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Telephone / Mobile Circuits

2 Line Intercom Cum Telephone Line Changeover Circuit

2 Line Intercom With Telephone Line Changeover Circuit: The circuit presented here can be used for connecting two telephones in parallel and also as a2-line intercom.

56K RF Modem

8 Line Intercommunication using 89c51

9 Line Telephone Sharer: This circuit is able to handle nine independent telephones (using a single Telephone line pair) located at nine different locations, say, up to a distance of100m from each other, for receiving and making outgoing calls, while maintaining conversation secrecy. This circuit is useful when a single Telephone line is to be shared by more members residing in different rooms/apartments.

900Mhz 9600bps Link

9-Line Telephone Sharer

Caller ID:

Caller ID / DTMF Audio Decoder:

Caller ID Circuits: information and circuits for different systems used USA and Finland

Caller ID Decoder:

Caller ID Decoder Part 1:

Caller ID Decoder Part 2:

Caller ID Display Service: Caller ID decoder based on 68HC11, text in French

Cell-Phone-Controlled Audio/Video Mute Switch:

Chip recorder customizes phone ringer: 07/25/2002  EDN - Design Ideas / Companies usually purchase one type of telephone for all employees, which is understandable, especially if they obtain a discount for buying in quantity. One ringer sound for everyone can pose a problem, though, if the sound of a ringing phone makes a dozen people pause and look at their telephones. Equally annoying is the absence of a visual message indicator.

Circuit Detects When A Shared Telephone Line Is In Use: 01/08/01 Electronic Design - Ideas for Design / The circuit shown can detect when a shared telephone line is in use (see the figure). This is particularly useful when an automated device wishes to place an outgoing call without disturbing an. . .

Circuit Provides Ground-Start Supervision For Phone Switching: 11/20/00 Electronic Design - Ideas for Design / Ground start is the primary analog signaling method used between telephone switches such as the central office (CO) and a private branch exchange (PBX). It offers a way to indicate on-hook and off-hook conditions in a voice network. There’s one. . .

Circuit Provides Message on Disabled Phone Line: 01/20/00 EDN-Design Ideas / PDF contains multiple circuits - scroll to find the one of interest / This circuits plays a prerecorded message into any phone on the line when its receiver goes off-hook

Circuit Translates a Law to µ Law: 05/07/98 EDN-Design Ideas / Two common methods exist to command voice for transmission through a PCM channel

Circuit Vocalizes Telephone Number: 02/03/94 EDN-Design Ideas

Clip extracts signal from phone line: 07/24/03  EDN-Design Ideas / Using a capacitive-coupled clip, you can pick up the signal from a twisted-pair or wire telephone line or from other unshielded analog lines without piercing the insulation. No line test can detect the clip's presence, and it leaves no evidence of having been attached. It needs no ground return. You can fasten the small, insulated pickup plates to the opposing jaws of an alligator clip …

Contact less Ringer for Telephones:

Cordless Phone Backup:

Creating your Own Telephone Ne2 Rk: you can easily create your own intercom system using two telephones, a 9-volt battery (or some other simple power supply) and a300-ohm resistor

Cut Phone Line Detector:

Cut Phone Line Detector #1: Can be used to alarm security system

Cut Phone Line Detector #2:

DC / DC Converter operates From Phone Line: 01/15/98 EDN-Design Ideas

Detect Loop-Reverse Battery Conditions On A Telephone Line: 02/18/02 Electronic Design - Ideas for Design / Equipment connected to the public switched-telephone network (PSTN) sometimes needs to detect polarity reversals of the battery feed. One common application is the Direct-Inward-Dialing (DID) service that uses what is termed as "loop-reverse battery. . .

Detecting a Telephone Ring:

Digisound Ring Modulator:

Digital / Standard Phone Line Tester: make sure that the line is suitable for modem use and your PCMCIA does not damage if you plug it in

Doorphone Intercom:

DSL Filter (phone-line):

DTMF Coder Makes Low Cost Sine Wave Generator: 10/13/94 EDN-Design Ideas  

DTMF Decoder / Logger:

DTMF Generation With 3.58 MHz Crystal: National Semiconductor Application Notes first published05-Aug-1995

DTMF Products for you: DTMF decoder can be powered from a 9V battery or from your parallel printer, schematic and windows demo program, design by Schmidt Technologies

DTMF Proximity Detector:

DTMF Receiver IC MT8870 Tester:

DTMF Tone Decoder: hears touch tones and displays them as telephone numbers.

