Works fine with 3.3v.
Connections:
HMC5883L BBB
VCC P9 – 3
GND P9 – 2
SCL P9 – 17
SDA P9 – 18 //Sorry, Had a typo here, should be P9 - 18 not P9 - 19
Add “BB-I2C1” to uEnv.txt. So the first line looks like:
optargs=quiet drm.debug=7 capemgr.enable_partno=BB-UART1,BB-I2C1
(Note: the “BB-UART1” entry is from my Ultimate GPS example in this forum.)
The following is the C code. (gcc compass.c -o compass)
The contents of the 6 data registers are printed.
==============================================
Code: Select all
//compass.c for the HMC5883L
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <termios.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <linux/i2c-dev.h>
#include <stdlib.h>
#include <time.h>
/* change this definition for the correct port */
#define COMPASS "/dev/i2c-2" //I2C port
//NOTE: I think I am using i2c-1. I have connected the HMC5883L to pins 17,18 on P9.
//Hard to argue with i2ctools.
#define _POSIX_SOURCE 1 /* POSIX compliant source */
main()
{
int fd, c, res;
int daddr = 0x1e; //address of HMC5883L before shifting.
int i;
useconds_t dtime = 8; //delay for usleep
// buffers for commands.
char write0[4]; // command to set reg 0 - AKA Configuration Register A
char write1[4]; // command to set reg 1 - AKA Configuration Register B
char write2[4]; // command to set reg 2 - AKA Mode Register
write0[0] = 0x00; // reg 00
write0[1] = 0x70; // average 8 samples, 15Hz output
write1[0] = 0x01; // reg 01
write1[1] = 0xA0; // gain 5
write2[0] = 0x02; // reg 02
write2[1] = 0x01; // mode single measurement
//
char buf[10];
if ((fd = open(COMPASS, O_RDWR )) < 0) {;
perror("Failed to open the I2C bus\n");
exit(1);
}
// Sets the slave address for reads & writes
// see i2c-dev.h
if (ioctl(fd, I2C_SLAVE,daddr) < 0) {
printf("Failed to access\n");
exit(1);
}
//Set reg 0
if (write(fd,write0,2) != 2) {
printf("Write to zero failed\n");
}
//Set reg 1
if (write(fd,write1,2) != 2) {
printf("Write to one failed\n");
}
//Set reg 2
if (write(fd,write2,2) != 2) {
printf("Write to two failed\n");
}
//datasheet says to delay here.
if ( usleep(dtime) < 0) {
printf("sleep error\n");
}
//read the 6 data.
if (read(fd, buf, 6) != 6) {
printf("Read failed\n");
}
for (i = 0;i<6;i++) {
printf("values %d %x\n",i,buf[i]);
}
}
For some instruction in using the i2c-tools see: Beaglebone: An I2C Tutorial - Interfacing to a BMA180
by Derek Molloy
You can find the video on Youtube.
