is this possible or even feasible

[metal mania]

Excellent book inside the metal detector best 25 pound I think I ever spent. The book got me thinking I would like very much to run an idea by you all and would welcome feedback. Ok here goes Im going to design a circuit that oscillates at 1.75khz as say frequency 1 this I would like to follow very quickly with say a 10khz frequency now to my questions.

I had in mind using 2 555 timers when frequency 1 has oscillated for a set period of time it trips a secondary 555 with frequency 2 now is it possible to design a coil with this range of frequency's and also is it best to use two colpitts back to back as it were.

If you know what Im trying to achieve this would mean it is possible many thanks

[Waikiki_Sweep]

Nonresonant coil will work with some range of frequencies and it is easy to build. Check how two frequency (5 and 15 kHz) detector (Fisher CZ) works. CZ5.gif Probably you can just use Fisher coil to test your ideas.

[metal mania]

thanks excellent schematic did u draw it ?

wondered if it was possible to use the 1.75khz as a carrier for the 10khz

[Waikiki_Sweep]

Not my. One very good guy with nickname "jackdetect" has spent 3 month of his life to trace and draw that one of the most complicated metal detector in the world from its PCB in 2004.
Unfortunately Jack passed away at 2006.

[Carl-NC]

The easiest way is to drive a wideband coil with a square wave, then you can change the frequency as often as you like. If you want a sine wave drive, you will need to use a parallel cap for the high frequency and then switch in an additional cap for the low f. This can be tricky to get it right.

- Carl