The pulse repetition rate can be changed in the settings menu (10 - 200 pps).
For L2 I used a coil from a faulty computer power supply (large "yellow" coil).
I played with the neural network for curve shape discrimination (https://habr.com/ru/post/435884/). In my case, discrimination was only possible for objects the size of a dumbbell or a helmet, so I paused research in this direction.

Hello from Belarus! If you look closely at the circuit of my metal detector, you will notice that there are two grounds in the circuit - GNDA & GNDD, indicated by different icons and not connected to each other ;-) Therefore, there is no short circuit in the circuit. And accordingly, there can be no discussion on this topic :-)
Main page - https://acdc.foxylab.com/node/47 (on russian, use Google Translate). On english - https://hackaday.io/project/167704-foxypi-arduino-nano-metal-detector
Actual schematic - https://acdc.foxylab.com/sites/default/files/FoxyPI_v3_mkII_cir_zoom.png
Current firmware version - 3.8 (see link on https://acdc.foxylab.com/node/47)
This is closed source project.
Since I was doing the project for myself, I did not use a printed circuit board.
Best regards, Alexey

8080/8085 CPU Exerciser from Ian Bartholomew & Frank Cringles successfully completed (screenshot from TV tuner) (see above in description).