Circuit - IR sensor to read at <3cm distance (+10points)

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koolslash

Joined: 24 May 2009
Posts: 26

20 Jun 2009 9:41 ir distance sensor circuit

I want to make the IR receiver highly sensitive that i could detect the IR light across the DC motor DISC. it will have to generate a pulse when a cycle is completed.

+10points will be awarded to a person who provide early exact solution.
i need it to implement and show on this Monday.

banjo

Joined: 24 Dec 2005
Posts: 644
Helped: 118

20 Jun 2009 16:59 infrared sensor cricuit

What you are looking for is a photointerrupter type circuit. There are a number of these from various manufacturers. Basically, they consist of an IR LED and a phototransistor mounted in the same package. This insures that they are always pointing at the same spot.
Operation is simple. Run DC current through the LED to produce a constant IR beam. When the beam hits a reflective surface, the reflected IR will saturate the phototransistor.
Below is a link to a sample part. While this part requires mounting on the edge of the disk, there are plenty of others that can work totally reflective.
http://www.ic-on-line.cn/IOL/viewpdf/TLP814_291117.htm

For a Monday demo, you are going to have problems getting parts. However, this type of photointerrupter is the favorite method of detecting reel motion in VCRs. If you have an old junk VCR, remove the reel hub and you will find this chip under them. Look at the underside of the reel hub and you will see the refective pattern that is triggering the sensor.