adxl345 | adxl345 full function driver for general microcontroller

The first thing which confuses me is where I have to write the data to set resolution for +/-2g. I didn't find any mention of this register in the datasheet.

You'll find this information on page 26 of the data sheet (at least, in Rev. E of the data sheet). The range is controlled by bits 0 and 1 in register 0x31 (DATA_FORMAT).

Register 0x31—DATA_FORMAT (Read/Write)

The DATA_FORMAT register controls the presentation of data to Register 0x32 through Register 0x37. All data, except that for the ±16 g range, must be clipped to avoid rollover.

SELF_TEST Bit

A setting of 1 in the SELF_TEST bit applies a self-test force to the sensor, causing a shift in the output data. A value of 0 disables the self-test force.

SPI Bit

A value of 1 in the SPI bit sets the device to 3-wire SPI mode, and a value of 0 sets the device to 4-wire SPI mode.

INT_INVERT Bit

A value of 0 in the INT_INVERT bit sets the interrupts to active high, and a value of 1 sets the interrupts to active low. FULL_RES Bit

When this bit is set to a value of 1, the device is in full resolution mode, where the output resolution increases with the g range set by the range bits to maintain a 4 mg/LSB scale factor. When the FULL_RES bit is set to 0, the device is in 10-bit mode, and the range bits determine the maximum g range and scale factor.

Justify Bit

A setting of 1 in the justify bit selects left-justified (MSB) mode, and a setting of 0 selects right-justified mode with sign extension.

Range Bits

These bits set the g range as described in Table 21.

Table 21. g Range Setting

Your math seems to be a bit off; for this accelerometer (from the datasheet: https://www.sparkfun.com/datasheets/Sensors/Accelerometer/ADXL345.pdf), in order to read the 6 bytes of XYZ sample data, you need to perform a 6-byte burst read of the registers. What this means in terms of data transfer is a write of the register address to the accelerometer (0x31) then a burst read of 6 bytes continuously. Each of these two transfers requires sending first the I2C device address and the R/W bit, as well as an ACK/NAK per byte, including the address bytes, as well as START/REPEAT START/STOP conditions. So, over all, an individual transfer to get a single sample (ie, a single XYZ acceleration vector) is as follows:

Let's take a step back and think about what this block of code is doing:

You have opened the file in "wb" mode for writing.

file = open('/var/log/sensor/' + active_file_first, 'wb')

So it is expecting the data to be written in the file to be byte objects.

You need to convert the string you are writing into byte object or maybe change the mode in which you opened the file to "w" mode.

file = open('/var/log/sensor/' + active_file_first, 'w')

Just unpack them using * operator:

The ADXL345 data sheet says the fastest sampling rate using fast i2c is 800Hz. SPI is needed to get faster sampling rates--up to 3200Hz.

It looks like the Adafruit_ADXL345 library only supports i2c. And it's deprecated. The Adafruit Blinka library supports SPI, but you'll have to roll your own ADXL345 interface.

I suspect from the Sparkfun board notes (https://www.sparkfun.com/products/14812) that the problem is that the Redboard Turbo is a 32-bit processor, with a 32-bit int instead of a 16-bit int. On such a processor, all 16 bit values stored in an int are positive.

To test my theory, run the following Sketch on your Redboard Turbo:

The Error: port in use error indicates you already have a process using port 1880.

It is likely you already have Node-RED running on your BeagleBoneBlack. You can check this by running:

Your WriteRegister and ReadRegister functions do not follow the flowcharts defined in the TM4C123G data sheet. Apart from not checking or handling the MCS ERROR flag, Figure 16-10 Master TRANSMIT of Multiple Data Bytes shows that when writing the MCS register, you should assert specific bits, while you are writing to all bits, You should instead perform a read-modify-write: