How to use a SHARP GP2Y0A21YK0F IR Distance Sensor with Arduino

SHARP GP2Y0A21YK0F IR distance sensor

The SHARP GP2Y0A21YK0F is a relatively easy to use IR distance sensor with a range of 10 – 80 cm. It is a great sensor to use for autonomous robots or non-contact optical switches.

In this tutorial you will learn how the sensor works and how to use it with Arduino. I have included a wiring diagram and example code so you can start experimenting with your sensor.

If you are looking for a sensor with more range or a waterproof distance sensor, take a look at the HC-SR04 or JSN-SR04T. In the articles below I explain how these distance/proximity sensors work and how you can use them with Arduino.

Other distance/proximity sensors

If you just want to use the sensor you can skip the theory below, but you might find it interesting to know how these sensors work.

How does an IR distance sensor work?

An IR distance sensor uses a beam of infrared light to reflect off an object to measure its distance. The distance is calculated by using triangulation of the beam of light. The sensor consists of an IR LED and a light detector or PSD (Position Sensing Device). When the beam of light gets reflected by an object, the reflected beam will reach the light detector and an ‘optical spot’ will form on the PSD.

When the position of the object changes, the angle of the reflected beam and the position of the spot on the PSD changes as well. See point A and point B in the image below.

How an IR distance sensor works
Note the change in the angle of the reflected beam and the position of the 'optical spot' on the PSD

The sensor has a built-in signal processing circuit. This circuit processes the position of the optical spot on the PSD to determine the position (distance) of the reflective object. It outputs an analog signal which depends on the position of the object in front of the sensor.

How to read an IR distance sensor?

IR distance sensors output an analog signal, which changes depending on the distance between the sensor and an object. From the datasheet you can see that the output voltage of the SHARP GP2Y0A21YK0F ranges from 2.3 V when an object is 10 cm away to 0.4 V when an object is 80 cm away. The graph also shows why the usable detection range starts at 10 cm. Notice that the output voltage of an object that is 2 cm away is the same as the output voltage for an object that is 28 cm away. The usable detection range therefore start after the peak at roughly 10 cm or 2.3 V.

GP2Y0A21YK0F Output Characteristics
Distance measuring characteristics (output)

The graph also shows the drawback of these sensors, the response is non-linear. In other words, a big change in the output voltage does not always correspond to a big change in range. In order to determine the distance between the sensor and an object, you need to find a function that converts the output voltage into a range value.

This can be done using MS Excel and results in the following formula for distances > 10cm:

Distance (cm)= 27.726X POW(Output_voltage, -1.2045)

This is the function that is used in the SharpIR library, which we will be using later. Note that this function is based on data from the SHARP datasheet only. The output characteristics of the sensor will vary slightly from sensor to sensor so you might get inaccurate readings. 

If you want to improve the accuracy of your readings, you can try to measure and plot many data points in Excel and fit a curve through these points. Once you have a new function for your specific sensor, you will need to change the formula used in the SharpIR.cpp file.

GP2Y0A21YK0F Specifications

Operating voltage4.5 to 5.5 V
Operating current30 mA
Measuring range10 to 80 cm
Output typeAnalog
Dimensions29.5x13x13.5 mm
Mounting holes2x 3.2 mm, 37 mm spacing

For more information you can check out the datasheet here.

Tools and Materials

You can find the tools and materials needed for this tutorial in the links below. Or click the markers in the image for more info and prices on Amazon.

*Note: the above links are affiliated which means – at no additional cost to you – if you purchase anything using them you’re helping to support my work on this site. My humble thanks (I really appreciate it)! 

Wiring - Connecting GP2Y0A21K0F IR Sensor to Arduino

The wiring diagram below shows you how to connect the GP2Y0A21YK0F IR distance sensor to an Arduino.

