Feedback
Feedback is a connection, a loop, between the cause and effect of a process.
Electronic
Sometimes, output from an electronic source affects future input. This can form what is called a "feedback loop". In some cases the output reinforces the input, making it stronger; this is called "self-reinforcing", "positive", "runaway" or "amplifying". In other cases, the output blocks or stops some of the input; this is called a negative feedback loop.
Positive feedback
Think about a sound system with input from a microphone and output to a loudspeaker. If the sound coming out of the loudspeaker is heard by the microphone, a loop is created, from speaker, to the microphone, through the cord, and back into the speaker. The loop is made up of sound and the electrical energy that the microphone and loudspeaker use to create that sound. If nothing stops the sound and electricity in the loop, it will travel faster and faster, which is why feedback starts out as a low hum and turns into a high squeal very quickly
This is an example of a positive feedback loop: the output reinforces the input; it makes the input stronger.
Negative feedback
Think about two mirrors that face each other. The mirrors reflect each other infinitely, or forever, but in each reflection, the image in the mirror is slightly smaller than the image it reflects. The images get smaller and smaller until they are no longer visible. This is an example of a negative feedback loop: the output (the reflection) reduces the input; it makes the input smaller.
The runaway global warming hypothesis
Warm temperature caused a glacier to melt. As the glacier melts, areas that were at one time covered by snow and ice are now water or land. Because snow and ice reflect heat but water and land absorb heat, this causes the glacier to melt faster as more snow and ice is melted. This type of positive feedback is an example of thermal runaway.
Cybernetics
American mathematician Norbert Wiener made feedback loops more well known in 1948 in his book Cybernetics. Cybernetics is the study of feedback loops and their role in communication and control.
Feedback Media
A feedback loop where all outputs of a process are available as causal inputs to that process
Maintaining a desired system performance despite disturbance using negative feedback to reduce system error
An example of a negative feedback loop with goals
A positive feedback loop example
Feedback can give rise to incredibly complex behaviors. The Mandelbrot set (black) within a continuously colored environment is plotted by repeatedly feeding back values through a simple equation and recording the points on the imaginary plane that fail to diverge.
Some effects of global warming can either enhance (positive feedbacks) or inhibit (negative feedbacks) warming. Observations and modeling studies indicate that there is a net positive feedback to Earth's current global warming.
Classical ideal feedback model. The feedback is negative if B < 0.
A popular op-amp relaxation oscillator
A 4-bit ring counter using D-type flip flops
