Arduino based accurate distance measurement for sharp GP2Y0A21YK

The aim of this post is to explain how to convert voltage from Sharp ranging sensor into an accurate distance. Experiments have been performed with Sharp GP2Y0A21YK distance sensors. The range of this triangulation-based sensors is from 10cm to 80cm.

Measurement campaign

An accurate measurement experimental campaign has been performed. Range has been measured with a step of 10mm. The following graph show the behavior of the GP2Y0A21YK sensor according to the distance (ADC value vs distance). As it is explained in the sensor’s specifications the sensor is not suited for measurements below 10cm due to ambiguity.

ADC value versus distance for the Sharp distance sensor GP2Y0A21YK

Polynomial approximation

Thanks to the Matlab polyfit fonction, the curv has been approximated with a fourth degree polynomial. The approximation covers the range from 1.5cm to 80cm. The following figure shows the result:

Distance polynomial approximation of the Sharp distance sensor GP2Y0A21YK

Results

The approximation for the GP2Y0A21YK is given by the following equation. \(ADC\) is the raw value returned by the Arduino analogRead() function in range from 0 to 1024 (10 bits analog to digital converter).

$$ Distance = 200.3775040589502 \\ - 2.2657665648980.ADC \\ + 0.0116395328796 .ADC^2 \\ -0.0000299194195.ADC^3 \\ + 0.0000000374087 .ADC^4 \\ - 0.0000000000181.ADC^5 $$

Based on this result, a C++ function can easily be written in order to compute the distance:

/*!
    \brief  make a distance measurement with a Sharp GP2Y0A21YK sensor
    \return the measured distance in mm

*/
float get_Sharp_GP2Y0A21YK_Distance(int PinID)
{
    // Read analog to digital converter value
    float ADCValue = (float)analogRead(PinID);

    // Convert in millimeters and return distance
    return  200.3775040589502
            - 2.2657665648980 * ADCValue
            + 0.0116395328796 * ADCValue * ADCValue
            - 0.0000299194195 * ADCValue * ADCValue * ADCValue
            + 0.0000000374087 * ADCValue * ADCValue * ADCValue * ADCValue
            - 0.0000000000181 * ADCValue * ADCValue * ADCValue * ADCValue * ADCValue;
}

Download

Excel files, images, raw data and Matlab scripts can be downloaded here:

SHARP_Distance_Sensors.zip

See also


Last update : 06/11/2018