Electromechanical Relays
- Main article: Electromechanical Relays
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Relays have many uses in any event involving electronics, such as Robot Arm or Robo-Cross. An electromechanical relay uses the magnetic field produced by an electrical current flowing through a coil to close one or more mechanical switches.
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Microswitches
- Main article: Microswitches
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Microswitches can open or close a circuit when the lever is actuated. Most microswitches have a single "Power" contact and either one or two other contacts. The other contact(s) can be Normally Open (NO), meaning that a circuit running through that contact is open/off until the switch is activated, or Normally Closed (NC), meaning that a circuit running through that contact is closed/on until the switch is activated.
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Electromagnet
Electromagnets made from iron nails and wire wrappings
Electromagnets are a type of magnet that can be made by wrapping a nail or other iron rod with wire. The magnetic field in electromagnets is created by electric current aligning domains the the wire. The strength of the magnetic field, therefore, can be controlled by the amount of electric current applied.
Microphone
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In years when microprocessors and ICs are allowed, microphones can be easily hacked to react to transfers that produce sound..
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Piezo Buzzer
 Typical piezo buzzer in housing. |
If you need to demonstrate the piezoelectric effect or just generate an annoying sound, piezo buzzers are an easy way to do so. Just apply the required voltage and it will emit a high pitched buzzing sound.
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Magnetic Switch
 Window/Door security magnetic switch |
Magnetic switches can be used to open or close a circuit depending on the presence of a magnet.
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Transformer
 RadioShack 1:1 transformer |
RadioShack sells tiny 1:1 transformers that can be used to power an LED from an audio signal. Follow the wiring diagram on the back of the package and the audio signal, which can be thought of as an AC input in this case, will be converted to DC by the transformer and will power an LED or small relay.
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