This circuit is a stable frequency counter accurate to 5 significant digits. The range is 0 - 30MHz with an input sensitivity of greater then 100mV. The probe connects to the PC serial port.
http://aaroncake.net/circuits/compprobe.asp
This is another project which fullfills a need. I once built a frequency counter using plain TTL chips. That was long before the CMOS HC versions, even before LS was available.
http://www.myplace.nu/avr/countermeasures/index.htm
This is a successor of the PIC16C71 4-digit LED f-counter and V-meter. Some hard to find parts used in the previous version, which are out of production for some time, has been omitted.
http://lea.hamradio.si/~s57nan/ham_radio/fc_led_2/fcl2.html
Imagine you have a radio receiver and you wish to display the receiving frequency. As you know the oscillator in a radio receiver works 455 kHz or 10.7 MHz above the receiving frequency. The 455 kHz and 10.7 MHz difference is called IF Intermediate Frequency).
http://hem.passagen.se/communication/frcpll.html
The device presented here can be used to count events as well as to measure frequencies and times. Most of it is built from discrete HC (high speed CMOS) logic.
http://www.cip.physik.uni-muenchen.de/~wwieser/elec/analysis/FreqCnt/
This circuit is a stable frequency counter accurate to 5 significant digits. The range is 0 - 30MHz with an input sensitivity of greater then 100mV. The probe connects to the PC serial port.
http://www.aaroncake.net/circuits/compprobe.asp