Step 2: Testing and Connecting your photocell

Testing your photocell

The easiest way to determine how your photocell works is to connect a multimeter in resistance-measurement mode to the two leads and see how the resistance changes when shading the sensor with your hand, turning off lights, etc. Because the resistance changes a lot, an auto-ranging meter works well here. Otherwise, just make sure you try different ranges, between 1M ohms and 1K ohms before 'giving up'

Connecting to your photocell

Because photocells are basically resistors, they are non-polarized. That means you can connect them up 'either way' and they'll work just fine!

Photocells are pretty hardy, you can easily solder to them, clip the leads, plug them into breadboards, use alligator clips, etc. The only care you should take is to avoid bending the leads right at the epoxied sensor, as they could break off if flexed too often.
<p>This is pretty fun, yet kinda annoying.</p>
<p>What is the appropriate sensor to measure intensity of blue light</p>
<p>i want to use multiple LDRs and collect data at the same time of resistance , how can i colllect it from multiple LDR system.</p>
<p>photos taken from this pdf... https://learn.adafruit.com/downloads/pdf/photocells.pdf</p>
<p>hi pls help me i want to ask that can photocell respond to red laser light?</p>
<p>Silly Q: is it possible to break a photocell by supllying it too much light (for example using a phone's led?) <br></p>
I'm a bit confused with a project I'm working on. I'm trying to add a LDR to a 6V DC battery powered strobe light. I assumed that I could just put it in line either between + and on/off switch, on/off and petentiometer, or between - and circuit board connection. None of these connections have worked. Do I need to build an additional circuit for the LDR to work?
<p>Great tutorial :D May you tell me the app where you read the graph and in which format? I would really need it for an important contest.. Thanks in advance :)</p>
<p>Thanks for the great ible. This has answered a lot of questions I had about photocells and using them with Arduino.</p>
Is it possible to get photo sensors that are sensitive to other colors, like blue/UV or IR?
Really nice tutorial. There is another photoresistor setup, that's worth mentioning. Instead of having a variable resistor (in this case a photoresistor) connected to the positive and a fixed resistor connected to ground, you could use two photoresistors (schematic shown below). this is called a differential light sensor. This setup can be used to measure the difference between the two sensors with one analog input. If the two sensors are exposed to the same amount of light, the readout on the ADC pin should be around 512, if the microcontroller has a 10 bit resolution. If the photoresistor connected to ground is exposed to more light than the other one, the analog voltage would drop, and if the photoresistor connected to positive is exposed to more light, the voltage would rise.
Sorry. The schematic, I uploaded somehow couldn't be added to the comment.
If both light sensors were receives bright light (low resistance) wouldn't there be a short circuit?
I don't think they wld go all the way to 0, but you cld include 2 equal resistors in series with each LDR
that is why they call it photoresistors...I always thought that they either went ON or OFF...
Great 'ible. I just finished my senior project using photoresistors to make an interactive LED table. It also involved some PLC programming for the I/O behaviors. I am entered in a competition tomorrow against my fellow graduating classmates. Here's hoping I win some $$ and get an interview or ten. I learned a great deal about photo cells from personal research and this 'ible explains it pretty clear.
good tutorial!<br/>Did you know that the LED can be used as a photocell?<br/>25 mV with 60 W of lighting small green led<br/>i test it: <a rel="nofollow" href="http://www.youtube.com/watch?v=L3-0aCJOedo">http://www.youtube.com/watch?v=L3-0aCJOedo</a> (only in italian sorry)<br/>
Thank you for this tutorial very informative

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