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Infa-Red Remote Control

his remote transmits a tone using an infa-red LED. This tone is decoded by the receiver. Since the receiver only switches when it "hears" the tone, there are no accidental activations.... [read more]

Symmetrical from a single voltage supply

Many times we needed symmetric voltage, but we do not have the possibility him of taking immediately, from a existing supply. Then it will be supposed him we create from the existing single.... [read more]

Fridge Door Alarm Schematic 2nd Version

The circuit, enclosed in a small box, should be placed in the fridge near the lamp (if any) or close to the opening. With the door closed, the interior of the fridge is in dark, the photo resistor R2 presents a high resistance (>200K) thus clamping IC1 by holding C1 fully charged across R1 and D1. When a beam of light enters from the opening, or the fridge lamp lights, the photo resistor lowers its resistance (<2K) stopping C1 charging current.... [read more]

Simple Adjustable Voltage Source

A simple but less efficient methode of controlling a DC voltage is to use a voltage divider and transistor emitter follower configuration.... [read more]

FET Audio Mixer

This simple circuit mixes two or more channels into one channel (eg. stereo into mono). The circuit can mix as many or as few channels as you like and consumes very little power.... [read more]

Automatic Loudness Control

In order to obtain a good audio reproduction at different listening levels, a different tone-controls setting should be necessary to suit the well known behaviour of the human ear. In fact, the human ear sensitivity varies in a non-linear manner through the entire audible frequency band, as shown by Fletcher-Munson curves. A simple approach to this problem can be done inserting a circuit in the preamplifier stage, capable of varying automatically the frequency response of the entire audio chain in respect to the position of the control knob, in order to keep ideal listening conditions under different listening levels.... [read more]