Dual Tone Multiple Frequency DTMF: National Semiconductor Application Notes first published04-Nov-1995

Electronic Dazer:

ELF Telephone Audio Pickup:

FM Radio Telephone Bug:

FM Radio Telephone Transmitter:

FM Telephone Bug:

Free Line Indicator Stops Interruptions: 12/07/00 EDN-Design Ideas / PDF contains multiple circuits - scroll to find the one of interest A simple circuit lights an LED, which indicates whether the line is free (Figure1a) / PDF contains multiple circuits - scroll to find the one of interest. Batteries are unnecessary; the phone line powers the circuit, and an accumulator saves energy for an "in use" indication.

Generate CID / CIDCW Analog Signals: 12/07/00 EDN-Design Ideas / PDF contains multiple circuits - scroll to find the one of interest / A high-speed µP can generate CID (caller-ID) / PDF contains multiple circuits - scroll to find the one of interest and CIDCW (caller-ID-on-call- waiting) / PDF contains multiple circuits - scroll to find the one of interest analog signals at1200 baud FSK between the first and second20-Hz ring of an incoming call

Hold Function for Telephone:

Home Made PBX / PABX:

Interface Cables for Various Cell Phones:

Isolated Telephone Interface: This circuit allows you to record audio from a Telephone line into a tape recorder or computer soundcard. Most of the parts for this circuit can be scrounged from an old modem, with some work, it is possible to rewire the modem circuitry and use the old modem case.

Laser Telephone Receiver Circuit:

Line Status Indicator:

Link Telephone Intercom-DTMF Version:

Low Cost PCO Billing Meter:

Mobile Cellphone Charger:

Mobile Phone Battery Charger:

Multipurpose Circuit for Telephones: 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, and ringing modes. It can also be used to connect the telephone to a cid (caller identification device) through a relay and also to indicate tapping or misuse of telephone lines by sounding a buzzer.

Music On Hold for Telephones:

NCDS Interface Schematic for Nokia 3110, 8110, 8110i:

Noise Reduction (Filter) Circuit:

Nokia 3210 MBUS Interface:

Nokia 5190 / 6190 Data Cable:

Off Hook Phone Line Supplies 150 MW: 09/01/94 EDN-Design Ideas

Off Line Telephone Tester

Old Phones As An Intercom:

Parallel Telephone With Secrecy and Call Prevention:

Parallel Telephones With Secrecy:

Parallel Telephones With Secrecy: This system will enable the incoming ring to be heard at both the ends. The DPDT switch, installed with each of the parallel telephones, connects you to the line in one position of the switch and disconnects you in the other position of the switch. At any one Time, only one telephone is connected to the line. To receive a call at an end where the instrument is not connected to the line, you just have to flip the toggle switch at your end to receive the call, and act as usual to have a conversation. As soon as the position of the toggle switch is changed, the line gets transferred to the other telephone instrument.

Personal Silent Alarm System:

Phone "Hold" With Music:

Phone Broadcaster:

Phone Busy Indicator: simple busy indicator, does not meet regulations of many countries because this circuit draws excessive continuous current from the ph1-line even when not active and this can cause problems with Telephone system

Phone Hold With Music:

Phone in Indicator:

Phone in use:

Phone In Use indicator:

Phone In Use Light:

Phone line indicator:

Phone Line Monitor:

Phone Line to Audio:

Phone Off Hook Indicator:

Phone Rang Indicator Light:

Phone to Audio Interface:

Phone-line-voltage monitor meets FCC specs: When you design equipment that interfaces to a phone line, it is often desirable to be able to monitor the dc voltage on the line. This ability can be useful, for example, to determine whether a line is in use before attempting to go off-hook and possibly interrupting somebody's phone call. FCC regulations place strict limits on the amount of leakage current an on-hook device can draw from a phone line.

