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This circuit is similar to the LED clock using 12 neon indicator lamps instead of LEDs. It operates from 2 high capacity ni-cad cells (2.5 volts) which keep it going for a couple weeks. High voltage (70 volts) for the neon lamps is obtained from a small switching power supply using a 74HC14 Schmitt trigger squarewave oscillator, high voltage switching transistor, and 10 mH high Q inductor.... [read more]

IR Remote Control Tester... [read more]

This circuit runs a fast battery test without the need of power supply or expensive moving-coil voltmeters. It has two ranges: when SW1 is set as shown in the circuit diagram, the device can test 3V to 15V batteries. When SW1 is switched to the other position, only 1.5V cells can be tested.... [read more]

This oscillator circuit permits crystals to be electronically switched by logic commands. The circuit is best understood by initially ignoring all crystals. Furthermore, assume that all diodes are shorts and their associated 1kO resistors open. The two 1kO resistors at the non-inverting input of IC1 (LT1016) set the output to half the supply, ie, +2.5V. The RC network from the output to pin 3 sets up phase-shifted feedback and the circuit looks like a wide-band unity gain follower at DC. When crystal X1 is inserted (remember, D1 is temporarily shorted) positive feedback occurs and oscillation commences at the crystal’s resonant frequency.... [read more]

A simple circuit, High-Pass filter, variable between frequencies 20HZ until 200HZ, useful in a lot of cases elaboration of sound signals. The regulation is achieved with the double potesometer 47KΩ and the frequency response in his two extreme places, appears in the schematic.... [read more]

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]