1
\$\begingroup\$

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.

\$\endgroup\$
1
  • \$\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
    Commented Jul 31, 2014 at 16:03

4 Answers 4

Reset to default
1
\$\begingroup\$

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.

\$\endgroup\$
2
  • \$\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
    Commented Jul 31, 2014 at 12:04
  • 2
    \$\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
    Commented Jul 31, 2014 at 12:20
0
\$\begingroup\$

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.

\$\endgroup\$
1
  • \$\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
    Commented Jul 31, 2014 at 12:06
0
\$\begingroup\$

I think you can use an ultrasonic sensor. If by "motion" you mean human motion, you can use PIR sensors.

\$\endgroup\$
0
\$\begingroup\$

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.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.