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Old 3rd December 2007, 07:38 PM   #1
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Default On/Off sensor with LEDs

Hello,

I am pretty new to experimenting with electronics, and am wondering if someone can point me in the right direction.

My idea is to have the following:

Two pieces of plex or glass parallel to each other, an LED on one side and a sensor on the other side. Have objects travelling about between the two panes, and when an object passes between the LED and the sensor, it will trigger it. Ultimately the goal is to generate MIDI data with an array of sensors. Any ideas what kind of sensor to use? Is LED a good way to acheive something like this?
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Old 3rd December 2007, 08:52 PM   #2
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The Sharp IS471FE is a photodetector/demodulator with on-board synchronous modulator and LED driver for this sort of app. Get them at digi-key for $2.72 ea. along with a 940 nm IR LED for another $0.27 or so. I have tested it and range is at least 6 feet, probably more.

Modulation makes detector immune to ambient light and to other, nearby emitter/detector pairs. Logic level output is low when beam from LED is received, goes high when interrupted. Response time is about 400 us.

I_F
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Old 3rd December 2007, 11:17 PM   #3
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If you only need very short range and want to use a lot of sensors, the IC might be too expensive. In that case you can probbaly make do with with much cheaper phototransistors and matching wavelength IR LEDs. However, if you want to put them close together you may have problems with the LEDs illuminating more than one sensor. That problem can be solved by scanning the LED/detector pairs with a microcontroller. It all depends on how much work you're willing to do and on what you want the device to be able to do.

I_F
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Old 4th December 2007, 07:14 AM   #4
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Thank you for the replies. Indeed the range I need is very small, about 2cm. But the sensors will not need to be too close too each other, probably about a 10cm radius of space around each one. I'm just learning the basics of electronics and circuitry right now, so I am a long way off from being able to integrate this stuff, but I just needed to know if I was starting in the right direction.
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Old 4th December 2007, 07:52 AM   #5
Nordic is offline Nordic  South Africa
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Look around a bit on google... you could use a PIC and let the led be a sensor as well...
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Old 21st December 2007, 05:13 PM   #6
larzman is offline larzman  United States
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Interesting application. I used to work as a Product Manager for Photomicrosensors at Omron. They make several models that will fill your need of close proximity sensing. You should be able to use a non-amplified (thus much less expensive) model with appropriate detection circuitry. The Omron Photomicrosensor Catalog has numerous application circuits that are extremely helpful in developing your specific circuit.

From past experience, they make very reliable, close tolerance photomicrosensors, commonly used in Xerox and Lexmark printers, mice, etc.
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Old 21st December 2007, 11:47 PM   #7
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Check out the laser harp here:
http://www.cibomahto.com/?s=laser+harp
Scroll down the page. Matt brought the latest version to the last Phoenix DIY meeting and it is now in a wood frame about 4' tall and 5' long. He uses laser pointer lasers and CDS photocells. There is a PIC18 uC that controls it and communicates with a PC via a USB (or was it serial port?).

I_F
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