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It is a very useful thing , to have a small headphone amplifier , capable of driving a couple of pairs phones. Fortunately, the headphone amp has a much easier job to do, in that neither the output power requirements nor the load characteristics are so severe, since headphones typically have a load, impedance , higher of 50 ohm, (typical 600 ohm), and only require 1-2V RMS. max, for normal output.... [read more]

This frequency doubler using a single 4069 hex inverter IC, a frequency doubler can be constructed to give an output pulse train whose frequency is twice that of a squarewave input signal.... [read more]

This device was designed on request; to control the light intensity of four filament lamps (i.e. a ring illuminator) powered by two AA or AAA batteries, for close-up pictures with a digital camera. Obviously it can be used in other ways, at anyone's will.IC1 generates a 150Hz square wave having a variable duty-cycle. When the cursor of P1 is fully rotated towards D1, the output positive pulses appearing at pin 3 of IC1 are very narrow.... [read more]

This circuit is a small digital “roulette''. It is constituted by oscillator IC1, the counter IC2, the transistors Q1-7 that drive the display common cathode DSP1. The supply basically becomes from a battery 9V, but can become also from one power supply.... [read more]

The circuit illustrates generating a single positive pulse which is delayed relative to the trigger input time.... [read more]

Here the popular 555 timing IC, is wired as a monostable. The timing period is precise and equivalent to: 1.1 x R1 x C1... [read more]