Wii Motion plus Gyros on RaspberryPi

Here’s a really quick post about the Wii Motion Plus (again !) and how to make it work with the Raspberry Pi…

I’ve connected this nice little device to an Arduino (obviously ! 🙂 ), to a IOIO board, a FEZ Domino and even to an obscure TI Arm board, the LM3S8962 using CooCox… so it was only right that I connect it to my “new” Raspberry Pi board.

Connecting the Wii Motion Plus to the Raspberry Pi board

Before anything else, one has to enable I2C on the Raspberry Pi. There are plenty of articles on the Internet on how to do that, I’ll just remind here the main steps:

1. edit /etc/modprobe.d/raspi-blacklist.conf and UN-blacklist i2c-bcm2708
2. edit /etc/modules and add i2c-dev
3. install i2c-tools and python-smbus
4. add you user to the i2c group
5. connect the device and check that it’s visible with i2cdetect -y 1

And here is the Python script that reads the data and displays it every 100 milliseconds

#test connection to Wii Motion plus

import smbus
import time

bus = smbus.SMBus(1)	#the RaspberryPi B V2 has the bus #1 exposed on the pins 3/SDA and 5/SCL
ADDR_INIT = 0x53	#WM+ starts out deactivated at this address (can be seen by doing i2cdtect -y 1)
ADDR = 0x52


def initGyros():
	bus.write_byte_data(ADDR_INIT, 0xFE, 0x04)
	time.sleep(0.01)

def readGyros(gyroZeroes):
	bus.write_byte(ADDR, 0x00)	#send zero before each request
	#there are 6 bytes of data sent by the WM+	
	data0 = bus.read_byte(ADDR)
	data1 = bus.read_byte(ADDR)
	data2 = bus.read_byte(ADDR)
	data3 = bus.read_byte(ADDR)
	data4 = bus.read_byte(ADDR)
	data5 = bus.read_byte(ADDR)
	
	gyroZ = ((data3 >> 2) << 8) + data0 - gyroZeroes[2]
	gyroX = ((data4 >> 2) << 8) + data1 - gyroZeroes[0]
	gyroY = ((data5 >> 2) << 8) + data2 - gyroZeroes[1]
	
	return (gyroX, gyroY, gyroZ)


def calibrateGyrosZeroes():
	tempX = 0
	tempY = 0
	tempZ = 0
	gyroX0 = 0
	gyroY0 = 0
	gyroZ0 = 0

	for i in xrange(10):
		vals = readGyros((0, 0, 0))
		tempX += vals[0]
		tempY += vals[1]
		tempZ += vals[2]
	
	# average the 10 readings
	gyroX0 = tempX / 10
	gyroY0 = tempY / 10
	gyroZ0 = tempZ / 10
	
	return (gyroX0, gyroY0, gyroZ0)


#MAIN program / loop
try:
	initGyros()
except IOError:
	print "Couldn't INIT gyros, maybe they are already initialised..."

gyroZeroes = calibrateGyrosZeroes()
print "Calibrated: " + str(gyroZeroes)


while True:
	print readGyros(gyroZeroes)
	time.sleep(0.1)