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Indicators and Transducers

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>>frame round<< Light Emitting Diodes

Light emitting diodes (LED's) are used as indicators in a wide variety of circuits and are available in a variety of colours, including red, green and yellow. A typical LED requires a current of between 10mA and 20mA and has a forward voltage drop of about 2.3V.

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>>frame round<< DIL Bar-graph Display

This dual-in-line bargraph display is designed for use as a signal or battery level indicator. Each of the ten segments comprises an individual light emitting diode (LED).

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>>frame round<< Loudspeakers

These two miniature moving coil loudspeakers have an impedance of 8&#937; and they are rated at 0.1&#937;. The loudspeaker provides a frequency response which extends from about 200 Hz to 10 kHz - larger units provide extended low-frequency response.

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>>frame round<< Ultrasonic Transducer

This ultrasonic transducer employs a piezoelectric element which operates at a frequency of 40 kHz. Such units are used for simple remote control applications and they are normally supplied in matched pairs - one for use as a transmitter and the other for use as a receiver.

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>>frame round<< Piezoelectric Transducer

This piezoelectric transducer is designed for use as an audible warning indicator and it provides an output at a frequency of several kHz. Such units operate with relatively high values of efficiency and the component pictured here operates over a voltage range which extends from 3V to 16V.

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>>frame round<< Light Dependent Resistor

Light dependent resistors (LDRs) exhibit a resistance which falls markedly as the incident light intensity increases. This particular LDR (an ORP12) is often used as the sensor in simple light detectors and light operated switches.

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>>frame round<< Thermistor

Thermistors exhibit a resistance which changes significantly with changes in the surrounding temperature. This particular thermistor (an RA53) is often used to stabilize the output of an oscillator by incorporating the device into a negative feedback loop.

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>>frame round<< Infra-red Detector

This infra-red detector comprises a photo-sensitive diode which has a marked peak in its spectral response at or near the infra-red region. The device is often used (in conjunction with a matched infra-red transmitter) to sense the presence (or absence) of an object (e.g. the presence of a floppy disk in a disk drive).

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>>frame round<< Infra-red Transmitter

This infra-red transmitter emits a narrow beam of infrared light. The device is normally used (in conjunction with an infrared detector) to sense the presence (or absence) of an object (e.g. the presence of a floppy disk in a disk drive).

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>>frame round<< Photo Transistor

Photo-transistors offer improved sensitivity when compared with simple diode infra-red detectors. As with their silicon photo-diode counterparts, photo-transistors have a spectral response that peaks in the infra-red region.

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