38 lines
2.8 KiB
HTML
38 lines
2.8 KiB
HTML
define(`TITLE', `Very simple metal detector')
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define(`DATE', `2014-12-15')
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define(`CONTENT', `
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The design of the <a href="http://a385e-5.de/?s=theremin">Theremin</a> let my to the idea, that varying the value of the inductivity by approaching some metal should also detune one of two oscillators.
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<a href="http://a385e-5.de/wp-content/uploads/20141215123534365a.pdf"><img class="alignnone size-medium wp-image-515" src="http://a385e-5.de/wp-content/uploads/20141215123534365a-300x212.png" alt="20141215123534365a" width="500" /></a>
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Here, I reuse the design of the oscillator and the mixer from my <a href="http://a385e-5.de/?s=theremin">Theremin</a> and fed the mixed signal into a low pass filter, calculated with Analog's excellent <a href="http://www.analog.com/designtools/en/filterwizard/" target="_blank">Filter Wizard</a>.
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<a href="http://a385e5.files.wordpress.com/2014/12/img_2629.jpg"><img class="alignnone size-medium wp-image-532" src="http://a385e-5.de/wp-content/uploads/IMG_2629-300x225.jpg" alt="IMG_2629" width="500" /></a>
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This was btw the first deployment of my new Rigol power supply:
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<a href="http://a385e-5.de/wp-content/uploads/IMG_2615-e1418650869673.jpg"><img class="alignnone size-medium wp-image-521" src="http://a385e-5.de/wp-content/uploads/IMG_2615-e1418650869673-300x225.jpg" alt="IMG_2615" width="300" height="225" /></a>
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The both identical 30V-Max-channels, put in tracking mode, can easily be used as a symmetric power supply, as it is required for the mixer and the filter.
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The reference frequency is provided using a generator:
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<a href="http://a385e5.files.wordpress.com/2014/12/img_2616.jpg"><img class="alignnone size-medium wp-image-549" src="http://a385e-5.de/wp-content/uploads/IMG_2616-300x225.jpg" alt="IMG_2616" width="300" height="225" /></a>
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This is the full measurement setup:
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<a href="http://a385e5.files.wordpress.com/2014/12/img_2630.jpg"><img class="alignnone size-medium wp-image-533" src="http://a385e-5.de/wp-content/uploads/IMG_2630-300x225.jpg" alt="IMG_2630" width="300" height="225" /></a>
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I use one oscilloscope to show the varying (yellow) and the reference (blue) frequency, here in the tuned state:
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<a href="http://a385e5.files.wordpress.com/2014/12/tuned.png"><img class="alignnone size-medium wp-image-518" src="http://a385e-5.de/wp-content/uploads/tuned-300x219.png" alt="tuned" width="300" height="219" /></a>
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When detuning the test oscillator by approaching some metal to the coil, there varying frequency starts wandering on the screen:
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<a href="http://a385e-5.de/wp-content/uploads/detuned.png"><img class="alignnone size-medium wp-image-519" src="http://a385e-5.de/wp-content/uploads/detuned-300x219.png" alt="detuned" width="300" height="219" /></a>
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And here are the results:
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[gallery columns="2" ids="546,545,544,525,543,528,541,540,535,534"]]]>
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