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<!doctype html>
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<title>ardx:circ-09[.:wcrs:.]</title>
<meta name="description" content="Arduino Experimenters Kit Photo Resistors circuit">
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<h2><a href="index.html">WCRS</a></h2>
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<ul>
<li><h2>PRODUCTS</h2>
<ul>
<li><a href="https://github.com/WCRSyyc/ardx/"><h3>(WCRS)</h3>ARDX additions</a>
<ul>
<li><a href="preface.html">
<h4>ABOUT</h4>A Few Words</a></li>
<!-- <li><a href="assembling.html">
<h4>ASSMB</h4>Putting It Together</a></li> -->
<li><a href="starthere.html">
<h4>START</h4>Startup Links</a></li>
<li><a href="programming.html">
<h4>PROG</h4>Programming Primer</a></li>
<li><a href="electronics.html">
<h4>ELEC</h4>Electronics Primer</a></li>
<li><a href="fritzing.html">
<h4>FRITZING</h4>Fritzing with ARDX</a></li>
<li><a href="circ01.html">
<h4>CIRC-01</h4>Blinking LED</a></li>
<li><a href="circ02.html">
<h4>CIRC-02</h4>Multiple LEDs</a></li>
<li><a href="circ03.html">
<h4>CIRC-03</h4>Transistors & Motors</a></li>
<li><a href="circ04.html">
<h4>CIRC-04</h4>Servos</a></li>
<li><a href="circ05.html">
<h4>CIRC-05</h4>74HC595 Shift Registers</a></li>
<li><a href="circ06.html">
<h4>CIRC-06</h4>Piezo Speaker</a></li>
<li><a href="circ07.html">
<h4>CIRC-07</h4>Pushbuttons</a></li>
<li><a href="circ08.html">
<h4>CIRC-08</h4>Potentiometers</a></li>
<li><a href="circ09.html">
<h4>CIRC-09</h4>Photo-Resistors</a></li>
<li><a href="circ10.html">
<h4>CIRC-10</h4>Temperature</a></li>
<li><a href="circ11.html">
<h4>CIRC-11</h4>Relays</a></li>
<li><a href="circ12.html">
<h4>CIRC-12</h4>RGB LED blink</a></li>
<li><a href="circ15.html">
<h4>CIRC-15</h4>Dice Simulator</a></li>
</ul>
</li>
<li><a href="https://github.com/WCRSyyc/ardx/"><h3>(WCRS)</h3>Python ARDX</a>
<ul>
<!-- <li><a href="preface.html">
<h4>ABOUT</h4>A Few Words</a></li> -->
<!-- <li><a href="assembling.html">
<h4>ASSMB</h4>Putting It Together</a></li> -->
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<h4>START</h4>Startup Links</a></li> -->
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<h4>PROG</h4>Programming Primer</a></li> -->
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<h4>ELEC</h4>Electronics Primer</a></li>
<li><a href="fritzing.html">
<h4>FRITZING</h4>Fritzing with ARDX</a></li>
<li><a href="ArdxPythonHowTo.html">
<h4>GUIDE</h4>Python Guide</a></li>
<!--
<li><a href="circ01p.html">
<h4>CIRC-01</h4>Blinking LED</a></li>
<li><a href="circ02p.html">
<h4>CIRC-02</h4>Multiple LEDs</a></li>
<li><a href="circ03p.html">
<h4>CIRC-03</h4>Transistors & Motors</a></li>
<li><a href="circ04p.html">
<h4>CIRC-04</h4>Servos</a></li>
<li><a href="circ05p.html">
<h4>CIRC-05</h4>74HC595 Shift Registers</a></li>
<li><a href="circ06p.html">
<h4>CIRC-06</h4>Piezo Speaker</a></li>
<li><a href="circ07p.html">
<h4>CIRC-07</h4>Pushbuttons</a></li>
<li><a href="circ08p.html">
<h4>CIRC-08</h4>Potentiometers</a></li>
<li><a href="circ09p.html">
<h4>CIRC-09</h4>Photo-Resistors</a></li>
<li><a href="circ10p.html">
<h4>CIRC-10</h4>Temperature</a></li>
<li><a href="circ11p.html">
<h4>CIRC-11</h4>Relays</a></li>
<li><a href="circ12p.html">
<h4>CIRC-12</h4>RGB LED blink</a></li>
<li><a href="circ15p.html">
<h4>CIRC-15</h4>Dice Simulator</a></li> -->
</ul>
</li>
<li><a href="http://www.oomlout.com/a/products/ardx/"><h3>(ARDX)</h3>arduino / netduino experimenter´s kit</a>
</li>
</ul>
</li>
</ul>
</section>
<section>
<h3><a rel="license" href="http://creativecommons.org/licenses/by/4.0/">
<img alt="Creative Commons License"
src="img/80x15.png"></a></h3>
This work is licensed under a <a rel="license"
href="http://creativecommons.org/licenses/by/4.0/">Creative Commons
Attribution 4.0 International License</a>.
