In elektronika.lt and in original pages at sprut.de there is placed simple frequency counter schematics. It consists only from Microchip PIC 16F84 cpu and LCD text module. Author states that this counter is capable metering frequencies from 400Hz to 50MHz. I used faster, 20MHz version of 16F84A-20I/P, and it managed to count 80MHz oscillator output.
It is made on testing breadboard and uncalibrated. I made it just for testing. And the schematics is almost unmodified.
I used small TTL oscilators for testing. These devices are much more precise that cheap quartz crystal used in schematics. It is possible to adjust 10MHz and so you can calibrate your counter. Here is my testing readings- the device is uncalibrated.
|12.000000 MHz||12000112 Hz|
|25.175000 MHz||25175456 Hz|
|28.322000 MHz||28322656 Hz|
|80.000 MHz||79999616 Hz|