This noise becomes undesirable when the signal to noise ratio becomes low enough to adversely effect the operation of the electrical circuit. Electrical devices that cause changes in voltage or current are common sources of noise. Noise is often described by how it is coupled in a circuit. The five basic types of couplings are capacitive, inductive, radio frequency, common impedance, and conducted. Of these five the ones that affect the project are capacitive, inductive, and conducted.
Capacitive noise is coupled into a circuit by a capacitive effect.
This occurs when a voltage difference between two conductors is separated by air or other insulating materials. This sepperation creates a capacitor through which noise can be coupled. Inductive noise is coupled into a circuit by an inductive effect and is current based. Current flowing through one circuit induces noise current in another circuit. Conducted noise is coupled into a circuit by the transmission of noise by wires or other conducting materials.