SHARP GP2Y0A21YK0 with Arduino Wiring Diagram
GP2Y0A21YK0F IR distance sensor with Arduino​ wiring diagram

These type of distance sensors tend to be a bit noisy, so it is recommended to add a capacitor between Vcc and GND. The datasheet suggests a capacitor of 10 µF or more (I used 220 µF). Connect the positive lead of the capacitor to the Vcc wire connection and the negative lead to the GND wire connection (see picture). Capacitors are often marked with a stripe which indicates the negative lead. The positive lead is often longer then the negative lead.

GP2Y0A21YK0F Connections

1 (Yellow)A0
2 (Black)GND
3 (Red)5V

If your sensor comes with different colored wires, be sure to check the pinout below. The Vo pin is connected to the analog in of the Arduino (A0). 

GP2Y0A21YK0F IR distance sensor pinout

Now that you have wired up the sensor it is time to look at some example code.

Example code for SHARP GP2Y0A21YK0F IR sensor with Arduino and SharpIR library

The SharpIR library written by Guillaume Rico and Thibaut Mauon makes working with SHARP IR sensors a lot easier. It includes the formulas that are needed to convert the measured output voltage to a distance in centimeters. Currently the library supports the following sensors: GP2Y0A02YK0F, GP2Y0A21YK0F, GP2Y0A710K0F and GP2YA41SK0F. The latest version of the library can be downloaded here on GitHub or click the button below.

You can install the library by going to Sketch > Include Library > Add .ZIP Library in the Arduino IDE.

The author of the library mentioned that the readings from the sensor can fluctuate quite a bit. The library solves this problem by taking multiple readings in a row, discarding outliers and taking the mean to get a more stable distance reading. Currently the library takes the mean of 25 readings, which takes roughly 53 ms.

The example code below can be used with the GP2Y0A21YK0F sensor and displays the measured distance in centimeters in the serial monitor. 

/*SHARP GP2Y0A21YK0F IR sensor with Arduino and SharpIR library example code. More info: */

//Include the library
#include <SharpIR.h>
//Define model and input pin
#define IRPin A0
#define model 1080
/*Model :
GP2Y0A02YK0F --> 20150
GP2Y0A21YK0F --> 1080
GP2Y0A710K0F --> 100500
GP2YA41SK0F --> 430
//Setup the sensor object
SharpIR IR_Sensor_1(IRPin, model);
void setup()
//Begin serial communication at a baud rate of 9600
void loop()
int distance_cm = IR_Sensor_1.distance();  // this returns the distance to the object you're measuring
Serial.print("Mean distance: ");  // returns it to the serial monitor
Serial.println(" cm");

Note that we have called the sensor ‘IR_Sensor_1’ in this example. If you want to use multiple IR distance sensors, you can create another sensor object with a different name: SharpIR IR_Sensor_2(IRPin2, model); Note that in that case you also use a different input pin for the second sensor.

You should get the following output in the serial monitor (Ctrl + Shift +M).

SHARP GP2Y0A21YK0F serial monitor output
Serial monitor output


In this article I have shown you how the SHARP GP2Y0A21YK0F IR distance sensor works and how you can use it with Arduino. I hope you found it useful and informative. If you did, please share it with a friend that also likes electronics!

I would love to know what projects you plan on building (or have already built) with this IR distance sensor. Please leave a comment down below and share your ideas.

Share on facebook
Share on twitter
Share on linkedin
Share on pinterest
Share on email
Share on whatsapp


Creative Commons License

If you have any questions, suggestions or if you think that things are missing in this tutorial, please leave a comment down below. Note that comments are held for moderation in order to prevent spam.

2 Responses

    1. Hi,

      I just retested the code and it seemed to run fine, although there might have been a small problem in the name I chose for the sensor object. I changed it to ‘IR_Sensor_1’. Could you retry the code and let me know if it works for you? Make sure you have the correct library installed and that you copy the entire code before modifying it.


Leave a Reply

Your email address will not be published. Required fields are marked *