Month: December 2014

MMA88451 doesn’t work with raspbterry pi out of the box. It needs I2C with repeated start. Test program in python:

import smbus
DEVICE_ADDRESS = 0x1d
MMA8451_REG_WHOAMI = 0x0D
bus = smbus.SMBus(1)
ret = bus.read_byte_data(DEVICE_ADDRESS, MMA8451_REG_WHOAMI)
print ret

Shows zero instead of expected 26 (0x1A in hex)

pi@occberry ~/OpenCyclingComputer $ sudo python src/mma8451.py
0

Solution that I found here solves the problem:

sudo chmod 666 /sys/module/i2c_bcm2708/parameters/combined
sudo echo -n 1 > /sys/module/i2c_bcm2708/parameters/combined

and now the python test code shows, as expected:

pi@occberry ~/OpenCyclingComputer $ sudo python src/mma8451.py
26

[1] www.adafruit.com/products/2019

[2] www.raspberrypi.org/forums/viewtopic.php?f=44&t=15840&start=25

https://gitlab.com/PrzemoF/mtk3339

Python library for Raspberry PI for Ultimate GPS based on MTK3339 with serial interface as sold by Adafruit. The library helps to set different chip parameters in a sane way. Currently supports minimum functional set of commands:

CMD_HOT_START – hot_start()

CMD_WARM_START – warm_start()

CMD_COLD_START – cold_start()

CMD_FULL_COLD_START – cold_reset()

SET_NMEA_UPDATERATE – set_nmea_update_rate()

SET_NMEA_BAUDRATE – set_baudrate()

API_SET_FIX_CTL – set_fix_update_rate()

API_SET_NMEA_OUTPUT – set_nmea_output()

SET_NAV_SPEED_TRESHOLD – set_nav_speed_threshold()

All functions are preforming basic range check to make sure values are accepted by MTK3339 as there is no check if a call was successful or not.

Example usage:

import mkt3339

gps = mt3339(“/dev/ttyAMA0”)

gps.set_fix_update_rate(800)

gps.set_nmea_update_rate(800)

gps.set_baudrate(115200)

gps.set_nmea_update_rate(1000)

gps.set_nav_speed_threshold(1.5)

gps.set_nmea_output(gll = 0, rmc = 1, vtg = 0, gga = 5, gsa = 5, gsv = 5)

That library is part of Open Cycling Computer project