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Using this circuit, audio musical notes can be generated and heard up to a distance of 10 metres. The circuit can be divided into two parts: IR music transmitter and receiver. The IR music transmitter works off a 9V battery, while the IR music receiver works off regulated 9V to 12V. First diagram shows the circuit of the IR music transmitter. It uses popular melody generator IC UM66 (IC1) that can continuously generate musical tones.... [read more]

A opamp. medium power, here it‘s used as amplifier of headphones with possibility drive low loads. It contains in a nutshell two amplifiers.... [read more]

This circuit shows how to use an ordinary LED as a light sensor. It makes use of the photovoltaic voltage developed across the LED when it is exposed to light. LEDs are cheaper than photodiodes and come with a built-in filter, which is useful when the application involves colour discrimination. The photo-voltage of a red LED (its bandgap voltage) is typically about 2V. The source impedance of this voltage is about 800MΩ in daylight, rising to infinity in darkness. A TL071 JFET input op amp is used to amplify and buffer this extremely high impedance signal.... [read more]

The circuit will give us 10 amps (12 amps surge) with performance that equals or exceeds any commercial unit. The circuit even has a current limiting feature which is a more reliable system than most commercial units have.... [read more]

This circuit is intended to signal, through a flashing LED, the exceeding of a fixed threshold in room noise, chosen from three fixed levels, namely 50, 70 & 85 dB. Two Op-amps provide the necessary circuit gain for sounds picked-up by a miniature electret microphone to drive a LED. With SW1 in the first position the circuit is off. Second, third and fourth positions power the circuit and set the input sensitivity threshold to 85, 70 & 50 dB respectively. Current drawing is 1mA with LED off and 12-15mA when the LED is steady on.... [read more]

This low-cost short-wave transmitter is tunable from 10 to 15 MHz with the help of ½J gang condenser VC1, which determines the carrier frequency of the transmitter in conjunction with inductor L1. The frequency trimming can be done with VC2. The carrier is amplified by transistor T4 and coupled to RF amplifier transistor T1 (BD677) through transformer X1*. The transmitter does not use any modulator transformer.... [read more]