I need to measure alot of different frequencies at the same time (up to 48) How?

[AvionicsMaster1]

You know some of things you think are pretty simple like a farmer planting seeds are indeed quite technical and wireless to boot. Awesome integration of technology with one of the most basic requirements of society. Very interesting project that will make me look at using PICs in different ways. Thanks. I hope you find an answer to your desire.

[pedja089]

I was working on similar project, only difference is that my device monitor 4 seed plates on mechanical planter.
I used 1 IR LED 5mm, and 3 IR photo diode 3mm side by side connected in series, to detect falling seed from seed plate. If there is no detection for 3-5S then alarm will sound. Additional function is to count seed on each row, and total count.
Another idea was to monitor holes on plate and to check if there is seed on every hole.
I didn't use interrupts or counters, just detect falling edge from sensor, count them, and reset alarm timer...
For edge detection I used
IF PinOldState>Pin THEN DETECTED
PinOldState=Pin
That is all.
On my setup time frame for detecting each seed is about 5mS. So just put that in loop, or use timer and interrupt on overflow, set interrupt frequency about 1KHz, and you are done...