I'm following the info on http://www.rfcandy.biz/communication/imp_lc.html to build an LC Meter. I have the basic design down and my pic16F690 is reading and displaying both frequencies. My problem is with the math. I need to calculate the formula,

L = 1/(C*(2Pi)^2) * (1/f2^2 - 1/f1^2)

Where the C value is in the pico farads, f is in Mhz and L is in uH. The pic16 doesn't seem to do so well with this calculation. So I need a variable with 18 decimal places?? 2^32 isn't enough. What can I do to get this calculation?

 

If you are using assembler, download AN526, AN544, AN617 and AN660 from the microchip site. The precision of these routines could be extended with a bit of headscratching. It is also possible that you could scale some of the variables ie:
if c = 0.0000023
you could replace it with 23 but instead of doing 1/(C*..............) do 1000000/(C....

The chap is only charging 25 euros for a programmed chip which sounds good value.