Playing a Mac through a Standard Telephone Line: how to get sound from computer to Telephone line

Precision circuit closely monitors –48V bus: 10/17/2002  EDN - Design Ideas / Ever-greater complexity in communications systems has spurred a need for power-supply management. POTS (plain-old telephone systems) obtain power from –48V supplies backed by arrays of batteries in central offices and distributed throughout copper lines. Although nominally –48V, the voltage on the lines can vary from –40 to –80V, and the voltage is subject to surges and ....

Ringing Phone Light Flasher: when the ph1-rings, lights connected to circuit flash

Ringing Phone Light Flasher:

Silent Telephone Alert:

Simple Circuit to Connect telephone Equipment to Audio Mixer:

Simple Phone Tap:

Simple Phone Tap #1: will record any conversation on any ph1-on same line, the circuit seems to be a bad design because it does not provide proper isolation and has too low DC impedance (can keep you line off-hook all the Time)

Simple Telephone Recorder: This recorder can be connected to the telephone lines just about any place, and no external power source is needed. The tape recorders switch terminals are applied to a pair of transistors, connected as Darlingtons, that are used to turn the recorder on and off. When the telephone is off-hook theres usually about50 VDC across the phone thats divided over R1, R2, and R4, so that Q1s base is negative enough to keep the recorder off. Pick up the receiver, and the voltage drops to5 V. That leaves not quite-enough voltage on Q1s base to keep that transistor at cutoff, so the recorder begins. Remember to keep your recorders switch in the on position, and depending on how many people use the telephone, remember to rewind or change tapes occasionally!

Simple Telephone Ring Tone Generator:

Smart Ringing Phone Light: The circuit shown here is used to switch on a lamp when the Telephone rings, if the ambient light is insufficient.

Soft Musical Telephone Ringer:

Soft Musical Telephone Ringer:

Soft On / Off Switch:

Substitute Phone Power Supply Stops Hum During Audio Testing: 06/09/03 Electronic Design - Ideas for Design /When developing quality devices that interface with telephone lines, sensitive audio measurements are sometimes needed. However, both frequency noise and distortion added by the test equipment—as well as low-frequency signals derived from the

Switched Capacitor IC and Reference Form Elegant –48 to +10 Volt Converter: 04/24/03 EDN-Design Ideas /PDF contains multiple circuits - scroll to find this circuit

Talking Phone Dial Monitor:

Taxi Phone Automatic Dialler:

Telephone amplifier:

Telephone Audio Interface:

Telephone Autodialler:

Telephone Call Meter Using Calculator And COB:

Telephone Controlled Night Light: When the telephone rings, or when the handset is lifted, the night light is turned on and remains on while the conversation takes place. When the handset is replaced in the cradle, the light remains on for about11 s. During standby conditions, the -28Vdc bias on the phone line maintains the output of U3 in a high state. When the ac ring signal is applied to the phone line, it is processed by the ring detector U1, producing a negative output pulse at pin2 for each ring. These pulses trigger U2, causing its output to become high and the discharge transistor to turn off.

Telephone Conversation Recorder:

Telephone Conversation Recorder #1: This circuit enables automatic switching-on of the tape recorder when the handset is lifted. The tape recorder gets switched off when the handset is replaced. The signals are suitably attenuated to a level at which they can be recorded using the ‘MIC-IN’ socket of the tape recorder

Telephone Conversation Recorder #2: This circuit enables automatic switching-on of the tape recorder when the handset is lifted. The tape recorder gets switched off when the handset is replaced. The signals are suitably attenuated to a level at which they can be recorded using the ‘MIC-IN’ socket of the tape recorder

Telephone Headgear: A compact, inexpensive and low component count telecom head- set can be constructed using two readily available transistors and a few other electronic components. Since the circuit draws very little current, it is ideal for parallel operation with electronic Telephone set. FAIR WARNING -- THIS SITE HAS ANNOYING POP UP ADS.

