So the function can only write 2 byte at a time?

You can try to send each command to register at location 0 like following code:

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  i2c0master_StartN(0xE0>>1, I2C_WRITE, 2);
  i2c0master_WriteN(0);
  i2c0master_WriteN(0xA0);// 1st in sequence to change I2C address
  i2c0master_StartN(0xE0>>1, I2C_WRITE, 2);
  i2c0master_WriteN(0);
  i2c0master_WriteN(0xAA);// 2st in sequence to change I2C address

last to 0xE2

Reference:SRF10 Ultra sonic range finder
http://www.robot-electronics.co.uk/htm/srf10tech.htm

[roboard]

According to the provisions of the SRF10,you can change address by only one method:
Send commands in the correct sequence to the command register at location 0, which means 4 separate write transactions on the I2C bus.

[Chaosmann]

Hi, have got a brand new SRF08 yesterday so I wanted to test it with the code above.
But after hours I found out that the first i2c0master_StartN call in the loop have to write to 0xE1 instead on 0xE0.

I've just written an example for Linux which reads the value from the light sensor:

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#include <iostream>
#include <stdio>                               // for in-/output
#include <unistd>                             // for usleep
#include "include/roboard.h"

#define SRF08Address 0xE0

using namespace std;

void GotoXY( int x, int y ) {
    printf("%c[%d;%df",0x1B,y,x);
}

void SRFStart( int add ) {
    i2c0master_StartN( add>>1, I2C_WRITE, 2 );
    i2c0master_WriteN( 0 );
    i2c0master_WriteN( 0x51 );
}

unsigned SRFReadLight( int add ) {
    //START with address 0xe0>>1 to write 1 bytes
    i2c0master_StartN( (add+1)>>1, I2C_WRITE, 1 );
    //set RESTART to read 2 bytes after I2C writing
    i2c0master_SetRestartN( I2C_READ, 1 );
    i2c0master_WriteN( 1 );
    return i2c0master_ReadN();
}

int main( void ) {
    unsigned b1, b2;

    printf( "\f" ); // clear the screen

    if (i2c_Initialize(I2CIRQ_DISABLE) == false) {
        printf("fail to initialize I2C (%s)!", roboio_GetErrMsg());
        return -1;
    }

    printf( "set I2C speed to 400Kbps" );
    i2c0_SetSpeed( I2CMODE_AUTO, 400000 );
    do {
        SRFStart( SRF08Address );
        usleep( 200000 );
        GotoXY( 1,2 ); cout << SRFReadLight( SRF08Address ) << "  " << endl;;
    } while ( true );

    i2c_Close();
    return 0;
}