Vermes
Advanced Member level 4
This device is based on Atmega8. The main operation which the chip does, is to count impulses. The maximum frequency of Atmega8 is 7MHz, therefore it should be equipped witch a frequency divider. 74LS90 was used with theoretical 10 times divide, which should give 70Mhz of measure, but in practical usage, it gives only 50MHz. The next divider was based on LB3500, it divides by 8 – it works from 30 to 150MHz. To measure high frequencies TFK893 was used (divide by 64, range 70 to 1300MHz). Impulses were formatted by NE592.
Link to original thread (attachment with schema and additional info) – Mikroprocesorowy miernik częstotliwości 1.3 GHz