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I have to design a circuit for a device to detect any motion in front of the device up to 2 meters. I have tried with IR reflection sensor, but couldn't achieve the range. Then, I found a circuit on the internet which works on passive detection of shadows.

So, basically it takes in the ambient light, and when there is a obstacle in front of the sensor, output is triggered. As mentioned in the circuit about using L14F1 as sensor, I could not get that part where I am living. So, I used a a normal phototransistor with some black shielding around it. It seems to be working up to 40 cm.

  1. Which type of sensor should I look for? What are the specifications that I need to look for this application (detect fast change in light up to 2 meters with narrow detection)?

  2. My major problem is I do not know if this circuit works properly for fast light changes. I need to drive a DC motor at output for 5 sec whenever the sensor detects a movement up to 2 meters.

  3. Is there any other kind of low-cost and effective sensor or method for this kind of application?

I am a beginner to this field. I am willing to learn by doing. So, any suggestions and advice is greatly appreciated.

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  • \$\begingroup\$ The response of the transistor and the Op-Amp is very quick. The only "slow" aspect of this circuit is going to be the time-constant (51 seconds) designed for the output of the 555 timer. \$\endgroup\$ – sherrellbc Jul 31 '14 at 16:03
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Maybe you can rig a standard motion-activated light to work for you: add a lens or pipe in front of it so it looks only at the point you are interested in?

They work with a PIR sensor and a Fresnel lens, which focusses alternate parts of the field-of-interest on and off the sensor, so a movement from an 'on' part to and 'off' part or vice versa gives a large chance.

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  • \$\begingroup\$ I just need to trigger an output when someone passes by the device. I have thought of PIR sensor before. But,I think PIR sensor would be expensive and also it has a wide angle of detection or??. how could i build a low cost detection circuit like the one used in this device tronixstuff.com/tag/glade I want to build a similar device. So, it would be helpful if someone could suggest me a better option for this application \$\endgroup\$ – tony Jul 31 '14 at 12:04
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    \$\begingroup\$ I can buy a motion-triggerd lamp in any hardware store for a few Euro's. If you consider that expensive.... As I suggested, the wide angle of detection can be reduced by a pipe and/or lens. \$\endgroup\$ – Wouter van Ooijen Jul 31 '14 at 12:20
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What exactly does "any motion" mean? What is moving, and how much motion constitutes a "trigger"?

Since your comments indicate that you can work with ambient light, a cheap USB camera and some software (such as OpenCV, but that may be overkill) can be a remarkably effective solution.

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  • \$\begingroup\$ I meant any movement in front of the device. like if a person passes by within a range of 2 metres. I think it would be expensive . I need a low cost solution \$\endgroup\$ – tony Jul 31 '14 at 12:06
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I think you can use an ultrasonic sensor. If by "motion" you mean human motion, you can use PIR sensors.

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Elecfreaks PIR ($3) and Amazon PIR ($6)

I've used these PIR sensors in a few projects. They are cheap, reliable, and easy to hook up. As Wouter van Ooijen says in another answer, if you want to narrow the field of view use a cardboard tube.

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