Sound, Light, Motors, Miscellaneous

This section describes schematic symbols for sound devices, lights, motors, and miscellaneous. CLICK HERE IF YOU CAME FROM A WEB SEARCH

Relay
A relay is an electromagnetic switch. Applying current causes the electromagnet to become active and pull the contacts together. On the schematic, the electromagnet is the part of the symbol that looks like half a transformer or inductor. The contacts are right beside (or above or below) the coil. These contacts can take on any of the normal switch configurations. Pictured here is a simple SPST (or Single Pole Single Throw) relay. This means the the Relay contains one set of contacts and can only be switched one way (on or off). Other types of relays include SPDT (Single Pole Double Throw-A relay with one contact that can be toggled both ways), DPST (Double Pole Single Throw-A relay with two contacts that can only be on or off) and DPDT (Double Pole Double Throw-A relay with two contacts that can be toggled both ways).

Dynamic Microphone
A microphone is a device that translates sound waves into varying electrical current. A dynamic microphone is a microphone that uses a small coild moved through a magnetic field to generate a voltage that varies as the sound varies. The coil is attached to a small diaphram, which vibrates with the sound waves.

Condenser Microphone
A microphone is a device that translates sound waves into varying electrical current. A condenser microhone consists of a diaphram that changes the distance between two plates. This causes a change in capacitance proportional to the sound waves.

Electret Microphone
A microphone is a device that translates sound waves into varying electrical current. An electret micrphone is a dynamic microphone that contrans a small transistor amplifier. Thus, it needs current to run. There are three connections on an electret microphone: the power, signal and ground. The power connection is the connection sticking out of the top of the symbol. Often it is marked with a +. The signal is the line in between the two other lines. Those two other lines are the ground and also the shield, which helps minimize interference.

Piezoelectric Buzzer
A piezoelectric buzzer contains a small crystal that produces a sound when current is applied. A small circuit alternates the current on and off, thus causing the crystal to buzz.

Speaker/Earphone
A speake is a device that translates electrical variations in current into sound waves. Most speakers use a coil that sits in a magnetic field. Changing the current through the coil causes it to move. This movement is transferred to a large cone which further amplifies the sound. An earphone is simply a very small speaker that sits in your ear.

Incandescent Lamp
An incandescent lamp produces light through heat. It does this by heating a wire filiment by passing a current through it. This filiment sits inside a glass bulb that contains no air. The vacume prevents it from just buring up or melting. The very hot filiment emmits a white light.

Neon Lamp
A neon lamp produces light by exciting neon gas. This gas sits in a small glass bulb. An electrode at either end of the bulb provides the current. Neon lamps must run at a fairly high voltage of around 45V and up to achieve illumination. Neon lamps are usually used as indicators in equipment, or because they have a specific voltage at which they will conduct, as triggers in strobe circuits. Neon lamps will form a dead short once that gas has begun to glow, so a current limiting resistor must be placed on one of the leads to prevent too high a current flow.

Xenon Flashlamp
Xenon flash lamps provide brilliant flashes of bright white light when triggered. A high voltage (around 350V for small lamps) is applied to the electrodes at each end. To trigger the lamp, a much higher trigger voltage is applied. This voltage is usually around 4,000V. An interesting thing about the trigger voltage is that the electrode that applies the voltgage is actually outside the glass tube in which the gas is kept, therefore it has no electrical connection. Once triggered, the gas breaks down allowing a large current to flow between electrodes. This excites the gas producing a very bright flash. Once the surge of current has stopped, the lamp is ready to be fired again. These lamps are usually used in strobes, camera flashes and on movies for effects.

Motor
A motor is a device that takes a current and converts it into a rotating motion of a shaft. The most common DC motors use a coil between two magnets. Brushes and split metal contacts are used to switch on and off the current. This AC current causes the magnets to alternately attract and repel parts of the coil, which causes it to rotate. The coil is connected to a shaft and therefore the shaft rotates with the coil.

AC Current Source
This symbol is used to represent an AC, or alternating current source. Alternating current does exactly what it's name says. The current alternates between a positive and negative voltage. AC is what comes from the standard household outlet. Note that the AC source in a schematic can come from an outlet, signal generator, oscillator, etc. The source of the current is usually mentioned in the schematic, notes, parts list or somewhere else. Whereever the source is mentioned, it is always defined as to what exactly it is.

Meter
A meter measures electricity. It does this by using a coil to pivot a needle. The coil is mounted to one end of the needle and sits between the poles of a U shaped magnet. When a current is applied, the coil will rotate. This rotation causes the neetle to pivot. The amount of coil rotation depends on the amount of current flowing through it. The symbol for meters may take on many forms, but the type of the meter is always specified in the parts list or on the schematic. Common types of meters are voltmeters (measures voltage), ammeters (measures current) and wattmeters (measures power).

Solenoid
A solenoid is a sucking magnet. Applying current causes a hollow coil of wire to suck in a iron rod. This rod can be connected to anything that must be pulled. Solenoids are used in cars, tape players, VCRs, hard drives and almost any electromechanical device.

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