An audio source, like a mixer, preamp, EQ, or a recorder, is fed to the input of the Electronic Crossover Circuit. This signal is either AC or coupling, depending on the setting of switch 51, the non-inverting input of buffer amplifier Ul-a, a section of a quad BIFET, low amp TL074 noise made by Texas Instruments op. This stage has a gain of 2, and its output is distributed to both a low pass filter made by R4, R5, C2, C3, and Uld op-amp, and a high-pass filter made by R6,.....
This decoder will respond to a preselected 4-digit DTMF number. IC7 is a Radio Shack IC device (part #276-1303..
The XR-T5990 single-chip pulse/tone Dialer is a silicon gate CMOS circuit which performs both pulse and tone functions. It is designed to operate directly from the telephone line or on a separate small power supply. ..
The telephone-line tester consists of nothing more than a meter (that`s used to measure line voltage in the on- and off-hook state), three resistors (one of which is variable), a pushbutton switch, and a modular telephone connector...
A neon lamp can easily be added to the phone line to act as a ring indicator...
With the 555 timer connected as a multivibrator and an opto-isolator, ..
This is a complete telephone bell replacement circuit with minimum external components with on-chip diode bridge and transient protection..
The circuit has been designed to accommodate all those who dedicate many hours of their lives by exploring the endless pages of this site. Despite the fact that it consists of only three components (Most were not little!), Is able to provide an indication of whether it actually released the telephone line after a long connection via modem to the network. This can be particularly useful, since there In many cases, the computer claims that the telephone network connection.....
This circuit uses ML8204/ML8205 devices..
IC-1 and the associated circuitry form a stable audio tone generator that feeds a buffer amplifier, Ql and Q2. The tone output is taken from the emitters of the transistor pair to supply a carrier voltage for a balanced modulator made up of four diodes—Dl through D4—and Tl and T2. If the two transformers and the four diodes are perfectly matched (which is almost impossible to achieve and not necessary in any case) no carrier will appear at the input or output.....
This circuit consists of two audio channels, a control circuit, and a hybrid irlterface circuit. The gain of each audio channel is con· trolled by the control circuitry, with the use of a voltage controlled amplifier (VCA). The inputs to the control circuit are obtained from each of the audio channels. The hybrid interface circuit performs three important functions. First, it couples the Tx channel signal to the telephone line. ..
This circuit functions as a line-current sensor and can be connected in series with either of the phone lines. For the circuit to indicate an "in use" status for all phones on a single line, it must be connected in series with the phone line before, or ahead of all phones on the line...
Audio from the telephone is inductively coupled to the base of Ql. which is used as a preamp. The preamp provides a gain of about 75 dB, to boost the input signal from .about 4 mV to about 300 mV pk-pk. If you use a higher gain transistor, increase the value of R9 to produce a Q point, measured from minus to the collector of Ql, of one-half the supply voltage. ..
The XR-T5995 Speech Network is a monolithic integrated circuit specifically designed for implementing a low cost telephone circuit. ..
This circuit converts a tape recorder into a completely automatic telephone conversation recording instrument that needs no external power source. Voltage at the switch terminals of tape recorder applied to a pair of Darlington-connected transistors, Ql and Q2, will turn on and start the tape recorder. To turn the transistors off, and thereby stop the machine, apply a negative voltage to the base of Ql from the phone line..
The ultra-simple one-transistor, IR transmitter shown is designed to transmit the sound from any 8 or 16 ohm audio source, such as a TV, radio, or tape recorder on an infrared beam of light. ..
This circuit is useful for signal-processing sonar data recorded on an instrumentation-quality analog tape recorder. The envelope detector utilizes ready available parts, and furnishes accuracy beyond 100 kHz. Two LM301 op amps connected as precision absolute-value circuits use 2-pole frequency compensation for increased slew rate. ..
The cireiilt is built around a couple of low-cost ICs: an H11C4 optoisolator/coupler with an SCR output (Ul) and an LM3909 LED flasher (U2). It is connected to the phone line in the same manner as any extension phone. A ring signal on the telephone activates the opt,oisolator/SCR. and causes U2 to flash LED1...
The LED flickers when the phone is ringing or being dialed..
The design consists of an amplifier, a double-pole changeover switch and two loudspeakers: one for the master station and..
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