Telephone or extension tone ringer

This is an improved version of the audio interface commonly used to connect a computer soundcard to a transceiver's receive and transmit audio circuits. This kind of interface is used by computer programs that send and receive SSTV, RTTY,...

Two hybrids (T1 and T2) are utilized to facilitate a direct connection to a telephone line. This circuit employs a standard speech-inversion algorithm, which inverts the frequency of an audio signal around a central frequency. An LM1496 balanced modulator...

An external horn-type speaker is optimal for this circuit. However, such devices demand significant power, so this sounder should only be employed in alarm circuits utilizing at least a 6-A SCR as the sounder driver. The circuit incorporates a...

Using an old moving coil instrument, it is quite easy to create a simple voltmeter that visually indicates the status of a telephone. A simple voltmeter can be constructed using an old moving coil instrument, which is a type of...

This circuit generates a ringing sound akin to that produced by modern telephones. It comprises three nearly identical oscillators arranged in a sequence, each responsible for generating a square wave signal. The frequency of each oscillator is determined by...

The circuit illustrated in Figure 1-560 represents a treble control potentiometer. Due to the larger capacitance values of C3 and C4 compared to C1 and C2, high-frequency signals can treat C4 as a short circuit. Consequently, the treble adjustment...