On-Off Switch

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Summary

Introduction

The simple yet robust on-off switch (also called a binary switch or simply a button) is perhaps the most commonly used control component since the development of electronic technology. It is often implemented in experimental instruments such as keyboards and wind controllers to determine whether the user has depressed a key. It should be noted however that pure binary switches are not usually present in acoustic instruments, and so subtleties such as dynamics (in the case of the piano) and half-holing (in the case of wind instruments) are not captured by switches. A notable exception is the harpsichord, in which case each key is in fact a binary switch that triggers an envelope pre-determined by the construction of the instrument.

Switch types & construction

The switch works on the principle of creating or breaking an electrical connection by moving two metals in or out of contact. They can come as normally open (NO) or normally closed (NC).

Output

The most important consideration with the output of a button is constructing a debouncing circuit. When a button is pressed, the metal conductors actually come in and out of contact several times on a micro-scale before settling into a static position. Depending on the use of signal, this can result in strange or noisy attack transients, or be registered as several logical events rather than one. A debouncing circuit compensates for this by allowing current to pass only after contact has been made for a specific amount of time (for instance, 20 ms). Common methods of debouncing:

  • Filter circuit containing a resistor and capacitor in series
  • Schmitt trigger

Devices

External links & references

sensors/on-off_switch.txt · Last modified: 2009/01/25 14:55 by joe
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