Small-Range Motion Detector

This instructable will teach you how to make a small-range motion detector from cheap parts you can get at Radioshack. With this neat project, you can vary the brightness of the detector. This is my first instructable, so please mind the simplicity of the steps. Enjoy!!

Step 1: Materials

For this instructable, you can scavenge for parts at home and/or go to Radioshack and pick them up.


- 1 LED
- Alligator Wires
- Set of Infrared Emitter and Detector (Radioshack #276-0142)
- 1 Small Enclosure/Case (About 3.5"x2.5"x1")
- 2 3V Coin Cells
- 1 PNP Transistor

Step 2: Emitter

There are two parts to this instructable- the emitter and the detector. The emitter is very simple.

Grab the dark LED from the infrared pair- this is the emitter. Pinch the two prongs together, but make sure they don't touch. This will let the coin cell fit firmly. Slide the coin cell between the two prongs. The longer prong should touch the positive side of the battery, and the shorter side should touch the negative side. You can do this all later to save battery power.

Step 3: Detector

This part is the detector circuitry. It is a little more complicated. You can either use breadboard or just work offboard.

Now take the clear LED out of the infrared pair- this is the detector (also called a phototransistor). Connect the negative terminal of the 3V Battery to the negative LED prong using an alligator clip. To make the clip stay on the battery, I used a Neodymium magnet, but you can just tape it. Connect the positive LED lead to the emitter of the PNP transistor. Connect the collector of the transistor to the positive side of the battery. Connect the base of the transistor to the negative detector lead. Then connect the wire coming from the emitter of the PNP transistor to the positive lead of the detector. Now, carefully, put the whole circuit in the small container, leaving the detector easily visible.

Step 4: Using It

To use your homemade motion detector, check all connections, then follow these steps:

First, you lay out the two circuits so that the emitter is directly across from the detector. Leave about an inch gap between them. Swipe your hand through the gap. The LED will blink!! Now, move the emitter back a little more, and swipe your hand again. Keep doing this until you can get a very large gap.


Step 5: Circuit Diagram

This circuit diagram might help you understand the connections.






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    7 Discussions


    3 years ago on Introduction

    Hi everyone,

    One could also use, it runs on the Raspberry Pi and it's also open source.


    6 years ago on Introduction

    Ta DA! Hopefully I uploaded the thing I meant to. A PNP is yes, different than a NPN, but they look absolutely identical. They both have three pins, named from left to right, emitter, collector, base.


    8 years ago on Introduction

    I have a part that does this exact thing, it's called "ON1387" and I dug it out of a dead VCR.


    8 years ago on Step 5

    Thank you so much. I have tried for 10-20 hours to find out how to get these to talk to each other. Even tried 555 chip, built lots of other circuits but none worked. I knew this had to be sorta how to design it but have not done this stuff for 25 yrs.   The trouble I have had since I am so rusty is 1) the positive and neg parts of a circuit diagram hard to tell witch is witch. Label for us new guys :-)    2) you say the neg leg of the photo transistor but they call them C & E.  after carefull studying of your diagram I answered these questions.   I need this circuit to be a no contact switch for a fliud despensing system I am making. Thanks so much!!. doc1tyler  I almost gave up but you saved the day.


    9 years ago on Introduction

    doesnt work, maybe because the circuit is the same as your remote control