Indicators and Transducers

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.

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).

Loudspeakers

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

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.

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.

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.

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.

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).

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).

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.