Ibrahim Kamal have developed nice and simple frequency meter which can measure frequencies from 5Hz to 500kHz. Frequency measurement is done by counting timer counts between two same amplitude values of incoming signal. After timer counts are done AT89C52 microcontroller calculates the signal frequency by knowing one timer tick duration.
Result is displayed via four seven segment LED displays that are driven dynamically. Whole PCB and display module is placed in old tester case and used same leads. Author provides full schematic, PCB and source code.