</section>
</nav>
<main id="circ-09">
<header>
<h1>CIRC<br/>09</h1>
<h2>.:Light:.<br/>.:Photo Resistors:.</h2>
<img src="img/experiments/CIRC-09-square-100.jpg" width="100" height="100" alt="green led and photo resistor on circuit 9 breadboard sheet">
</header>
<h2>(ARDX) .:Arduino Experimentation Kit:. (ARDX)</h2>
<section>
<h2>What We're Doing</h2>
<p>Whilst getting input from a potentiometer can be useful for human controlled experiments, what do we use when we want an environmentally controlled experiment? We use exactly the same principles but instead of a potentiometer (twist based resistance) we use a photo resistor (light based resistance). The Arduino cannot directly sense resistance (it senses voltage) so we set up a <a href="https://github.com/WCRSyyc/ardx/wiki/voltage-divider">voltage divider</a> (<a href="https://en.wikipedia.org/wiki/Voltage_divider">http://ardx.org/VODI</a>). The exact voltage at the sensing pin is calculable, but for our purposes (just sensing relative light) we can experiment with the values and see what works for us. A low resistance value will occur when the sensor is well lit while a high value will occur when it is in darkness.</p>
</section>
<section id="circuit">
<h2>The Circuit</h2>
<div id="CIRC-theparts">
<h3>The Parts</h3>
<table>
<tr>
<td><img src="img/parts/CIRC-09-3dsheet-60.png"
width="60" height="36" alt="circuit 9 breadboard sheet 3d view"/></td>
<td>CIRC-09<br/>Breadboard Sheet<br/>x1</td>
<td><img src="img/parts/HEAD-02-60.png"
width="60" height="36" alt="2 pin header"/></td>
<td>2 Pin Header<br/>x4</td>
<td><img src="img/parts/IC-PHOTO-01-60.png"
width="60" height="36" alt="photo resistor"/></td>
<td>Photo-Resistor<br/>x1</td>
<td><img src="img/parts/WIRE-01-60.png"
width="60" height="36" alt="wire"/></td>
<td>Wire</td>
</tr><tr>
<td><img src="img/parts/RES-103-60.png"
width="60" height="36" alt="10k ohm resistor"/></td>
<td>10k Ohm Resistor<br/>Brown-Black-Black-Red<br/>x1</td>
<td><img src="img/parts/RES-561-60.png"
width="60" height="36" alt="560 ohm resistor"/></td>
<td>560 Ohm Resistor<br/>Green-Blue-Black-Black<br/>x1</td>
<td><img src="img/parts/LED-05G-60.png"
width="60" height="36" alt="green LED"/></td>
<td>Green LED<br/>x1</td>
<td colspan="2"></td>
</tr>
</table>
</div>
<span class="bb-svg-container"><svg
xmlns="http://www.w3.org/2000/svg"
xmlns:xlink="http://www.w3.org/1999/xlink"
viewBox="30 13 70 70"
preserveAspectRatio="xMaxYMin meet">
<image height="100" width="100"
xlink:href="img/experiments/CIRC09-bb.svg"/>
</svg></span>
<div>
<h3>Schematic</h3>
<span class="sch-svg-container"><svg
xmlns="http://www.w3.org/2000/svg"
xmlns:xlink="http://www.w3.org/1999/xlink"
viewBox="63 42 37 37"
preserveAspectRatio="xMidYMin meet">
<image height="100" width="100"
xlink:href="img/experiments/CIRC09-sch.svg" />
</svg></span>
</div>
<div>
<h3>Resources</h3>
<h4>.:download:.</h4>
<p>Breadboard layout sheet<br/>
<a href="img/experiments/CIRC09-sheet-OOML.pdf">http://ardx.org/BBLS09</a>
</p>
<p>Fritzing diagram<br/><a href="fritzing/CIRC09.fzz">
https://wcrsyyc.github.io/ardx/fritzing/CIRC09.fzz</a></p>
<h4>.:view:.</h4>
<p>
assembly video<br/>
<a href="https://www.youtube.com/watch?v=5WOPv9WEi4Q">http://ardx.org/VIDE09</a>
</p>
</div>
</section>
<section id="code">
<h2>Code <span>(no need to type everything in just)</span></h2>
<p>Download the Code from ( <a
href="code/CIRC09-code.txt">
http://ardx.org/CODE09</a> )<br/>
(and then copy the text and paste it into an empty Arduino Sketch)</p>
<pre>/*
* A simple program that will change the intensity of an LED based
* on the amount of light incident on the photo resistor.
