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ITC Bridge > Ask a Question, Give an Answer > Opinions, advice, techniques, software, and methodology > Built proximity sensor |
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ITC Bridge > Ask a Question, Give an Answer > Opinions, advice, techniques, software, and methodology > Built proximity sensor |
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| Built proximity sensor | Rate Topic |
| Author | Post |
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| Posted: Mar 12th, 2008 05:32 PM |
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1st Post |
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Slider2732 Member
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An oddball circuit, but possibly of use. I started off with the second circuit on this page: http://www.z80.info/uexosc.htm It is designed to oscillate from an X-tal and thoughts were that perhaps it might give a white noise source. This seemed to work, on connecting an LED to the output. So I went about making the output audible. I replaced the 100N capacitor with a 10K trim pot. Then, by trial and error added or subtracted capacitors and whatnot. The biggest change was the introduction of the MPF102 field effect transistor, which gives the sensing of body movement. The result, is a proximity detector that has a useful range of a couple of feet, from very few components. The note rises and falls with a move toward or away from the circuit and an LED lights, relative to distance. In fact, just for fun, my wife and I played a daft game. The idea was to create a wolf whistle hehe. Lots of jumping forward and back and from side to side ensued. The circuit is below and please excuse any errors, it's only the second one i've drawn. The output from 4.5V (where the circuit seems most stable) is enough to drive a 0.5W speaker at a decent comfortable volume.  Components: X1 - X-tal rated at 6 MHz R1 - 100 ohm R2 - 330 ohm R3 - 330 ohm C1 - 10uF L1 - LED D1 - general diode D2 - general diode T1 - MPF102 and the DM7404N chip isn't quite so huge in reality ! 
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