last update 060306, by Guy Lee

The first thing needs to notice is that MMA7260Q operates on a 3.3V circuit.

You can check the detailed instruciton here, by Tom Igoe. However, I got a different schematic from Tom's. The one I used is showed as the image below, which comes from some other classmate's already-working circuit:

After connecting the serial port to PC, I could see three numbers which accordingly stand for hte data of X, Y and Z axis in serial communicator. Here I have a question: why is the initial data of MMA7260Q (131,124,186) instead of (0,0,0)? Is that because I didn't initialize the sensor? or something I missed?

Here presents the directions of three axes. However I find it's quite hard to trigger only one axis. I am still trying to figure out how the rotaion exactly changes the data. When I shake the sensor like the first picture below, for example, it seems that all three numbers, instead of only X value, get a big change.

Red wave stands for the change of X axis, green for Y and blue for Z. Circled parts meet the major change when I shake the sensor. (If the variation isn't obvious enough, you can adjust the Processing code and multiply the value by 2 or more)

[Processing code]

see here.

[PicBasic code]

DEFINE ADC_BITS 10 ' Set number of bits in result
DEFINE ADC_CLOCK 3 ' Set clock source (3=rc)
DEFINE ADC_SAMPLEUS 15 ' Set sampling time in uS

tx var portc.6
rx var portc.7
n9600 con 16468

adcVar VAR word[3] ' Create variable to store results
channel var byte
byteVar var byte[3]
inByte var byte

' set Sleep pin high:

' Set PORTA to all input
TRISA = %11111111

' Set up ADCON1:
' AN3 = VREF+, all other analog pins are set to analog.
' See PIC 18F452 datasheet for details:
ADCON1 = %10000010

' wait for a byte:
'serin2 rx, n9600, [inByte]

' read all channels of the accelerometer:
for channel = 0 to 2
ADCIN channel, adcVar[channel]
' convert to a byte:
byteVar[channel] = adcVar[channel] /4
pause 20

' send results out the serial port:
serout2 tx, n9600, [DEC byteVar[0],44,DEC byteVar[1],44,DEC byteVar[2],13,10]
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