Russian PI metal detector circuit.

Russian PI metal detector circuit.
Classical Russian PI detector where only few components were used working fine
LM555 , TL062 , IRF 740 or 840 . ( IXQT0460P2 in my case)

Contentious tone from speaker but change in tone if metal found 

KIT: 1500 PKR

Testing video click below link

https://www.youtube.com/watch?v=8ApYCEoK97Q