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View Full Version : Schematic for "Beam Break" IR sensor for Stamp?



Vern Graner
08-02-2005, 07:22 AM
Does anyone have a quick link to a schematic and part numbers to use for creating an IR "beam break" style sensor for a pin on the stamp? I've been digging around and most of the stuff I come across is designed to detect modulated IR.

I just need to span about 8-12 inch gap and detect when something obscures the beam. I tried using this phototransistor (http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&product%5Fid=276-145) mounted at the end of a black tube (part of a ball point pen cap) to act as a "hood" and used this "high output" IR LED (http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&category%5Fname=CTLG%5F011%5F006%5F002%5F000&product%5Fid=276%2D143) and was not able to get consistent switching using the schematic attached. If someone has a schematic and a part # and a value for the resistor handy, I'd appreciate it!

http://forums.parallax.com/images/smilies/smile.gif

Vern

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Vern Graner CNE/CNA/SSE | "If the network is down, then you're
Senior Systems Engineer | obviously incompetent so why are we
Texas Information Services | paying you? Of course,if the network
http://www.txis.com | is up, then we obviously don't need
Austin Office 512 328-8947 | you, so why are we paying you?" ŠVLG


Post Edited (Vern) : 8/1/2005 11:25:40 PM GMT

Jon Williams
08-02-2005, 07:36 AM
You may not be getting a lot of conduction on your transistor due the current flowing through the IR LED.ˇ You could bump that up, or increase the size of your pull-up so that the junction voltage drops when the phototransistor conducts.

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Jon Williams
Applications Engineer, Parallax

ER-Dr
08-02-2005, 09:29 AM
try
http://www.reconnsworld.com/ir_ultrasonic_basicirdetectemit.html

Vern Graner
08-02-2005, 11:14 AM
ER-Dr said...
try
http://www.reconnsworld.com/ir_ultrasonic_basicirdetectemit.html


Thanx! I bought some new parts today at Rat Shack and will rebuild this circuit using those values and see what I get. COuld just be the parts I had on hand were old/damaged.. We'll see.

http://forums.parallax.com/images/smilies/smile.gif

Vern

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Vern Graner CNE/CNA/SSE | "If the network is down, then you're
Senior Systems Engineer | obviously incompetent so why are we
Texas Information Services | paying you? Of course,if the network
http://www.txis.com | is up, then we obviously don't need
Austin Office 512 328-8947 | you, so why are we paying you?" ŠVLG

Beau Schwabe
08-02-2005, 12:25 PM
Here is a circuit that might be helpful to you that I used for a light pen design.
The idea of this circuit was to amplify the weak peripheral signals. In your case,
just a basic IR amplifier.

... I don't think you will need the last stage of this circuit using the 74HC14.

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Beau Schwabe (mailto:bschwabe@parallax.com)

IC Layout Engineer
Parallax, Inc.

Vern Graner
08-03-2005, 04:00 AM
Short said...
Me again I misdrew the first drawing, This circuit is sensitive and doent care about ambeant light levels. It might be just what you need
Short


Wow! Thats above and beyond! Thanx! http://forums.parallax.com/images/smilies/smile.gif

Vern

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Vern Graner CNE/CNA/SSE | "If the network is down, then you're
Senior Systems Engineer | obviously incompetent so why are we
Texas Information Services | paying you? Of course,if the network
http://www.txis.com | is up, then we obviously don't need
Austin Office 512 328-8947 | you, so why are we paying you?" ŠVLG

Beau Schwabe
08-03-2005, 12:00 PM
Short,

Just an FYI.... You can edit your own posts by clicking on the symbol (upper right) that looks like a pencil.
Likewise you can also 'delete' your own posts by clicking on the "X" symbol.

In Edit mode you can update schematics, text, etc.

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Beau Schwabe (mailto:bschwabe@parallax.com)

IC Layout Engineer
Parallax, Inc.

Don Buczynski
08-03-2005, 10:40 PM
I use a curcuit similar to the initial one described in my projects. It works well over short distances and moderate light conditions. But the emitter LED throws a broad beam like a flash light and it is a challange to get the components lined up properly for optimum distance. A lens on the emitter would help.ˇRadio Shack sells a small plastic card with an IR sensitive patch that glows when in the IR beam.

I came acrossˇthisˇcircuit http://home.cogeco.ca/~rpaisley4/DccBODvt5.htmlˇwhile investigating ways to improve the performance of the IR circuits Iˇuse in my projects. My thought is to replace transistors Q1 and Q2 with the IR detector transistor. The added benefit of this circuit is that it helps to eliminate signal bounce on the input pinˇof the BS2. Currently,ˇthe "one shot" functionality has to be implemented in my BS2 code. I have not yet built this circuit with my intended modification.

This last thought is beyond your requirements statement butˇwhat comes to mind is using garage door opener sensors. http://www.genie-garage-door-openers.com/genie_safe.htmˇ. My garage has a double wide door and the sensors work flawlessly even when in direct sunlight. Not sure what the output of the receiver looks like but it might be interesting to investigate.

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Don Buczynski

http://www.buczynski.com

Short
08-04-2005, 09:59 PM
ˇ Last drawing ,ˇThis circuit works at a great distance and is ok in some light you should be able to use it.

Short