This is a C driver program for operating a Memsic MMC33416xPJ magnetic sensor via I2C on a Raspberry Pi. I used it with the Digilent CMPS2 PMOD module, connected to the PMOD4 port of the PMOD2RPI board on a Raspberry Pi 4. On a standard Pi, the I2C bus already has 1k8 pull-ups to 3V3 and the module's pull-up jumpers are kept open.
For I2C communication functions, I am using the i2c-tools and i2c-dev packages.
sudo apt-get install -y i2c-tools libi2c-dev
Now we can use the i2cdetect command to query the I2C bus. The Memsic MMC3416xPJ sensor address is factory-hardcoded from 0x30 to 0x38. The address is part of the ordering type name: MMC34160PJ = 0x30, MMC34161PJ = 0x31, and so forth. The Digilent CMPS2 PMOD module uses MMC34160PJ at address 0x30:
root@pi-ws01:/home/pi# i2cdetect -y 1
0 1 2 3 4 5 6 7 8 9 a b c d e f
00: -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: 30 -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
...
70: -- -- -- -- -- -- -- --
Compiling the test program:
pi@pi-ms05:~/pmod2rpi/pi-mmc3416 $ make
gcc -O3 -Wall -g -c -o i2c_mmc3416.o i2c_mmc3416.c
gcc -O3 -Wall -g -c -o getmmc3416.o getmmc3416.c
gcc i2c_mmc3416.o getmmc3416.o -o getmmc3416 -lm
Extracting the sensor product ID and configuration information with "-i":
pi@pi-ms05:~/pmod2rpi/pi-mmc3416 $ ./getmmc3416 -i
----------------------------------------------
MMC3416 Information Sat Oct 23 12:36:15 2021
----------------------------------------------
Sensor Product ID = 0x06 MEMSIC MMC3416xPJ
Continuous Read State = 0x00 Disabled
Continuous Read Freq. = 0x00 1.5 Hz (1 sample every 1.5 seconds)
No Boost CAP charging = 0x00 CAP charge pump enabled
Output Resolution = 0x01 16 bit (4.08ms read time)
Taking a single measurement, using the "-t" argument
pi@pi-ms05:~/pmod2rpi/pi-mmc3416 $ ./getmmc3416 -t
1634960403 Heading=326.0 degrees
Program usage:
pi@pi-ms05:~/pmod2rpi/pi-mmc3416 $ ./getmmc3416
Usage: getmmc3416 [-b i2c-bus] [-c 0..3] [-d] [-i] [-l decl] [-m mode] [-t] [-r] [-o htmlfile] [-v]
Command line parameters have the following format:
-b I2C bus to query, Example: -b /dev/i2c-1 (default)
-c start continuous read with a given frequency 0..3. examples:
-c 0 = read at 1.5 Hz (1 sample every 1.5 seconds - default)
-c 1 = read at 13 Hz (1 sample every 77 milliseconds)
-c 2 = read at 25 Hz (1 sample every 40 milliseconds)
-c 3 = read at 50 Hz (1 sample every 20 milliseconds)
-d dump the complete sensor register map content
-i print sensor information
-l local declination offset value (requires -t/-c), example: -l 7.73
see http://www.ngdc.noaa.gov/geomag-web/#declination
-m set sensor output resolution mode. arguments: 12/14/16/16h. examples:
-m 12 = output resolution 12 bit (1.20ms read time)
-m 14 = output resolution 14 bit (2.16ms read time)
-m 16 = output resolution 16 bit (4.08ms read time)
-m 16h = output resolution 16 bit (7.92ms read time)
-r reset sensor
-t take a single measurement
-o output data to HTML table file (requires -t/-c), example: -o ./mmc3416.html
-h display this message
-v enable debug output
Usage examples:
./getmmc3416 -b /dev/i2c-0 -i
./getmmc3416 -t -v
./getmmc3416 -c 1
./getmmc3416 -t -l 7.73 -o ./mmc3416.html
The sensor register data can be dumped out with the "-d" argument:
pi@pi-ms05:~/pmod2rpi/pi-mmc3416 $ ./getmmc3416 -d
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MEMSIC MMC3416xPJ register dump:
------------------------------------------------------
reg 0 1 2 3 4 5 6 7 8 9 A B C D E F
------------------------------------------------------
[0x00] B4 7E 87 7E 1F 82 05 61 61 -- -- -- -- -- -- --
[0x10] -- -- -- -- -- -- -- -- -- -- -- 00 00 00 00 00
[0x20] 06
Sensor Reg: hex binary
---------------------------
Xout Low: 0xB4 0b10110100
Xout High: 0x7E 0b01111110
Yout Low: 0x87 0b10000111
Yout High: 0x7E 0b01111110
Zout Low: 0x1F 0b00011111
Zout High: 0x82 0b10000010
Status: 0x05 0b00000101
Control-0: 0x61 0b01100001
Control-1: 0x61 0b01100001