Frequency counters are very popular and easy to build projects. This one is a AT90S8515 microcontroller and Lattice ispLSI2032 PLD based frequency counter. While microcontroller mainly takes care of communicating and data display, PLD counts incoming pulses and scales them down because of hardware 36bit counter implemented. When counter counts up - it generates an interrupt for MCU.

Frequency counter has 5 operating modes:

• Mode 0: Frequency(IN-1), up to 2.4GHz (in resolution of 100Hz);
• Mode 1: Frequency(IN-2), up to 100MHz (in resolution of 1Hz);
• Mode 2: Frequency(IN-2), up to 10kHz (in resolution of 100µHz);
• Mode 3: Pulse Period(IN-2), up to 10sec (in resolution of 100nsec);
• Mode 4: Pulse Width(IN-2) up to 10sec (in resolution of 100nsec)

And have three dedicated inputs for various cases:

• IN-1: ZIN = 50ohm, 10MHz-2.4GHz;
• IN-2(AC): ZIN = 1Mohm, 10Hz-100MHz;
• IN-2(TTL): DC-100MHz

Frequency counter also has ability to communicate with PC via serial port. This way counter can log data to computer or be simply controlled by computer. Project files and source codes are available for download in project page.