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Here they exist two regulator circuits, that use the IC L200, as regulator of voltage and current, the company SGS-Thomson, which give these circuits. In circuit Fig.1, we can regulate the output voltage, with the RV1, while in the Fig.2, we can regulate also output voltage – current, with the TR2 and TR1, respectively. More information on characteristics for L200, you can see in list datasheets. Shortly will be added also certain other useful circuits with L200.... [read more]

Three 2nd order filters are shown, low pass, high pass, and bandpass. Each of these filters will attenuate frequencies outside their passband at a rate of 12dB per octave or 1/4 the voltage amplitude for each octave of frequency increase or decrease outside the passband.... [read more]

This circuit, enclosed in a small plastic box, can be placed into a bag or handbag. A small magnet is placed close to the reed switch and connected to the hand or the clothes of the person carrying the bag by means of a tiny cord. If the bag is snatched abruptly, the magnet looses its contact with the reed switch, SW1 opens, the circuit starts oscillating and the loudspeaker emits a loud alarm sound. A complementary transistor-pair is wired as a high efficiency oscillator, directly driving a small loudspeaker. Low part-count and 3V battery supply allow a very compact construction.... [read more]

The bi-directional sequencer uses a 4 bit binary up/down counter (CD4516) and two "1 of 8 line decoders" (74HC138 or 74HCT138) to generate the popular "Night Rider" display. A Schmitt Trigger oscillator provides the clock signal for the counter and the rate can be adjusted with the 500K pot.... [read more]

Here's a top-class headphone amplifier that can drive high or low impedance 'phones to full power levels, with very low noise and distortion. For best performance, it can be teamed with the Stereo Preamplifier described last month. Alternatively, it can be used as a standalone unit, requiring only a power supply and a volume control pot for use with any line-level signal source (CD/MP3 player etc). It even includes dual outputs, so you can listen with a friend!... [read more]

This circuit takes an ordinary loudspeaker and allows it to be used in reverse, as a microphone.... [read more]