define(`TITLE', `Very simple metal detector')
define(`DATE', `2014-12-15')
define(`CONTENT', `
The design of the Theremin let my to the idea, that varying the value of the inductivity by approaching some metal should also detune one of two oscillators.
Here, I reuse the design of the oscillator and the mixer from my Theremin and fed the mixed signal into a low pass filter, calculated with Analog's excellent Filter Wizard.
This was btw the first deployment of my new Rigol power supply:
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.
The reference frequency is provided using a generator:
This is the full measurement setup:
I use one oscilloscope to show the varying (yellow) and the reference (blue) frequency, here in the tuned state:
When detuning the test oscillator by approaching some metal to the coil, there varying frequency starts wandering on the screen:
And here are the results:
[gallery columns="2" ids="546,545,544,525,543,528,541,540,535,534"]]]>
')
This was btw the first deployment of my new Rigol power supply:
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.
The reference frequency is provided using a generator:
This is the full measurement setup:
I use one oscilloscope to show the varying (yellow) and the reference (blue) frequency, here in the tuned state:
When detuning the test oscillator by approaching some metal to the coil, there varying frequency starts wandering on the screen:
And here are the results:
[gallery columns="2" ids="546,545,544,525,543,528,541,540,535,534"]]]>
')