Calculating distance ?

[RixtronixLAB]

Dear Member,

I want to calculate distance I have traveled,

I saw variables as

#define WHEEL_CIRCUMFERENCE         2070                                                            /**< Bike wheel circumference [mm] */

static uint32_t calculate_speed(int32_t rev_cnt, int32_t evt_time)

distance = rev_cnt * (WHEEL_CIRCUMFERENCE/1000); //divide by 1000 for per metre

but the output doesn't make sense

nfo> app: Computed distance value: 52052 m
                         

any clues ? Do I need to add any coefficient ? which coefficient ?

is this variable BSC_PROFILE_speed_rev_count equal to wheel rotation speed ?

thanks

[Vidar Berg]

Hello,

The distance function looks to be correct, so I think 'rev_cnt ' must be wrong.

[RixtronixLAB]

Hi Vidar,if 'rev_cnt' must be wrong, which variable should I use for calculating distance based on tyre size and tyre revolution  ?

Complete function I see from main.c

static uint32_t calculate_speed(int32_t rev_cnt, int32_t evt_time)
{
    static uint32_t computed_speed   = 0;
     //distance = (rev_cnt * (WHEEL_CIRCUMFERENCE/1000)); //divide by 1000 for per metre
			
    if (rev_cnt != m_speed_calc_data.prev_rev_cnt)
    {
        m_speed_calc_data.acc_rev_cnt  += rev_cnt - m_speed_calc_data.prev_rev_cnt;
        m_speed_calc_data.acc_evt_time += evt_time - m_speed_calc_data.prev_evt_time;

        /* Process rollover */
        if (m_speed_calc_data.prev_rev_cnt > rev_cnt)
        {
            m_speed_calc_data.acc_rev_cnt += UINT16_MAX + 1;
        }
        if (m_speed_calc_data.prev_evt_time > evt_time)
        {
            m_speed_calc_data.acc_evt_time += UINT16_MAX + 1;
        }

        m_speed_calc_data.prev_rev_cnt  = rev_cnt;
        m_speed_calc_data.prev_evt_time = evt_time;

        computed_speed = SPEED_COEFFICIENT *
                         (m_speed_calc_data.acc_rev_cnt  - m_speed_calc_data.prev_acc_rev_cnt) /
                         (m_speed_calc_data.acc_evt_time - m_speed_calc_data.prev_acc_evt_time);

        m_speed_calc_data.prev_acc_rev_cnt  = m_speed_calc_data.acc_rev_cnt;
        m_speed_calc_data.prev_acc_evt_time = m_speed_calc_data.acc_evt_time;
    }

    return (uint32_t)computed_speed;
}

Thanks

[Vidar Berg]

Hi,

I meant to say that the 'rev_cnt' input value had to be wrong as you didn't get the expected result. I'd suggest you try to test with fixed inputs to verify the function. E.g., check if you get the distance to be ~2000 m if you pass rev_cnt=1000 to calculate_speed()

[RixtronixLAB]

You mean, I use Garmin device to check the distance and compare with the code ? thanks

[RixtronixLAB]

I used this equation : 

 distance = ((rev_cnt * (WHEEL_CIRCUMFERENCE/1000)))/135; //divide by 1000 for per metre
                                                                //135 is the coefficient to m distance

and it looks like more accurate comparing wth my Garmin Edge,

app: Computed distance value: 685 m

in Garmin Edge is 627 m

How do you reckon ? thanks