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Movement Detection of an object in short range

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Akhil Mohan

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May 13, 2011
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The IR transmitter and receiver circuit attached in the file is not working properly. I don't know how to get a good result to detect movement. From the web, I came to know that photo transistor output is much better than photo diode, so I bought a l14g2 photo transistor (3 leg), I am also trying with that.

Please inform me a good method to detect movement of a object (with either photo diode or photo transistor)

Thanks in advance :)

It may be Photo transistor, diode, LDR, PIR, ultrasonic or any other sensor. All are meant for the purpose they are built for. It all depends how you impliment and make them work with your talent, skill and knowledge in the field. Anyways, no attachments are found in your post.

1. There's no file
2. What's the intended detection method? Change of reflection or transmission?
3. What are the object's size, distance, surface propererties, speed and direction of movement?
4. How about enviromental light, interfering objects?

Sorry for the mistake.

What I am trying to do is to detect movement of a human being using IR Tx and Rx. IR Led continuously transmits radiations and which will fall on the Rx (either photo diode or photo transistor). When the subject comes in between Tx and Rx the change in output is detected and used to trigger the PIC micro controller.
There will be ambient light and it will also affect my output and next stage of the project will be the removal of noise.

I think this time this is much clear:)


  • TX and Rx.bmp
    299.6 KB · Views: 68

When the subject comes in between Tx and Rx the change in output is detected
Sounds light you are using light barrier rather than light reflection principle? I also expect a Tx/Rx distance > 1 m. In this case, optics (lenses) or modulated Tx and sensitive amplifiers are needed. Plain IR LED and phototransistor will hardly give a detectable DC signal at larger distance. They are good for a few cm distance.

You need something like these circuits
and for longer distance add optics to transmitter and receiver.

Infrared alarm barrier

**broken link removed**

**broken link removed**

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Regards KAK
i did a project once to count the number of people entering and leaving a room once. i just used ldr and laser. place the ldr inside a pen cap or some place where only a direct beam of light can reach.

hope this helps.
I got relatively a stable output by the attached circuit. Next I am trying to avoid the noise
Suggestions are expected


  • Tx and Rx New.bmp
    360.2 KB · Views: 52

Did you try ultrasonics as they can give good results for small distances about: 3m

I want it to be a low cost one, and initially I thought use of ultrasound may increase my budget. I will check the prize in the shop and consider your suggestion.

Strictly spoken, there's a difference in detection principle. A light barrier is not exactly detecting movement, only objects that are crossing the light beam. But it's the most rugged method for just this purpose. Ultrasonic distance measurement or doppler offers a chance to detect other kinds of movement. But's it's rather sensitive to enviromental conditions, e.g. air movement. The ultimate techniques, not affected by these problems are laser TOF speed sensors, 3D scanners and image processing. All these are used in industrial safety systems, where reliability matters.

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