Circuit Diagram

TELEPHONE_AUDIO_INTERFACE

Published:2009/6/24 3:39:00 Author:May

The telephone audio interface-essentially, a simple isolation/couple circuit-isolates the phone line from any connected audio circuit without presenting any danger to the phone line, the equip-rnent, or the user.   (View)

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ONE_SHOT_MULTIVIBRATOR

Published:2009/6/24 3:49:00 Author:Jessie

An LM139 section can be used as a one shot   (View)

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BISTABLE_MULTIVIBRATOR

Published:2009/6/24 3:38:00 Author:May

Positive feedback is provided by resistor R4, which causes the latching. A positive pulse at the set input causes the output to go high and a reset positive pulse will return the output to es-sentially 0 Vdc.   (View)

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ac／dc_VACUUM_TUBE_AM_AND_SHORTWAVE_RECEIVER

Published:2009/6/24 3:38:00 Author:May

This circuit was used in a World War II vintage AM／SW（6 to 18 MHz）recelver and shows typical circuits used in recelvers at that time.   (View)

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BELL_SYSTEM_202_DATA_ENCODER

Published:2009/6/24 3:38:00 Author:May

The AD537 is well-suited for frequency-shift modulator and demodulator applications. Requir-ing little power, it is especially appropriate for using phone-line power. The Bell-System 202 data en-coder shown here delivers the mark frequency of 1.2 kHz with the data input low. When the input goes high, the timing current increases to 165 μA and generates the space frequency of 2.2 kHz. The trim shown provides a ±10% range of frequency adjustment. The output goes to the required band-pass filter before transmission over a public telephone line. A complementary demodulator is easy to implement.   (View)

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ELECTRONIC_THERMOSTAT

Published:2009/6/24 3:48:00 Author:Jessie

Using a 1N914 diode as a temperature sensor, this straightforward circuit has hysteresis and set-point adjustments. Usable range is about -50 to +150℃.   (View)

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TELEPHONE_SCRAMBLER

Published:2009/6/24 3:36:00 Author:May

This circuit uses the usual speech inversion algorithm, implementing it with a COM9046 ASIC. This unit is designed to fit be-Lween the handset and base of a standard telephone. It is powered by a 9-V battery.   (View)

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AM_FM_RECEIVER_CIRCUIT

Published:2009/6/24 3:48:00 Author:Jessie

This circuit shows the LM1868 as a complete AM radio and FM IF section. An extemal FM front end is used for the 88- to 108-MHz band. Audio output is 0.5 W and either 9-V battery or line operated supply can be used.   (View)

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ASTABLE_MULTIVIBRATOR_WITH_STARTING_NETWORK

Published:2009/6/24 3:35:00 Author:May

This circuit will start with a slowly rising supply voltage waveform.   (View)

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TELEPHONE_CALL_RESTRICTOR

Published:2009/6/24 3:34:00 Author:May

This circuit is designed to restrict phone calls with the area codes: 900, 976, and 540. This device uses a microcontroller to compare the DTMF decoded tones with telephone numbers stored in EEP-ROM (IC3). This device requires a programmed microcontroller. Software and details of program-ming can be found in the original magazine article.   (View)

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LM382_PHONO_PREAMPLIFIER_RIAA

Published:2009/6/24 3:47:00 Author:Jessie

  (View)

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BASIC_555_ASTABLE_MULTIVIBRATOR

Published:2009/6/24 3:47:00 Author:Jessie

F=1.44(R1=2R2)C1   (View)

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TWO_POLE_FAST_TURN_ON_NAB_TAPE_PERAMPLIFIER

Published:2009/6/24 3:47:00 Author:Jessie

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CALLER_ID_CIRCUIT

Published:2009/6/24 3:33:00 Author:May

This circuit requires programming of the microcontroller. Software information is available from the reference in the original article.   (View)

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TELEPHONE_HOLD_CIRCUIT

Published:2009/6/24 3:46:00 Author:Jessie

When the hold button S1 is pressed, SCR1 fires via R1 and R2, firing SCR1, and seizing the line via the path through R3, D1, and SCR1.   (View)

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ULTRA_HIGH_GAIN_AUDIO_AMPLIFIER

Published:2009/6/24 3:33:00 Author:May

Sometimes called the JFET μt-amp, this circuit provides a very low power, high gain amplifying function. Since pt of a JFET in-creases as drain current decreases, the lower drain current is, the more gain you get. Input dynamic range is sacrificed with increasing gain, however.   (View)

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TELEPHONE_RING_SIGNAL_DETECTOR

Published:2009/6/24 3:45:00 Author:Jessie

Discrirrtinating between telephone-ring signals on a phone line can be accomplished by using dedicated ICs, such as AT&T's LB1006AB or Texas Instruments' TMS1520A. However, if the system already is using a microcontroller, those dedicated chips can be replaced with simpler hardware and a few bytes of code.Looking at the setup, the ringing voltage pulses the optoisolator's LED, which, in turn, pulses the low-asserted RD line to the microcontroller. The firmware analyzes the pulses to determine whether a valid ringing signal is present.The frequency limits of a valid signal are 20 to 80 Hz, which is modulated 2 seconds on and 4 sec-onds off (with distinctive ringing, though, this cadence can vary). Therefore, the simplest analysis is to count down at least 20 pulses of RD in 1 second.The routine could be expanded to determine what type of ring signal is present in a distinctive ring setting. Such a system could switch the phone line to various output jacks. As a result, several phone devices could use the same line without first picking up the line to determine if it's avoice, fax, or data call.   (View)

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SHORTWAVE_RECEIVER

Published:2009/6/24 3:45:00 Author:Jessie

This receiver covers 8.5 to 11.5 MHz in two bands and has a sensitivity of under 1 μV. Nn NE602 mixer feeds a 455-kHz IF amplifier (Q1 and Q2), detector D4, and audio amplifier IC2. Q4 serves as an AGC amplifier coil data is given in the table. The LO is varactor tuned.   (View)

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ASTABLE_WITH_VARIABLE_PULSE_WIDTH

Published:2009/6/24 3:44:00 Author:Jessie

This produces a positive variable width pulse and has a symmetry control. R1 and R2 control the pulse width and symmetry.   (View)

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MOTOR_DIRECTION_CONTROL

Published:2009/6/24 3:32:00 Author:May

M1 is a small hobby dc motor.   (View)

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