Pre-Finals Update
Now that our capstone projects have finished up, we have found some more time to work on the metal detector. The prototype coil isn't going to be sufficient for testing the circuits on because it has a different inductance than the final coil, so our current priority is building the final coil.
We modeled the coil housing in SolidWorks and will be 3D printing the final design. Figure 1 shows a model of what the coil housing will look like.
Figure 1: Model of Coil Housing
The receiver coil will be wound around the inner cylinder and the transmitter coil will be wound around the outer surface. The inner cylinder and outer cylinder have a 4 cm and 8 cm diameter, respectively. We do have to keep in mind that this housing will be mounted on some sort of detector shaft.
To speed things up, we will be working on building the oscillator while the coil housing is being printed. The oscillator works independently of the coils so we have the option of building and testing it while the coil is being printed. We chose a Wein-Bridge oscillator for its stability and simplicity, following a guide found here:
Typical VLF detectors operate between 5-100 kHz, so we are going for a target of 10kHz. The circuit diagram and output waveform are shown in Figure 2. The output voltage is the voltage over the rightmost resistor, the one at an angle.
Figure 2: Wein-Bridge oscillator and resulting waveform.
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