How is the INT1_THS scaled on the LIS3DH sensor?
I try to use the LIS3DH as a fall sensor in an security device for elderly people.
I want to use a more elaborate detection method than just using the free fall interrupt and therefore I try to define a fall as first a free fall interrupt and then an activity or "wake-up" interrupt.
For the freefall everything works as expected. I set up the registers as follows:
Write (0x25): 0x02 //Change active high to active low
Write (0x20): 0x57 //Enable all axis with 100Hz
Write (0x22): 0x40 //Enable Interrupt on INT1
Write (0x23): 0x00 //fs 2g
Write (0x24): 0x08 //Latch interrupt
Write (0x33): 0x02 //Duration 20ms
Write (0x32): 0x1f //Threshold 16mg * 31 = 496mg
Write (0x30): 0x95 //AND of x,y,z low events
After I receive the Interrupt I then change the configuration to the following:
Write (0x20): 0x57 //Enable all axis with 100Hz
Write (0x22): 0x40 //Enable Interrupt on INT1
Write (0x23): 0x20 //fs - 10: ±8 g
Write (0x24): 0x08 //Latch interrupt
Write (0x33): 0x01 //Duration 10ms
Write (0x32): 0x20 //1 LSb = 62 mg @ FS = ±8 g -> Threshold 62mg * 32 = 1984mg
Write (0x30): 0x2a //OR of x,y,z high events
The problem I experience is that apparently the scale of the treshold register is not 62mg/LSB but 32mg/LSB as I get an interrupt if 1g is slightly exceeded and not 2g as expected.
If I set the threshold to 0x41 * 32mg = 2080mg I only get the interrupt if the acceleration exceeds 2g.
Do I have a false assumption somewhere? Or am I configuring something wrong?
Thanks for your help.