i wish to design a guitar tuner using pic16f84, got 3 led to indicate the frequency whether they are too high, low or ok. but i got some question about how to write the code. let say a=100hz, b=200hz, but if input frequency is 150hz, so should i light on the high led or low led? because if he is plucking A string, then should light on high led, but if he is plucking B string, then light on low led.so how should i determine?

 

You would either need a switch to tell the PIC what string it is or assume that the guitar is not too far out of tune and anything closer to a than b is string a. At the exact midpoint (fairly unlikely) it would be a cointoss.

 

thanks for your reply. i know can count the frequency of the signal by using tmr0 of pic16f84, but i don't know how to start. can you guide me? or show me some code to begin with..thanks in advance.

 

Have a look here

http://www.microchip.com/forums/tm.aspx?m=406805&mpage=1&key=tuner,guitar&#407208

Buena suerte.

 

Have a look at this:
http://www.qsl.net/yo5ofh/pic/frequency_meter_with_pic_16.htm
A lot of the code will be unnecessary for your project but might be a good starting point.
The circuit for yours will probably have to be different to include filters, etc.