I2C accellerometer - Revision history

Cartridge1987 at 11:09, 11 November 2015

2015-11-11T11:09:31Z

Rew: /* general info */

2015-08-11T14:27:02Z

general info

Rew: Created page with "= general info = The I2C accellerometer is based on the MMA8652. = pinout = As with all bitwizard I2C boards, the board has a 4 pin female connector on the left and a male ..."

2015-08-11T11:35:08Z

Created page with "= general info = The I2C accellerometer is based on the MMA8652. = pinout = As with all bitwizard I2C boards, the board has a 4 pin female connector on the left and a male ..."

New page

= general info =

The I2C accellerometer is based on the MMA8652.

= pinout =

As with all bitwizard I2C boards, the board has a 4 pin female connector on the left and a male connector on the right so that you can daisychain multiple boards.

The pinout is GND, SDA, SCL, VCC.

== voltages ==

The chip is 3.3V, a regulator is provided on board. This regulator has a dropout of about 1V, so the board currently requires a 5V VCC. We'll move to a different regulator one of these days allowing clean 3.3V operation. (the dropout will be so low that the chip will have to make do with 3.299V if you provide 3.300V....)

= examples =

This is a sample script that runs on raspberry pi to extract the X, Y and Z accellerometer values. It requires you install the bw_tool.

#!/bin/sh
acc="bw_tool -I -D /dev/i2c-1 -a 3a"
# reset the accelerometer.
$acc -W 2b:40:b
# minimum 1ms IIRC.
sleep 0.01
#
#select range=1 for +/- 4G fs range.
#range=1
range=0
#
$acc -W 0e:"$range":b 2b:2:b 2c:0:b 2d:1:b 2e:1:b 2a:39:b
sleep 1
#$acc -R 0:l
result=`$acc -R 0:l |sed -e 's/$..$/\1 /g' `
#echo $result
x=`echo $result | awk '{print $7$6}'`
y=`echo $result | awk '{print $5$4}'`
z=`echo $result | awk '{print $3$2}'`
echo x=$x y=$y z=$z

The numbers are presented in hex. Remember that (in the default +/-2G fs range) 4000 is one G, c000 is about minus one G.

Mine currently reports:
x=0c70 y=0580 z=3f30
so it is not quite flat (X and Y significantly differ from zero. I get about +/- 60 when its pressed to the table). but it is still registering almost a full G in the Z direction .

= datasheets =

[[http://cache.freescale.com/files/sensors/doc/data_sheet/MMA8652FC.pdf]]

@@ Line 1: / Line 1: @@
-= general info =
+= General info =
 The I2C accellerometer is based on the MMA8652 from freescale.
-= pinout =
+= Pinout =
 As with all bitwizard I2C boards, the board has a 4 pin female connector on the left and a male connector on the right so that you can daisychain multiple boards.
@@ Line 9: / Line 9: @@
 The pinout is GND, SDA, SCL, VCC.
-== voltages ==
+== Voltages ==
 The chip is 3.3V, a regulator is provided on board. This regulator has a dropout of about 1V, so the board currently requires a 5V VCC. We'll move to a different regulator one of these days allowing clean 3.3V operation. (the dropout will be so low that the chip will have to make do with 3.299V if you provide 3.300V....)
-= examples =
+= Examples =
 This is a sample script that runs on raspberry pi to extract the X, Y and Z accellerometer values. It requires you install the bw_tool.
@@ Line 45: / Line 45: @@
-= datasheets =
+= Datasheets =
 [[http://cache.freescale.com/files/sensors/doc/data_sheet/MMA8652FC.pdf]]