design of metal detector using tiny13

hi i am designing metal detector using avr tiny13.
i m planning to use 555 ic to energize the coil and giving this output to tiny13 at pin2(clk1). i want to know that is it possible to generate squre wave using tiny13 so that i can remove 555 ic from my circuit.also how can i blink leds after detecting metal using SPI or any other method?
please reply imigiatly.

actually i done 1 correction.I removed 555 ic part
now i am thinking to generate squre wave(25Khz,1.6V)to energize the coil form any one i/o pin of tiny13.So my first question is hw to generate this squre wave?for that purpose i m thinking to sellect internal osclillator of 128Khz and using CLKPR(clock presceler register)i can generate 25Khz freq.and for amplitude adjstment i m using Non-inverting amplifier.
so how i can design non-inverting amplifier which wil give 1.6V at output?
this input i m giving to the coil and output of coil giving to pin2(clk1).
when metal wil be near to the coil then the amplitude of the wave changes and led blinks at output side.
so my major question is how controller can detect this change in megnatude of the squre wave?
please reply fast.

Try reading **broken link removed**. It's by a contributor here and contains some very good information about the design of a PI metal detector.

Mike.

thanks pommie i saw this page and got ideas about selection of coil,design techniques and different types of existing metal detectors.
actually i want to design hand held metal detector .its circuit should be so small,compact and effective,thats why i selected tiny13(8 pin 8 bit) please tel me some good sites of designi hahd held metal detector,i m waiting for reply.