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Outband descrambler – Circuit Schematic
Outband descrambler
For the outband decoder shown here to work, the cable company must provide at least a 1 millivolt signal. Values for C1-C5 and L1-L4 ore found In Table 1. This ...
Modem shutdown Indicator – Circuit Schematic
Modem shutdown Indicator
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...
Phone Busy Indicator schematic – Circuit Schematic
Phone Busy Indicator schematic
This indicator shows whether the phone is busy or not. When the line is busy, LED D6 off. The line voltage at points A and B attached. By the rectifier bridge b...
Phone line busy indicator – Circuit Schematic
Phone line busy indicator
This is the most simple phone busy indicator is possible with only three parts. Connect the circuit so that the green light illuminates when the line is free. I...
Phone line in use drives Relay – Circuit Schematic
Phone line in use drives Relay
Circ?it to close a relay when any phone extension is off-hook. Uoltage at the gate of the MOSFET sho?ld be negative (1-3 volts) with respect to the so?rce then ...
Audio interface for Telephone line – Circuit Schematic
Audio interface for Telephone line
Audio from a telephone line can be obtained using a transformer and capacitor to isolate the line from external equipment. A non-polarized capacitor is placed i...
Ring Generator Using a Transformer – Circuit Schematic
Ring Generator Using a Transformer
This ring generator will ring a telephone once every 10 seconds. The interval between rings can be lengthened or shortened by varying the value of the 1 Meg res...
Telephone Line Simulator Schematic – Circuit Schematic
Telephone Line Simulator Schematic
The following text describes construction, testing and use of an electronic telephone line simulator of my own design. This self-build project can simulate a te...
Antenna ground loop Isolator – Circuit Schematic
Antenna ground loop Isolator
A ground loop in your AV system caused by antenna connection or TV cable is very common if you have your computer connected to the same system. This type of gro...
Phone line FM transmitter – Circuit Schematic
Phone line FM transmitter
Here is a simple yet very useful circuit which can be used to eavesdrop on a telephone conversation. The circuit can also be used as a wireless telephone amplif...
Telephone call meter circuit – Circuit Schematic
Telephone call meter circuit
In this circuit, a simple calculator, in conjunction with a COB (chip-on-board) from an analogue quartz clock, is used to make a telephone call meter. The calcu...
Privacy in parallel telephone line – Circuit Schematic
Privacy in parallel telephone line
Often a need arises for connection of two telephone instruments in parallel to one line. But it creates quite a few problems in their proper performance, such a...
Off-line Telephone indicator – Circuit Schematic
Off-line Telephone indicator
H ere is a circuit of an off-line telephone tester which does not require any telephone line for testing a telephone instrument. The circuit is so simple that ...
Phone line Audio Visual Ringer – Circuit Schematic
Phone line Audio Visual Ringer
Many a times one needs an ex- tra telephone ringer in an ad- joining room to know if there is an incoming call. For example, if the telephone is installed in th...
Telephone Headphone amplifier – Circuit Schematic
Telephone Headphone amplifier
A compact, inexpensive and low component count telecom head- set can be constructed using two readily available transistors and a few other electronic component...
Telephone DTMF decoder Display – Circuit Schematic
Telephone DTMF decoder Display
The given circuit, when connected in parallel to a telephone, dis- plays the number dialled from the telephone set using the DTMF mode. This circuit can also sh...
Telephone Ringer using 556 – Circuit Schematic
Telephone Ringer using 556
Using modulated rectangular waves of different time periods, The circuit presented here produces ringing tones similar to those produced by a telephone. The ci...
Audio and Visual Telephone ringer – Circuit Schematic
Audio and Visual Telephone ringer
Many a times one needs an extra telephone ringer in an ad joining room to know if there is an incoming call. For example, if the telephone is installed in the d...
Telephone line interfacing – Circuit Schematic
Telephone line interfacing
This add-on device for telephones can be connected in parallel to the telephone instrument. The circuit provides audio-visual indication of on-hook, off-hook,...
Advanced Phone in use circuit – Circuit Schematic
Advanced Phone in use circuit
This project has two features. It will let you know when a single phone is using the line and also when two phones are on the line! The green LED indicates the...