Am totally new to electronics and the datasheet is very confusing to me, so can anyone please guide me through the specification of the accelerometer? So that i can have a better understanding on the accelerometer and to be able to convert the accelerometer data into G.

X-axis Y-axis Z-axis -28 -26 218 These are the readings i get from the accelerometer with a +-2g range

This is the datasheet for the ADXL345 digital accelerometer [1]: https://www.analog.com/media/en/technical-documentation/data-sheets/ADXL345.pdf

 

Hi ckkk,
Welcome to AAC,
Have you checked this link.?
https://learn.adafruit.com/adxl345-digital-accelerometer/programming
E

 

Hi ckkk,
Welcome to AAC,
Have you checked this link.?
https://learn.adafruit.com/adxl345-digital-accelerometer/programming
E

I did, but there isn't any explanation on how to convert from raw data to g.

 

Source: Datasheet
The ADXL345 is a small, thin, ultralow power, 3-axis accelerometer with high resolution (13-bit) measurement at up to ±16 g. Digital output data is formatted as 16-bit twos complement and is accessible through either a SPI (3- or 4-wire) or I2C digital interface. The ADXL345 is well suited for mobile device applications. It measures the static acceleration of gravity in tilt-sensing applications, as well as dynamic acceleration resulting from motion or shock. Its high resolution (3.9 mg/LSB) enables measurement of inclination changes less than 1.0°.

That device, like others with which I am familiar, reports directly in g . If you want angle or to correct for other than the stationary state, then you need to use trig or an approximation.

 

That device, like others with which I am familiar, reports directly in g . If you want angle or to correct for other than the stationary state, then you need to use trig or an approximation.

If it is already in g wouldn't the z-axis output close to 1? As i did some research and found out that when the sensor is stationary the z-axis should have a 1g output.

 

On the datasheet, "Full resolution, where resolution increases with g range, up to 13-bit resolution at ±16 g (maintaining 4 mg/LSB scale factor in all g ranges)"
Which makes 0,004 g per bit. Your 218 would be 218*0,004 g = 0,872 g.

 

On the datasheet, "Full resolution, where resolution increases with g range, up to 13-bit resolution at ±16 g (maintaining 4 mg/LSB scale factor in all g ranges)"
Which makes 0,004 g per bit. Your 218 would be 218*0,004 g = 0,872 g.

Which means no matter what measurement range the accelerometer is on the output data should always multiply by 0.004g?

 

I have not used ADXL345, but there seems to be different (user select-able) output resolutions that affects to scaling. Output resolution and sensitivity is on the table 1 in datasheet page 5. For example for +-4 g range, resolution can be 10 bits or 11 bits. 11 bits is full resolution. With 10 bit resolution scaling is 7,8 mg/LSB and with full resolution scaling is 3,9 mg/LSB. On a quick look, resolution is set with Register 0x31—DATA_FORMAT (Read/Write).

 

I have not used ADXL345, but there seems to be different (user select-able) output resolutions that affects to scaling. Output resolution and sensitivity is on the table 1 in datasheet page 5. For example for +-4 g range, resolution can be 10 bits or 11 bits. 11 bits is full resolution. With 10 bit resolution scaling is 7,8 mg/LSB and with full resolution scaling is 3,9 mg/LSB. On a quick look, resolution is set with Register 0x31—DATA_FORMAT (Read/Write).

Wait i don't understand, i thought with +-4g range it will be 11bits? Also why with 10bit resolution scaling is 7.8mg/lsb and with full resolution the scaling is 3.9 mg/lsb?