This is one of great project based on AVR microcontroller. It use ATmega 32 as processor and LCD 128×64 pixels for display. If you need to measure low frequency i thought this project, AVR oscilloscope, will be usefull. Maksimum frequency for AVR oscilloscope is 5 kHz (square signal), other signals (sine or triangle) the frequency is lower ( almost 1 kHz) for having clear view of the signal. Voltage input range is 24V AC / 30V DC.
This project use C language and WinAVR as compiler. So, it will be more easy to understand than assembly.