View single post by Slider2732
 Posted: Mar 12th, 2008 05:32 PM
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Slider2732

 

Joined: Mar 3rd, 2008
Location: Muskogee, Oklahoma USA
Posts: 349
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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 !

:biggrin: