Easy, Simple Dark Detector

Introduction: Easy, Simple Dark Detector

Hello! Today, you will be building a Dark Detector. It's easy, simple, and really cool. I got the idea from a magazine and made it my own. This is my first instructable, so I hope you like it!

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Step 1: The Parts

For this instructable, you will need:

  1. 2n3904 NPN transistor (1)
  2. LED (1)
  3. Breadboard (1)
  4. Jumper wires (2)
  5. 9-volt battery with snap connector (1)
  6. photoresistor (1)
  7. 100k ohm resistor (1)
  8. 470 ohm resistor (1)

Step 2: Assembly

If you follow the pictures, it should be pretty easy to build. There are a couple of notes you should always remember when building circuits.

  • The longer lead of the LED is called the anode, and it is positive and the shorter one, the cathode, is negative.
  • Red Wire=Positive and Black Wire=negative
  • Always remember EBC for many bipolar transistors. Make sure the bulge goes the right way.

So, here are the actual steps.

  1. Connect the power as shown in the picture.
  2. Insert both resistors into the positive bus of the breadboard. That is to say, insert the resistors into the top bus. use the picture for help.
  3. Insert the LED anode across the 470 ohm resistor and insert the cathode in the space between the other 100k ohm resistor. Use picture for guidance.
  4. Insert the transistor. I don't think the picture does much good in this instance, so follow these instructions. Insert the collector across the cathode of the LED and the base across the 100k ohm resistor. The emitter goes one slot over from the 100k resistor.
  5. Now insert the photoresistor across the emitter and base of the transistor.The picture is useful.
  6. Finally, use the picture to run the negative lead into the emitter of the transistor.
  7. Flip the switch and enjoy!
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    5 years ago

    Awesome instructable young sir! Dark detectors are fun little projects. Check out an op amp (/ comparator) dark detector, pretty cool aswell.

    Ps. Word to the wise ; always check data sheets for the pinout for your "bipolar transistors" (any component for that matter). EBC is pretty common for NPN Bipolar Junction Transistors, but by no means is it regular enough to assume "Emmiter Base Collector" for all your BJTs.

    Kudos on a cool project.