It just so happens that I own a really nice PIC-EL III. It is
a PIC programmer & development board that Craig
AA0ZZ designed. I thought that I remembered that he might have a simple PIC based
frequency counter design in the manual. A quick little search and presto.

------snip----------

http://cbjohn.com/aa0zz/PIC-EL-III/PIC-EL-III-Manual.pdf

page 11

2.2.8 Signal Conditioner A signal conditioner, shown in Figure 10
is provided to increase small amplitude signals to voltage levels which are detectable
by the PIC. The output amplitude of the DDS Daughtercard is too low to be fed directly
back into a PIC pin for the demonstration of frequency counting. To make this work,
the amplitude is increased by the signal onditioner circuitry. Notice that this conditioner
is not a linear amplifier in that it does not attempt to keep a distortion-free sine-wave
output. For purposes of frequency measurement, a square wave would be just as good
as a sine wave.

Figure 10– Signal Conditioner

Note that header HDR2 is used to select the source of the signal which goes into the
“conditioner”. In one position (jumper from HDR2 pins 1 to 2), the output of the DDS
Daughtercard is fed into the “conditioner” while in another configuration (jumper
from HDR2 pins 3 to 4) a signal from an external source can be brought into the PIC-EL
board via the BNC connector (J7) and routed through the Note that header HDR2 is used
to select the source of the signal which goes into the onditioner”. In one position
(jumper from HDR2 pins 1 to 2), the output of the DDS Daughtercard is fed into the
conditioner” while in another configuration (jumper from HDR2 pins 3 to 4) a signal
from an external source can be brought into the PIC-EL board via the BNC connector
(J7) and routed through the “conditioner” before going to the PIC. (Another option
is to route the DDS output directly to the BNC, bypassing the “conditioner”, by installing
a jumper between HDR2 pins 2 and 3.) The sensitivity of the signal conditioner on
the PIC-EL III is about 100 mv P-P at 7 MHz.

------snip----------

I have not done much work with the board since I assembled it recently. (Lot of projects
on the bench these days.) This might be an excuse to pull out the board and see if
I can get it running as a simple freq counter. Maybe this can be scaled to work with
the RF power meter project that I am researching.