# Line Noise

![ A noisy power supply signal caused by a running motor.](https://phabricator.purduesigbots.com/file/data/ay5mibti56thhgp53m76/PHID-FILE-47i334uvtbaky6svgfbq/electrical_line_noise.jpg)

Some noise is generally unavoidable, but many sources of significant noise can be identified and isolated. It is also possible to reduce noise when processing a signal using Fourier analysis.

Noise from a seemingly unimportant signal can be emitted through the generation of electromagnetic waves, which can induce fluctuations in nearly sensitive signals. Analog sensors and other sensitive electronics are the most vulnerable inputs to noise; digital signals are more tolerant due to the use of a Schmitt trigger on most digital inputs.

Noise generally only affects the perceived amplitude of a signal. For random fluctuations in a signal's frequency, the term [jitter](https://wiki.purduesigbots.com/electronics/general/jitter) is usually used instead.

## Thermal noise

Heat is by definition the thermal energy of atoms moving about, and the kinetic energy of these atoms is generally not uniform. Since a VEX robot cannot operate near absolute zero, thermal noise is present in all signals and has a roughly uniform distribution across all frequencies. However, the magnitude of such noise is generally insignificant, ranging from 10 nanovolts to 1 microvolt in amplitude.

## Switching noise

Switching noise is generated by the circuits inside controllers such as the [V5 Brain](https://wiki.purduesigbots.com/vex-electronics/vex-electronics/vex-v5-brain) turning on and off. Since most External Processors operate at very high clock speeds, typically in the megahertz range, noise of this frequency is generally outside of the intended frequency domain and can be filtered using a decoupling capacitor. Switching noise generally appears on the power supply voltage and occasionally in low-frequency output signals.

Switching noise is also generated by switch-mode power supplies, such as the voltage regulators on the [PandaBoard](https://wiki.purduesigbots.com/electronics/general/external-boards/pandaboard). Once again, the noise frequency is typically very high and is filtered at the power supply's output.

## ADC noise

When sampling an analog signal using an [analog-to-digital converter](https://wiki.purduesigbots.com/electronics/general/analog-digital-converter), or ADC, noise on the order of one bit of precision [(ref)](http://en.wikipedia.org/wiki/Quantization_error) (typically 1 to 10 millivolts) is typically introduced.

Some processors go to sleep while sampling analog inputs, reducing the impact of switching noise on analog input values.

### Teams Contributed to this Article:

* [BLRS](https://purduesigbots.com/) (Purdue SIGBots)


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