Improving Freq Counter Input Sensitivity?

[Mike - K8LH]

Hi guys:

Can anyone recommend a better input circuit for my home brew Frequency Counter please? This input circuit, borrowed from the Internet, needs about 400-mv at low frequencies to 800-mv or more at the higher frequencies... I'd like something a little more sensitive, not too complex, not too many parts, and, what about input over voltage protection (a pair of back-to-back 1N914s perhaps?)?

Thank you for you time and kind consideration guys...

Regards, Mike

 

[Nigel Goodwin]

You might try the preamp from

**broken link removed**

, or try searching for the Weeder Technology frequency counter, an LCD version of the original MicroChip application note - that uses an FET input as well. Weeder no longer sell the kit, and if you can't find the circuit I have it at home somewhere.

 

[Roff]

I simulated this, but I haven't built it. It works in simulation (into a 5pF load, not shown) from below 100Hz to above 10Mhz with input amplitudes from 100mv p-p to 20v p-p. A Schmitt trigger on the output would be a useful addition, if your PIC input doesn't already have one.
You can easily extend the low end limit by making C1 and C2 larger.

 

[Mike - K8LH]

Hi Nigel & Ron...

Thanks for the replies...

Nigel, I've come across the Weeder schematic before... Thank you...

Ron, thanks for the example...

Regards, Mike