The PIC schmidt trigger CCP input is a good FET type input, and you can connect it to most things just using a resistor, and/or through a cap. However the signal needs to be >3.5v or so peak to peak.
Otherwise for small signals it is common to use a single FET to amplify the input wave before going to the PIC pin. Many of the freq meter projects do this, and as Nigel suggested a google search will show you heaps of schematics or good working designs.
The PIC schmidt trigger CCP input is a good FET type input, and you can connect it to most things just using a resistor, and/or through a cap. However the signal needs to be >3.5v or so peak to peak.
Otherwise for small signals it is common to use a single FET to amplify the input wave before going to the PIC pin. Many of the freq meter projects do this, and as Nigel suggested a google search will show you heaps of schematics or good working designs.
ok Nigel but if I feed a square wave clock frequency to my frequency input will it count? Because most of pulse streams on workbenches are square wave not sine waves.Will I still able to measure them with that small front end cap?
Nothing will couple the input to the PIC better than direct coupling when it comes to picking up high frequencies. Just use a 1k resistor and make sure the signal is not higher than 6v.
Now I need more professional details on the signal input.
Whats the minimum voltage level needed on the incoming pulse stream etc......so this amp can amplify the signal to a known signal level that can seen by the micro controller.
The essential points of input processing are to give a high input impedance and to make reading of lower level signals possible, if you have TTL level logic signals then nothing is required and the PIC input itself is fine.
As it's a for a frequency counter it's obviously far more likely, and thus a better assumption that it's for use with more than TTL levels - a further pointer is the requirement for 'safely'.