TPS

Basic IR proximity sensor
The photo depicts the schematics for an infrared sensor which allows you to detect an object's distance from the robot.

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Torben

It's also quite an effective ambient light sensor.

Note to people who might be looking for a distance finder: this circuit could be used to detect proximity (but needs some modulation to avoid being always "ON" when there is ambient light) but will not actually tell you the distance to the detected object as stated.

Also I wonder if that isn't copyrighted material--it looks like it was scanned out of a textbook.


Torben

HarveyH42

I think it's okay to copy a image or page or so, just not the entire book...

Anyway, the circuit is for line-following robots, where its usually mounted under the robot, and shielded from overhead lighting to some degree...

Torben

Granted.

Exactly. It does not give the distance as stated in the original post.


Torben

allbits

Now its NOT IR, its LIGHT, since it is a photo transistor. If it has to be IR, the LED has to be replaced with IR ones, and the photo - transistor, the one with a response @ lower visible - IR wavelengths.

But just out of curiosity, How good is a photo transistor response to IR??

Torben

What? IR is still light, just not visible light. You can easily buy IR phototransistors and IR LEDs. I'm not sure why you think the schematic wouldn't be referring to IR LEDs and phototransistors, since it's intended for IR?

Excellent, if you use an IR-sensitive phototransistor.


Torben

HarveyH42

Didn't realize there were different symbols for IR LEDs, and regular LEDs... Regardless, the circuit isn't really good for anything where it could pickup light from another source. As for measuring distance... not a chance, not even a good place to start.

allbits

Its just that, when you buy a "phototransistor", will the response curve peak at lower frequencies, close to the IR ones?? Shouldn't it be somewhere in the middle of the spectrum? Or, when somebody buys a photo transistor with a response somewhere in the middle of the spectrum, this wont work, due to ambient light. This could be confusing to the newbies.

And I guess I did miscommunicate with my last post. What I wanted to convey was, to mark the Photo transistor and the LEDs as IR ones, rather than simply writing LED, But I ended up putting it the other way round.

Torben

Depends on which one you buy. Hopefully the buyer is careful enough to check the datasheet and/or specs to ensure they're getting the right phototransistor for the job.

Only if the job is to detect light at those wavelengths.

An IR LED would also need modulation (or really good shielding) to not be affected by ambient light, since ambient light tends to contain a significant IR component. Everyday light contains all sorts of wavelengths you cannot see. Again, it's up to the designer/builder to know what they are doing and buy the correct part.

It says "IR proximity detector" so why would you use anything but an IR LED/phototransistor pair? It's not the purpose of the schematic to point out specifics like that anyway. Many schematics wouldn't even put the word "LED" there--it might just be indicated as "D1" or similar.


Torben