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Need help with advanced proximity sensor

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Need help with advanced proximity sensor

Postby Murpocalypse » Sat Mar 21, 2015 5:00 pm

Hi, I am working on several small bots intended to work together, and I wish to equip them with proximity sensors. I know how to build simple sensors, but this project requires something more sophisticated. First, they need a range of at least a couple of feet, and the ability to adjust the trigger distance. Second, they need a narrow field of view, only a few degrees directly in front of the sensor. Third, they need to be modulated (or something) so that they cannot be triggered by anything but their own, individual signal. Fourth, I need a bunch of them, so it would be nice if they were (relatively) cheap, compact, and easy to build. All that is asking a lot, I know, and I confess I am stumped. Does anyone have any ideas?
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Re: Need help with advanced proximity sensor

Postby pebe » Thu Mar 26, 2015 11:32 am

That's an interesting task. Probably the easiest sensor would be an IR sensor within the back end of a tube to give directionality.

But the problem would be making an omnidirectional IR transmitter if were needed, so details of the transmitter requirements would be helpful.
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Re: Need help with advanced proximity sensor

Postby Murpocalypse » Fri Mar 27, 2015 7:06 pm

What do you mean by "transmitter requirements"? I do not need to transmit information, just read the distance to an object, and provide a signal when the target distance is reached. Preferably, the distance could be set by a small potentiometer from 0 to 2 or 3 feet
As far as directionality goes, I had thought of using an IR laser as the sending part, and IR detector(s) as the receiver. Perhaps a LED in a tube would do as well, and would certainly be cheaper.
I spoke of modulation in my original post because I am looking for a way to make each detector unique, in that it cannot be triggered by stray signals from other detectors, or ambient IR.
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Re: Need help with advanced proximity sensor

Postby pebe » Sat Mar 28, 2015 12:11 pm

Murpocalypse wrote:What do you mean by "transmitter requirements"? I do not need to transmit information, just read the distance to an object, and provide a signal when the target distance is reached. Preferably, the distance could be set by a small potentiometer from 0 to 2 or 3 feet
As far as directionality goes, I had thought of using an IR laser as the sending part, and IR detector(s) as the receiver. Perhaps a LED in a tube would do as well, and would certainly be cheaper.
I spoke of modulation in my original post because I am looking for a way to make each detector unique, in that it cannot be triggered by stray signals from other detectors, or ambient IR.

I am not sure whether you intend using a communal transmitter for all the 'bots', in which case you will need an omnidirectional one, or an individual transmitter for each bot (with different transmitters located in different places. Or whether each bot will have its own transmitter/receiver setup so that it works on a reflected signal. Which is it?
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Re: Need help with advanced proximity sensor

Postby Murpocalypse » Tue Mar 31, 2015 8:50 pm

Each bot is completely independent, as far as sensors go, and each sensor is an individual, operating on it's own unique, reflected signal. Sorry I have done such a poor job of explaining what I am trying to do. posting.php?mode=reply&f=1&t=6333&sid=32f9c141d33c21bc11bf57e8723fe318#:oops: :oops:
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Re: Need help with advanced proximity sensor

Postby pebe » Wed Apr 01, 2015 12:42 pm

Hi Murpocalypse,
Thinking more about your needs, you could use either infrared or ultrasonic methods. Here is an ultrasonic detector circuit that would probably be suitable:

http://circuit-electronic-models.blogsp ... ector.html

Alternatively, you could use these inexpensive modules.

http://www.ebay.co.uk/itm/High-Accuracy ... =undefined

If you have got lots of bots, then:-

http://www.ebay.co.uk/itm/1-2-5-10X-Ult ... 4184f4c0f4

If you choose to use IR, then you could use the sensor in a tube as I suggested earlier. The IR emitter could be fitted outside the tube, and facing the same direction, so that its IR signal was reflected into the tube.

The datasheet for the TROP2438 sensor states that its range is 35m when used with a TRAL6200 emitter driven at 38kHz at 250mA. That should still give a significant reflected signal, so you could reduce the current to give the range you want. To save battery current in your bot, you could pulse the emitter with, say, 12cycles of 38kHz every 10 or 15 secs.

The sensor comes complete with its amplifier and detector. You could use a 555 wired as an astable oscillator at 38kHz; there are plenty of circuits available. Or if you are using a micro controller then possibly you could program it to give this extra function.

My preference would be for the Ultrasonic modules.
Hope that helps.
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