How to make a Sharp IR sensor linear

Sharp sensor graph

Sharp IR proximity sensors are cheap and easy to use, but do not produce linear output. NOTE: this is a different issue than noise or jitter in the sensor data. That can be fixed with capacitors to ensure stable power – read this for explanation.

Here is one simple conversion to linear for the commonly used GP2YOA1YK sensor, accuracy is about +/-5%, but its drawback is that pow() is a slow function on the Arduino:

// Linearize Sharp GP2YOA1YK
float distance = 12343.85 * pow(sensorValue, -1.15) // centimeters

Here is a library that uses a lookup table – a much faster method because no calculations are done on the fly, it’s all done beforehand (you can see the list if you look inside DistanceGP2Y0A21YK_LUTs.h (LUT = Look Up Table) –

Here is an equation tweaked for the longer range Sharp GP2Y0A02YK:

// Linearize Sharp GP2Y0A02YK
float distance = 30431 * pow(sensorValue, -1.169) // centimeters
// *or: *
float distance = 21208 * pow(sensorValue, -1.251) // inches

Here is a similar conversion function for the Sharp GPD212:

If you measure values yourself, you can make an array of values and this is a very efficient way to look up those values (an example is included for the Sharp 2Y0A02):

Here is another solution that gives you a universal function that can be calibrated for different sensors (more info):
typedef const struct
const signed short a;
const signed short b;
const signed short k;

// Parameters for GP2Y0A21YK sensor
const ir_distance_sensor GP2Y0A21YK = { 5461, -17, 2 };

// Converting the values of the IR distance sensor to centimeters
// Returns -1 if the conversion did not succeed
signed short ir_distance_calculate_cm(ir_distance_sensor sensor,
unsigned short adc_value)
if (adc_value + sensor.b < 0)
return -1;

return sensor.a / (adc_value + sensor.b) - sensor.k;


Here is another accurate function that also accounts for how curve changes when <10cm, if you have other sensors detecting that (normally objects that close give unusable values with this sensor):

2 thoughts on “How to make a Sharp IR sensor linear

Add yours

  1. Hi Eric,
    I am a student of NYU working on proximity sensor to detect human at certain distance. Your libraries helped for reference in my project. I have used your code for calibration but I am not getting good results. I have given 5.3 V power supply externally to the GP2YOA1YK and tried with Arduino Vcc also but not getting correct distance values. I was unable to understand how to set up a look up table which you set for your sensor. Please help me to get calibrated value of my sensor. Thanks

    Reply back on my mail:


    1. Unless you have an extremely performance sensitive application, don’t bother with a lookup table. For the sensor you’re using, just use the simple conversion referenced above:
      float distance = 12343.85 * pow(sensorValue, -1.15) // centimeters

      If you still want to use a lookup table but confused about how to implement it, try this library


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

Create a website or blog at

Up ↑

%d bloggers like this: