Using nrf51822 board with adxl335 accelerometer (ADC)

[vitaminwater]

Hi,

I'm trying to use adxl335 accelerometer to detect motion.

I'm having trouble understanding what the output of the accelerometer means. Obviously, it should tell me something about the acceleration but it's in unit mV/g. How do I interpret this output and convert it into data related to acceleration or motion?

Also, I've found a lot of codes on adxl335 with Arduino, but there seems to be less resources on adxl335 with nrf51822 kit. I'm trying to use the GPIOs and program it to do the ADC conversion. Could anyone help me on this?

Thank you a lot.

[Clem Taylor]

Save yourself the pain and use a digital accelerometer with an I2C or SPI interface.

The nrf51 ADC is fairly slow, is blocked SD events and isn't overly accurate. Most digital accelerometers are factory trimmed and will be significantly more accurate. With the the slow nrf51 ADC and software overhead the on time between measuring one axis and the next will make extracting useful data from the accelerometer somewhat difficult.

Most digital accelerometers will have 3 ADCs and latch the data so your measurements are taken at the same time. They also tend to have FIFOs and can be configured to automatically sample at a fixed rate and dump the measurements to the FIFO. That way even when the SD takes over the processor you won't loose samples.

If you are just looking to detect change in motion, many digital accelerometers will provide an interrupt signal and hardware motion thresholds.