Welcome!

This circuit is intended to be placed in the same box containing the loudspeaker, forming a compact microphone amplifier primarily intended for speech reinforcement. A device of this kind is particularly suited to teachers, lecturers, tourists' guides, hostesses and anyone speaking in crowded, noisy environment. The circuit's heart is formed by the TDA7052 Audio power amplifier IC, delivering a maximum output of 1.2W @ 6V supply.... [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]

Here's a circuit that takes advantage of the photo-voltaic voltage of an ordinary LED. The LED voltage is buffered by a junction FET transistor and then applied to the inverting input of an op-amp with a gain of about 20. This produces a change of about 5 volts at the output from darkness to bright light. The 100K potentiometer can be set so that the output is around 7 volts in darkness and falls to about 2 volts in bright light.... [read more]

We've called it the Itsy Bitsy USB Lamp. It is such a delightfully simple idea we're wondering why no-one ever thought of it before. It started life (and continues) as a student project at Massey University in Wellington, New Zealand - and in fact was submitted to us by the lecturer, Stan Swan. When we say simple, we mean it: just a USB plug on a suitable length of cable, a super bright white LED and a series resistor to limit LED current. The LED and resistor are housed in an in-line fuse holder (without its innards!) which makes a superb little "wand" and also protects the electronics, such as they are.... [read more]

Producing low-distortion sine waves, this oscillator operates over the range 16 to 22000 Hz.... [read more]

Is the battery empty, or is there something wrong with the device? That’s always a difficult question when your walkman or some other battery-powered device appears to be dead when you switch it on. Before you take it to the shop for servicing, the first thing you should do is to test the battery or batteries. Of course, this means you need a reliable battery tester, but it also means you can limit the damage to the cost of a battery or two and a one-time investment of time and money in building a suitable tester.... [read more]