*/
//PhotoResistor Pin
int lightPin = 0; //the analog pin the photoresistor is connected to
//LED Pin
int ledPin = 9; //the pin the LED is connected to
//we are controlling brightness so
//we use one of the PWM (pulse width
// modulation pins)
void setup()
{
pinMode(ledPin, OUTPUT); //sets the led pin to output
}
/*
* loop() - this function will start after setup
* finishes and then repeat
*/
void loop()
{
int lightLevel = analogRead(lightPin); //Read the light level
//the photoresistor is not calibrated to any units so
//this is simply a raw sensor value (relative light)
lightLevel = map(lightLevel, 0, 900, 0, 255);
//adjust the value 0 to 900 to
//span 0 to 255
lightLevel = constrain(lightLevel, 0, 255);//make sure the
//value is between
//0 and 255
analogWrite(ledPin, lightLevel); //write the value
}</pre>
</section>
<section id="CIRC-notworking">
<h2>Not Working? <span>(3 things to try)</span></h2>
<div>
<h3>LED Remains Dark</h3>
<p>This is a mistake we continue to make time and time again, if only they could make an LED that worked both ways. Pull it up and give it a twist.</p>
</div>
<div>
<h3>It Isn't Responding to Changes in Light.</h3>
<p>Given that the spacing of the wires on the photo-resistor is not standard, it is easy to misplace it. Double check it´s in the right place.</p>
</div>
<div>
<h3>Still not quite working?</h3>
<p>You may be in a room which is either too bright or dark. Try turning the lights on or off to see if this helps. Or if you have a flashlight nearby give that a try.</p>
</div>
</section>
<section id="CIRC-makingBetter">
<h2>Making it Better?</h2>
<h3>Reverse the response:</h3>
<p>Perhaps you would like the opposite response. Don't worry we can easily reverse this response just change:<br/>
<code>analogWrite(ledPin, lightLevel);</code> ----> <code>analogWrite(ledPin, 255 - lightLevel);</code><br/>
Upload and watch the response change:</p>
<h3>Night light:</h3>
<p>Rather than controlling the brightness of the LED in response to light, lets instead turn it on or off based on a threshold value. Change the loop() code with.</p>
<pre>void loop(){
int threshold = 300;
if(analogRead(lightPin) > threshold){
digitalWrite(ledPin, HIGH);
}else{
digitalWrite(ledPin, LOW);
}
}</pre>
<h3>Light controlled servo:</h3>
<p>Lets use our newly found light sensing skills to control a servo (and at the same time engage in a little bit of Arduino code hacking). Wire up a servo connected to pin 9 (like in CIRC-04). Then open the Knob example program (the same one we used in CIRC-08) File > Examples > Library-Servo > Knob. Upload the code to your board and watch as it works unmodified.</p>
<h3>Using the full range of your servo:</h3>
<p>You'll notice that the servo will only operate over a limited portion of its range. This is because with the <a href="https://github.com/WCRSyyc/ardx/wiki/voltage-divider">voltage dividing</a> circuit we use the voltage on analog pin 0 will not range from 0 to 5 volts but instead between two lesser values (these values will change based on your setup). To fix this play with the val = map(val, 0, 1023, 0, 179); line. For hints on what to do visit <a href="http://arduino.cc/en/Reference/Map">http://arduino.cc/en/Reference/Map</a>. HINT: It is also a good idea to make sure that the requested servo position stays in the valid range of 0 to 180. To combine that with the map function, you can use something like</p>
<pre>val = constrain( map( val, 100, 900, 0, 180 ), 0, 180 );</pre>
<p>to say that values of 100 to 900 will translate to angles from 0 to 180 degrees, but still keep in the valid range if the input value is less than 100 or greater than 900.</p>
</section>
</main>
<footer>.:Welcome to the Bottom:.</footer>
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