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https://github.com/AlekseyFedorovich/ADXL345_spi_micropython

Library for interacting through the SPI protocol with an 'Analog Devices ADXL345' accelerometer from an MCU flashed with MicroPython. Methods are optimised for trying to reach max available sampling rate for this device
https://github.com/AlekseyFedorovich/ADXL345_spi_micropython

accelerometer adxl345 esp32 frequency micropython micropython-esp32 vibrational-analysis

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Library for interacting through the SPI protocol with an 'Analog Devices ADXL345' accelerometer from an MCU flashed with MicroPython. Methods are optimised for trying to reach max available sampling rate for this device

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README 

        
# uPy - ADXL345 - SPI

Library for controlling through the SPI protocol an 'Analog Devices ADXL345' accelerometer from an MCU flashed with MicroPython (in particular this was tested with a **ESP32-WROVER** (4MB RAM)).



Methods are optimised for being as fast as possible, trying to reach max available sampling rate (3.2kHz) for this device.



## Wiring

The following wirings refers to the tested setup on an ESP32-WROVER:



ADXL345 Pin name  | ESP32 Pin name (number)

 ---------------- | -----------------------

Vs                | 3v3

GND               | GND

CS                | vspi cs (D5)

SCL/SCLK          | vspi scl (D18)

SDO/ALT ADDRESS   | vspi miso (D19)

SDA/SDI/SDO       | vspi mosi (D23)



## RAM and MemoryErrors

Consider that at high sampling rates the MCU collects 3_axes x sampling_rate floats per second. This may result in ending the available RAM of MCUs very quickly: set your acquisition time accordingly and clear data arrays when you are done with them. 



## Examples

### read one x, y, z

``` python

from ADXL345_spi import ADXL345 as Accelerometer

accelerometer = Accelerometer(cs_pin=5, scl_pin=18, sda_pin=23, sdo_pin=19, spi_freq=5000000)

accelerometer.init_spi()

accelerometer.set_sampling_rate(1.56)   # Hz

accelerometer.set_g_range(2)            # max measurable acceleration pm 2g

accelerometer.set_fifo_mode('bypass')

accelerometer.set_power_mode('measure')

buf, T = accelerometer.read_many_xyz(n=1)

accelerometer.set_power_mode('standby')

x, y, z = accelerometer.xyzbytes2g(buf)  # convert bytearray in 3 acceleration arrays (x, y, z) in g units

accelerometer.deinit_spi()  # this is necessary, otherwise if another SPI is initialized it won't work

```



### read many x, y, z

``` python

from ADXL345_spi import ADXL345 as Accelerometer

accelerometer = Accelerometer()                     # assumes accelerometer is connected to MCU spi default Pins

accelerometer.init_spi()

accelerometer.set_sampling_rate(3200)

accelerometer.set_g_range(2)

accelerometer.set_fifo_mode('bypass')

accelerometer.set_power_mode('measure')

buf, T = accelerometer.read_many_xyz(n=10)  # reads ten samples for each axis at the requested sampling rate

accelerometer.set_power_mode('standby')

x, y, z = accelerometer.xyzbytes2g(buf)     # arrays of length 10, to be associated with the T array that holds the times of the measure of each sample

accelerometer.deinit_spi()

```



### read continuosly when data is ready

``` python

from ADXL345_spi import ADXL345 as Accelerometer

accelerometer = Accelerometer()

accelerometer.init_spi()

accelerometer.set_sampling_rate(3200)

accelerometer.set_g_range(2)

accelerometer.set_fifo_mode('bypass')

accelerometer.set_power_mode('measure')

buf, T = accelerometer.read_continuos_xyz(acquisition_time=1.5)  # reads samples for 1.5 seconds from each axis at the requested sampling rate

accelerometer.set_power_mode('standby')

x, y, z = accelerometer.xyzbytes2g(buf)  # arrays (in principle) of length acquisition_time * sampling_rate 

accelerometer.deinit_spi()

```



### read continuosly from fifo

The method for reading from fifo is implemented even though it doesn't read more than one row of the fifo in one transaction, making its performances equal to the method reading measures when they are ready. Trying to read more than one row of the fifo in one transaction always resulted in reading following registers instead of other rows of the fifo.

``` python

from ADXL345_spi import ADXL345 as Accelerometer

accelerometer = Accelerometer()

accelerometer.init_spi()

accelerometer.set_sampling_rate(3200)

accelerometer.set_g_range(2)

accelerometer.set_fifo_mode('stream')

accelerometer.set_power_mode('measure')

buf, T = accelerometer.read_continuos_xyz_fromfifo(acquisition_time=1.5)

accelerometer.set_power_mode('standby')

x, y, z = accelerometer.xyzbytes2g(buf)

accelerometer.deinit_spi()

```