60 Hz Noise cancellation 8-bit microcontroller

http://people.ece.cornell.edu/....land/courses/ece4760
60 Hz noise is frustrating for anyone trying to make sensitive measurements of low voltage processes (eg. Electrocardiogram measurements), record audio from electrical instruments (eg. guitar "hum"), or use electronic systems near an AC transformer. The most common way to eliminate the noise is through a 60 Hz notch filter. Because there are inherent variations in the 60 Hz signal, a notch filter is not robust against signal source frequency changes. However, using a microcontroller such as the ATMega32 to monitor a reference signal and output an out-of-phase signal to cancel the noise, we overcome the limitations of a single-frequency selective notch filter and can achieve at least 15 dB cancellation of 60 Hz component in the contaminated signal. Digital Signal Processors (DSPs) or Field Programmable Gate Arrays (FPGAs) can be programmed for this purpose, but are substantially more expensive than the ATMega32.