Using IR sensors with BS2
I am working on a project that I need some help with. I am trying to use an IR break-beam circuit to detect when a fruit fly moves across the beam.
Here are some details:
1) The fly is confined to a glass tube within which it will walk back and forth. The tube is not large enough for it to fly.
2) I do not expect the fly to completly break the IR beam but rather "cast a shadow" that can be sensed.
3) I set up the circuit and code similar to what's demonstrated in TestPhotoresistor.bs2 from "What's a Microcontroller", Chp 7.
4) In place of the photoresistor I have an IR detector with a visible light filter (Siemens #SFH205).
5) The IR emitter is from RadioShack, #276-142.
6) When I run the program, the RC Time reading in the Debug terminal remains at 00001 whether something is breaking the beam or not.
If anyone can help me make this work I would be grateful. Thanks.
Sean
Here are some details:
1) The fly is confined to a glass tube within which it will walk back and forth. The tube is not large enough for it to fly.
2) I do not expect the fly to completly break the IR beam but rather "cast a shadow" that can be sensed.
3) I set up the circuit and code similar to what's demonstrated in TestPhotoresistor.bs2 from "What's a Microcontroller", Chp 7.
4) In place of the photoresistor I have an IR detector with a visible light filter (Siemens #SFH205).
5) The IR emitter is from RadioShack, #276-142.
6) When I run the program, the RC Time reading in the Debug terminal remains at 00001 whether something is breaking the beam or not.
If anyone can help me make this work I would be grateful. Thanks.
Sean
Comments
You'll have to use an I-R photo-transistor, with it you may find that the fruit fly presents enough area to result a measurable change in the photo-transistor's collector current.1· You'll want to use the least I-R emission ("intensity") possible.· Then you could use a comparator to·trigger a count/event·(i.e. VCE > x = nothing; VCE < x = fruit fly presence.)
Post Edit -- 1 This will be a subtle variation, requiring some experimentation.
Any chance the fruit flies might avoid I-R (and try to walk backward)?· Like, "Hey, what's that? ·Well, No Way!"
Post Edited (PJ Allen) : 8/20/2006 10:16:36 PM GMT
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-Learn somthing about everything, and Everthing about somthing-
Thanks. I need to ask what the difference is between a detector and a photo-transistor?
As for the fly's sensitivity to IR. IR is used often in fly behavioral monitoring. Research has not uncovered any indication that it affects the fly or that the fly even notices it.
Sean
··An I-R·photo-transistor will/can result an output in proportion to (or as a function of) the incident intensity (irradiance) from an I-R source --·an analog (or variable voltage/current) output.
· An I-R·detector/sensor will turn on/off with the presence or absence of an I-R signal/source (all you can know is that there's enough to turn it on or not enough and it's off.)
· The fruit-fly probably cannot block the I-R source (IRED).· But, now I'm thinking, that maybe you can place the I-R emitter behind a pin-hole that the fruit-fly might be able to block.· Whether enough I-R would get through such a hole to make a difference with a sensor is another matter.· Only experimentation·will tell.
Amaral
What is the OD and ID of the glass tube? How thick is the body of the fly?
What is the slowest and fastest rate that the fly will travel down the tube, in Inch/Sec?
Thanks
DaveG
Photodiode:
http://www.allelectronics.com/cgi-bin/item/PD-2/205/PHOTO_DIODE_.html
Post Edited (originator99) : 8/21/2006 4:28:24 AM GMT
If you modulate the IR and allow yourself to adjust the attenuation of the IR output either mechanical (pin-hole) or electrical (intensity).
With a tuned LC on the receiver that matches the same frequency as the IR transmitters frequency, you can REALLY (100's of times)
magnify the ability to detect something in-between the IR transmitter and IR receiver.
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Beau Schwabe
IC Layout Engineer
Parallax, Inc.
Post Edited (Beau Schwabe (Parallax)) : 8/21/2006 5:39:20 AM GMT
Get the Qprox sensor chip, hook up a small metal plate that sits under the tube, the thicker the better for the metal plate, try various caps to see if one will capture the fly. I have tried experiments with these chips with a metal plate and the right value cap, it will sense my hand at 6 inches away from it, so you may get it to sense the fly with the right cap.
http://www.parallax.com/detail.asp?product_id=604-00038
The thicker the plate, the more sensitive. This chip gives a High out when ot senses something.
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Chris Savage
Parallax Tech Support
csavage@parallax.com
Sean