MMA8451 Simple Pedometer

[federicovilli]

I'm trying to find the simplest way to make a not too much accurate pedometer (20% error) with MMA8451.

To achieve that goal I have understand that first of all I have to configure MMA8451 properly to obtain the right data (not too few neither too much) from accelerometer.
Then I have to pull out steps from data !!

I'm looking for any kind of suggestion ...
Tnx

[diegoadrian]

Hello Federico,

Thank you for writing.

In your case, I highly recommend you to use the MMA9553. The MMA9553 is an intelligent motion sensing pedometer, and is much more easy to make a pedometer with this IC than with the MMA8451.

This is how you can configure the MMA9553.

void MMA9553L_Init(void){

     pedometer_config();          // Write all the Pedometer configuration
     pedometer_enable();          // Enable the Pedometer application
     pedometer_active();
     pedometer_wakeup();          // Disable Sleep Mode and enable Wake-up Mode

}‍‍‍‍‍‍‍‍

The pedometer_config function, is the following.

void pedometer_config(void){

     unsigned char MBx[20]= {0x15, 0x20, 0x00, 0x10,
                       SLEEP_MIN_MSB, SLEEP_MIN_LSB,
                    SLEEP_MAX_MSB, SLEEP_MAX_LSB,
                    SLEEP_COUNT_THR_MSB, SLEEP_COUNT_THR_LSB,
                    CONFIG, STEP_LENGTH,
                    HEIGHT, WEIGHT, FILTER_STEP,
                    MALE_FILTER_TIME, STEP_PERIOD,
                    STEP_COALESCE, ACT_COUNT_THR_MSB,
                    ACT_COUNT_THR_LSB};

     I2C_WriteMultiRegisters(MMA9553L_ADDRESS, MMA9553_SUB_ADDR, sizeof(MBx), MBx);

}‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

The pedometer_enable function, is the following.

void pedometer_enable(void){

     unsigned char MBx[5]={0x17, 0x20, 0x05, 0x01, 0x00};

     I2C_WriteMultiRegisters(MMA9553L_ADDRESS, MMA9553_SUB_ADDR, sizeof(MBx), MBx);
}‍‍‍‍‍‍

The pedometer_active function, is the following.

void pedometer_active(void){

     unsigned char MBx[5]={0x15, 0x20, 0x06, 0x01, 0x80};

     I2C_WriteMultiRegisters(MMA9553L_ADDRESS, MMA9553_SUB_ADDR, sizeof(MBx), MBx);

}‍‍‍‍‍‍‍

The pedometer_wakeup function, is the following.

void pedometer_wakeup(void){

     unsigned char MBx[5]={0x12, 0x20, 0x06, 0x01, 0x00};

     I2C_WriteMultiRegisters(MMA9553L_ADDRESS, MMA9553_SUB_ADDR, sizeof(MBx), MBx);
}
‍‍‍‍‍‍

This is how you could read the steps.

void Read_Step(void)
{
     pedometer_cmd_readstatus();

     I2C_ReadMultiRegisters(MMA9553L_ADDRESS, MMA9553_SUB_ADDR, 2, MBx);
     if (MBx[1]==0x80){ // Is COCO flag set?
          I2C_ReadMultiRegisters(MMA9553L_ADDRESS, MMA9553_SUB_ADDR, sizeof(MBx), MBx); // 12 bytes status data + 4 bytes frame start

          StepCount = ((short) (MBx[6]<<8 | MBx[7]));
          // Send the step count to the terminal
          //Hex_to_Dec(StepCount);
     }
}‍‍‍‍‍‍‍‍‍‍‍‍‍

The pedometer_cmd_readstatus function is the following.

void pedometer_cmd_readstatus(void){

     unsigned char MBx[4]={0x15, 0x30, 0x00, 0x0C};

     I2C_WriteMultiRegisters(MMA9553L_ADDRESS, MMA9553_SUB_ADDR, sizeof(MBx), MBx);
}‍‍‍‍‍‍

Finally, these are the macros that you are going to need.

#define MMA9553L_ADDRESS      0x4C
#define MMA9553_SUB_ADDR      0x00

#define SLEEP_MIN_MSB           0x0C
#define SLEEP_MIN_LSB           0xE0
#define SLEEP_MAX_MSB           0x13
#define SLEEP_MAX_LSB           0x20
#define SLEEP_COUNT_THR_MSB 0x00
#define SLEEP_COUNT_THR_LSB 0x96
#define CONFIG                    0x60
#define STEP_LENGTH               0x50
#define HEIGHT                     0xAA          // Height in centimeters, 170 (0xAA)
#define WEIGHT                     0x44          // Weight in kilograms, 68 (0x44)
#define FILTER_STEP           0x04
#define MALE_FILTER_TIME     0x03          // Male
#define STEP_PERIOD           0x05
#define STEP_COALESCE           0x01
#define ACT_COUNT_THR_MSB   0x00
#define ACT_COUNT_THR_LSB   0x00
‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

I hope this information will be useful for you.

Best Regards,

Diego