An active noise canceler to eliminate the 60 Hz noise found in electrical signals due to AC power-line contamination.
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.
This project was undertaken during a five-week design lab for ECE 476 with Professor Bruce Land (TA: Adrian Wong) at Cornell University.
Design
Rationale and Source of Project Idea
The original goal of our project was to adaptively cancel sound noise in a rapidly changing environment such as the interior of a vehicle. We were able to find numerous reference papers that had accomplished similar goals. While we have not given up hope that we can cancel audible noise, several factors (eg. poorly functioning microphones, processor speed) have prevented us from achieving this specific goal to date. However, adaptively cancelling audio is a very similar problem to canceling electrical noise.
Early in the semester, our Professor, Bruce Land, suggested making an adaptive noise canceler to help neurobiology researchers who need to make sensitive, noiseless measurements. He had completed some preliminary simulations of adaptive cancellation in Matlab and created a block diagram of a potential solution. We decided to work on this since it would be an excellent first step to the ultimate goal of (sound) noise cancellation.
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fuente : Cornell University
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