ADXL345 - Arduino I2C library

C++ library for ADXL345 accelerometer for I2C communication with Arduino Wire library. Main features:

• read raw data (with offset and gain correction),
• low pass filtering for raw data,
• read scaled data,
• read normalized data,
• read events (free fall, single tap, double tap),
• accelerometer calibration process,
• device registers setting,
• communication sniff.

The library is intended to work without any user interference, just open project and upload working example and use it. However, if there is such a need, the user has the possibility of advanced configuration and use of the library.

Library uses I2C Interface, I2C Sensor Interface to simplify and unify working with I2C devices. The library also uses Status Class which is optional.

Getting Started

The working example for this library is writen in Atmel Studio 7 with Visual Micro addon. But it is possible to run it with Arduino IDE by adding files to project (probably there will be need to change the #include paths).

Prerequisites

• Software:
  • Atmel Studio 7 (tested) or Visual Studio,
  • Visual Micro addon for above AS7 or VS.
• Hardware:
  • Arduino Due (tested) or Arduino Uno (any ATmega 328P) board,
  • ADXL345 board or any IMU sensor with ADXL345.

Wiring

ADXL345 board	Due board	Uno board
SCL	SCL (21)	SCL (A4)
SDA	SDA (20)	SDA (A5)
VCC 3.3V*	3.3V	3.3V
VCC 5V*	- **	5V
GND	GND	GND

*If your ADXL345 board uses 5V or 3.3V and your MCU work on the similar voltage level (Due - 3.3V, Uno - 5V) this library provide you the possibility of restarting ADXL345 IC, see Calibration process below.

**The Due MCU cannot be exposed to the voltage above 3.3V level!

Example

To see a real-life example open AS7 project file ADXL345_Project.atsln and upload it (ADXL345_Project.ino) to a micro-controller. You should see something like that on Serial Monitor (baud rate = 115200):

2	Serial initialized with baud rate = 115200
104	Found ADXL345 searching device with ID = 0x53
105	AccX = 0.50	AccY = 0.00	AccZ = 10.57	m/s^2	pitch = -2.70	roll = 0.00
115	AccX = 0.42	AccY = -0.04	AccZ = 9.96	m/s^2	pitch = -2.42	roll = -0.22
...

Getting events

To see events {free fall, single tap, double tap} change defines in ADXL345_Project.ino file to:

#define PRINT_DATA 0x00 // 0x01 = Enable; Other = Disable
#define PRINT_EVENTS 0x01 // 0x01 = Enable; Other = Disable

Data rate and range setting

To change above in ADXL345_Project.ino file uncomment and choose appropriate in below:

// Set your Data Rate and Range or use defaults from ADXL345::init()
//		Accelerometer.setDataRate(->your_setting<-);
//		Accelerometer.setRange(->your_setting<-);

Advanced usage

As it was mentioned, the user has access to advanced options.

Calibration process

Due to manufacturing process, accelerometers have some problems with the data quality. In other words, to get the best accuracy, you need to calibrate it. In order to enable calibration in ADXL345.cpp file change ADXL345_ENABLE_CALIBRATION_PROCESS define to 0x01:

#define ADXL345_ENABLE_CALIBRATION_PROCESS 0x01

You should see something like that on Serial Monitor (baudrate = 115200):

2	Serial initialized with baudrate = 115200
104	Put acc pointing X axis up!
104	And then press key for example '3' when ready and press Enter.
104	... Or Press '1' key and Enter to finish! and get compensation parameters

Then follow the instructions from Serial Monitor. Important: be sure that you are able to type specific key in Serial Monitor.

Device restarting

Sometimes there is a problem with initialization (getting device ID, basically any information from the chip). This will be revealed by this:

354 I repeat the initialization of ADXL345 for the: 0 time
701 I repeat the initialization of ADXL345 for the: 1 time
...

There are to ways to fix it:

1. unplug and plug the device (USB cable) from power,
2. use the library.

The ADXL345 class constructor accepts as one of the arguments the deviceVCCPin. Instead of connecting the device VCC pin to 3.3V or 5V, it can be connected to one of the output pins. Then in case of initialization error, the library will be setting power on/off trying to restart the device. To change that pin in Config.h file, set ADXL345_VCC_PIN define to appropriate:

#define ADXL345_VCC_PIN 52

Important: in case of using modules like GY-80 (with multiple sensors) be sure that ADXL345 object is initializing as the first one. Otherwise, your program may behave unpredictably - many IC chips has volatile memory!

Single tap, double tap, free fall events detection

The IC provide many configurable registers (library sets default working values) for events detection, see functions:

ADXL345::setFreeFall();
ADXL345::setSingleTap();
ADXL345::setDoubleTap();

and for more see ADXL345 datasheet.