Calculating distance ?

RE: Calculating distance ?

Vidar Berg — Thu, 14 Jan 2021 08:18:25 GMT

I'm afraid this is something you have to debug yourself. total_distance = distance[0]+distance[n] is supposed to be 64m + 52m, right? In that case, I'd suggest you start by checking what happens to distance[0]. Maybe it's always getting overwritten by the current distance..

RE: Calculating distance ?

RixtronixLAB — Wed, 13 Jan 2021 14:47:43 GMT

From my observation :

nfo> app: Computed distance raw: 93984 m <===

nfo> app: Computed distance raw: 94048 <===

nfo> app: Computed distance value: 64 m <=== this is right

nfo> app: Computed distance raw: 94048 <===

nfo> app: Computed distance raw: 94100 <===

nfo> app: Computed distance value: 52 m <=== this is right 94100 - 94048 but total distance suppose to be 64m + 52m .....

code :
distance = (m_speed_calc_data.acc_rev_cnt - m_speed_calc_data.prev_acc_rev_cnt)*(WHEEL_CIRCUMFERENCE/1000);

total_distance = distance[0]+distance[n] ?

Any clues ? thanks

RE: Calculating distance ?

RixtronixLAB — Tue, 12 Jan 2021 14:33:40 GMT

Is m_speed_calc_data.acc_rev_cnt += rev_cnt - m_speed_calc_data.prev_rev_cnt; equal to this ?

RE: Calculating distance ?

RixtronixLAB — Tue, 12 Jan 2021 14:25:02 GMT

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

RE: Calculating distance ?

RixtronixLAB — Tue, 12 Jan 2021 13:52:26 GMT

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

RE: Calculating distance ?

Vidar Berg — Tue, 12 Jan 2021 13:38:40 GMT

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()

RE: Calculating distance ?

RixtronixLAB — Tue, 12 Jan 2021 13:26:25 GMT

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

RE: Calculating distance ?

Vidar Berg — Tue, 12 Jan 2021 12:10:36 GMT

Hello,

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