Jason and Alon's Coil Corner

In yesterday's update, I mentioned that I would be re-coiling the transmitting coil to boost the output signal of the metal detector. I re-coiled it and found that the change in strength was pretty much non-existent, and after a few experiments I found that the operational amplifier I am using in the Wein-Bridge oscillator is the culprit. The output current is limited to around 50 mA, which doesn't supply enough power to operate the metal detector beyond very close range. I have ordered some new op amps ( OPA 548)  which have a maximum output current of 3A. This should be more than enough to power the oscillator. The new components should arrive early next week.

After much trial and error, an order of jumper wires, and some design tweaking, the VLF metal detector prototype is complete and operational! The biggest challenge was getting the receiving circuit to process the input signal correctly. The size of the coil limited the amount of turns and therefore the sensitivity of the receiving coil, so the received signal is very, very small. I used a simple non-inverting op-amp circuit with a huge gain in order to process the signal. Figure 1  shows the output of the peak detector prior to amplification, and Figure 2  shows the output of the peak detector after amplification.  Figure 1: Transmitted Signal (yellow) and Received Signal  after Peak Detection (blue) Figure 2: Transmitted Signal (yellow) and Received Signal  after Peak Detection & Amplification (blue) There were also changes to the peak detector circuit. With the original integrating peak detector circuit, the output signal did not dro...