a circuit equivalent to function generator

[farrokh]

i want to send a AC current with 20kHz frequncy to a coil. I know that It is possible by a function generator. Because function generator is expensise, i want to do by another thing. how can i do it in inexpensive way?

Thanks a lot
Farrokh

 

[BobK]

Oscillator + audio amplifier.

Bob

 

[farrokh]

Oscillator + audio amplifier.

Bob

Thank you for your reply,
I want to use it in metal detector. so it should be light and portable. therefore i think oscillator can't be used, any suggestion?

 

[duke37]

There are many ways of making an oscillator. The simplest I have made uses a CMOS 4093, one resistor and one capacitor. You could also use a blocking oscillator (one transistor and an inductance), a bistable (two transistors) or Wein bridge oscillator (one op-amp).

I am not up to the latest in metal detectors but the early ones used the search coil in an oscillator which varied in frequency and compared this with a fixed frequency oscillator to give a whistle.

 

[BobK]

Or a Colpitts oscillator, which has a single transistor, inductor and a few capacitors and resistors.

Bob