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Sharp-Average-IR

Arduino Library for Sharp IR Sensors. See the readme.md file of the master branch (v1.0) for a little bit of background history on this library.

What's new in v2.0

  • The distance is given as a float instead of an integer.
  • Much better way to sort out out-of-tolerance values.
  • Gives better accuracy.
  • GP2Y0A02Y and GP2Y0A710K0F sensors are also supported.

How it works

The Sharp IR sensors are cheap but somehow unreliable. I've found that when doing continuous readings to a fix object, the distance given oscillates quite a bit from time to time. For example I had an object at 31 cm. The readings from the sensor were mainly steady at the correct distance but eventually the distance given dropped down to 25 cm or even 16 cm. That's quite a bit and for some applications it is quite unacceptable. I checked the library http:code.google.com/p/gp2y0a21yk-library/ by Jeroen Doggen and what the author was doing is to take a bunch of readings and give an average of them

This library works similarly. It reads a bunch of readings (avg) and then it calculates the average. Then it checks every reading to see how much it deviates from the average. If it is out of the tolerance given by the user, it is rejected. At the end a new Average Distance is calculated without the dismissed values. You might find the concept familiar if you know about statistics and the concept of standard deviation.

The distance is calculated from a formula extracted from the graphs on the sensors datasheets. Since this library takes some measurements before giving a final result, it is not as responsive as direct measurements.

This library has the formulas to work with the GP2Y0A21Y, GP2Y0A02YK, GP2Y0A02Y and GP2Y0A710K0F sensors but expanding it for other sensors with similar behaviour should be easy enough.

Setting it up

I won't be explaining how to copy the library into your Arduino IDE, it's well documented. But you have to do it.

1. Import Library:

<include "SharpAverageIR.h>

2. Initialize an object:

SharpAverageIR sharp(irPin, avg, tolerance, model); //I called the object sharp in this example

  • irPin is the Analog Pin in which the sensor is attached.
  • avg is an Int representing the number of measurements it will take.
  • tolerance is the requested tolerance among values. It is an Int between 1 and 100. Experiment with it.
  • model it is an Int which represent the sensor in use.
  • use 0 or 1080 on the constructor for the GP2Y0A21Y (from 10 to 80cm)
  • use 1 or 20150 on the constructor for the GP2Y0A02Y (from 20 to 150cm)
  • use 2 or 0430 on the constructor for the GP2Y0A41SK0F (from 04 to 40cm)
  • use 3 or 10550 on the constructor for the GP2Y0A710K0F (from 100 to 550cm)

3. Call the public method:

float dis=sharp.distance(); //this method returns a float with the distance.

Please see the example provided on this Library.