Distance Sensor Selection

I am looking for a distance sensor emitter/receiver pair with a range of about one foot. Reflective sensors, such as those offered by sharp,
will not work for my application, as I need to be able to detect the distance to a specific point, as opposed to the distance to any surface. This device will be used to let a small autonomous robot know when it is getting close to, and reaches, its destination. In getting to its destination, it has to navigate an obstacle course with several walls, thus the reason a reflective sensor would not work- it would be unable to distinguish between the destination, and just another wall on the course. Can anyone give me some ideas as to where I might find such a sensor? Thanks.
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I haven't done this yet, but I've read about it... Your target transmits pulses via infrared (or RF) as well as ultrasonic. The robot is capable of receiving both. When the robot receives the IR of RF pulse, it measures the time until the ultrasonic pulse arrives. Multiply that time by the speed of sound and you get the distance to the sensor (with some small error).
Your obstacle course may prevent this from working.
BRW
wrote:

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Sounds interesting. The obstacle course shouldn't be a problem, as over the distance I need this to work (about a foot) the course will be clear. I'll have to look into that. Any chance you could give me links to more information, such as circuit diagrams, or sensor selection information? I would like something simpler, both because of space limitations and my skill level, preferably along the lines of a single sensor that outputs a voltage proportionate to the distance between it and the emitter, but this idea definitely has merit. Thanks.
Bennet Williams <> wrote in message

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Sorry. It's been awhile since I looked at it, and I don't seem to have any web links. But there is info out there.
Digi-key and/or Newark sells everything you need. I'm afraid my idea for implementation was not simple (none of my ideas ever are). However, I was thinking in terms of triangulation to determine the robots position. Your case is much simpler.
I'm not aware of any pre-packaged emitter/sensor pairs that give this functionality. I thought I would build a little "beacon" tower with the multiple IR transmitters and U/S transmitters. A PIC would control these. Likewise on the robot end, multiple IR and U/S receivers would be monitored by a PIC. But the U/S sensor cannot be monitored directly. I had found a circuit diagram for the U/S receiver electronics.
BRW
On 8 Oct 2004 09:46:15 -0700, snipped-for-privacy@gmail.com (Macavenger) wrote:

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Ok, I think I have found a potential solution, but I need a little help with some details. For the purposes of navigation, I have set up at the destination point a Pololu IR beacon that outputs a modulated IR signal at 56.9 kHz. With a detector designed to detect signals at that same frequency, It would appear that I could determine the distance by looking at the output of said detector. There are, however, two issues I would need to deal with.
1) The output fluctuates fairly widely even at a set distance. At the range I want to start detecting the signal, the output of said detector varies between 3.50-3.60 Volts, while at the range I want to consider my robot as having arrived, it varies between 3.40-3.50 Volts. This can be easily solved with an averaging filter of some kind. My question for you folks is where might I find an IC that performs that function?
2) The range of variation over the distances of interest is probably large enough to be able to detect, even with the fluctuation in readings ( 100 mV) However it is still fairly small, and it might be nice to amplify it somewhat to achieve better resolution. How might I accomplish this-Just run the signal through a run-of-the-mill op-amp? The detector outputs a high voltage, decreasing as the input gets stronger, so I would think the signal might need to be inverted first (inverting amp?) I have a basic understanding of amplifiers, however it is VERY basic, so circuit diagrams would be appreciated.
Thank you for any assistance you may be able to provide. The simpler the better. Thanks.

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