MMA8653FC as pedometer counter

[roysit]

Hi,all

     I'm using MMA8653FC. and I don't know how to implement a pedometer aglorithm.

I't there demo source code?

Regards,

Roy

[TomasVaverka · Accepted solution]

Roy,

Currently, I am not aware of any implementations of pedometer algorithms using the MMA8653FC.

There is available the MMA9553L intelligent pedometer platform that allows the user to customize and control the behavior of the pedometer application using a few configuration registers and report back the measured and calculated data using several status registers. For more information on this device, have a look at the MMA9553LSWRM.

Regards,

Tomas

[roysit]

Tomas,

1. Thanks for your advise.According to our project, MMA8653 is more suitable. Since we already have a 8051 compatible soc chip. So we have to implement the

pedometer algorithm on it.

2. The MMA8653FC does have a low-pass filter. can the cutoff frequency be change?

Regards,

Roy

[TomasVaverka]

Roy,

The low-pass filter on the MMA8653FC is a simple 1st order decimation filter, i.e. a moving average filter followed by a down-sampling.  Its cut-off frequency depends on the selected ODR (DR[2:0] bits) and mode ((S)MODS[1:0] bits).

If you look at Table 62 in the datasheet, you will find a column "OS Ratio" for all possible ODR/(S)MODS combinations. This table allows you to calculate the ADC frequency, following the formula:

ADC freq = OS Ratio * ODR

The low-pass filter does a decimation by either 2 or 4, according to the following rule, and the cut-off frequency depends on the decimation rate:

OS Ratio = 2:  decimation by 2, cut-off freq = 0.25 * ADC freq

OS Ratio >= 4: decimation by 4, cut-off freq = 0.114 * ADC freq

Regards,

Tomas

[roysit]

Hi, Tomas:

    It's helpful. Thank you!

Regards,

Roy