Telephone Hold Button:

Telephone Hold Button #!:

Telephone In Use LED Indicator:

Telephone in use Light:

Telephone In Use Relay Circuit:

Telephone Interface Circuits:

Telephone Line Audio Interface Circuits: Telephone recording, Telephone line to mixer and Telephone hybrid circuits

Telephone Line Based Audio Muting & Light on Circuit

Telephone Line Based Audio Muting & Light On Circuit #1: The circuit would automatically light a bulb on arrival of a telephone ring and simultaneously mute the music system/TV audio for the duration the telephone handset is off-hook. Lighting of the bulb would not only indicate an incoming call but also help in locating the telephone during darkness.

Telephone Line Based Audio Muting & Light On Circuit #2: The circuit would automatically light a bulb on arrival of a telephone ring and simultaneously mute the music system/TV audio for the duration the telephone handset is off-hook. Lighting of the bulb would not only indicate an incoming call but also help in locating the telephone during darkness.

Telephone Line Based Audio Muting And Light-On Circuit:

Telephone Line Monitor #2:

Telephone line monitor 1:

Telephone line monitor 2:

Telephone Line Simulator #1:

Telephone Music on hold Box:

Telephone Number Display:

Telephone Number Display #1:

Telephone Number Display #2: The given circuit, when connected in parallel to a telephone, displays the number dialed from the Telephone set using the DTMF mode. FAIR WARNING -- THIS SITE HAS ANNOYING POP UP ADS.

Telephone operating Parameters:

Telephone Power?:

Telephone Privacy Adapter:

Telephone Privacy Adapter:

Telephone Receiver:

Telephone Record Control: allows you to connect any tape recorder that has a mic and remote input to a ph1-line and automatically record both sides of a conversation when ever the ph1-is in use

Telephone Recorder #1: This circuit lets you record your ph1-conversations automatically, notice that this circuit does not provide isolation between Telephone line and the recorder

Telephone Recorder #2: This circuit automatically records all incoming and outgoing phone-conversations with an ordinary cassette or tape recorder. The circuit below distills the audio signal from the phone-line and automatically starts/stops the cassette recorder.

Telephone Recording Circuit #1:

Telephone Recording Circuit #2: How they work and some example 

Telephone Related ASCII Schematics: wide collection of Telephone circuits

Telephone Ring Controlled Relay:

Telephone Ring Detector:  This is a great project to build with a complete run down of the circuit operation included all parts are listed.

Telephone Ring Detector #1: This circuit uses a4N35 to form a Telephone ring detector. The ringing voltage pulses the optoisolators LED, which in turn pulses the low-asserted "not" 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 are20 to 80 Hz, which is modulated2 seconds on and4 seconds off (with distinctive ringing, though, this cadence can vary). Therefore the simplest analysis is to count down at least20 pulses of "not" RD in1 second. Source: "Electronics Design" Magazine, Aug,22, 94

Telephone Ring Generator  :

Telephone Ring Generator Using 60Hz Power Transformer:

Telephone Ring Generator Using Switching Power Supply:

Telephone Ringer : The circuit requires four Astable multivibrators for its working. Therefore two556 ICs are used here. The IC556 contains two Timers (similar to555 ICs) in a single package. One can also assemble this circuit using four separate555 ICs. The first multivibrator produces a rectangular waveform with1-second ‘low’ duration and2-second ‘high’ duration. This waveform is used to control the next multivibrator that produces another rectangular waveform.

Telephone Ringer Circuit: Low cost, easy to build Telephone ringer circuit.

Telephone Ringer using Timer ICs:

Telephone Ringer Using Timer ICs:

Telephone Ringing Circuits: how to detect ringing and how to make phones ring

Telephone Tap: Amplify or record a telephone call with the simple circuit shown. The 8-W secondary winding of a miniature transistor output transformer is connected in series with either of the telephone lines. The1000-W primary winding can feed either a cassette recorder or an audio amplifier.

Telephone Test Circuit With Audio Mixer: get Telephone audio to mixer or send audio to Telephone

Telephone Transmitter #1:

Telephone Transmitter #2:

TeleRemote Control:

Tele-Scope:

The Link 4+0 – Internal Intercom:

The Original 2 Phone Link Design:

Three-Wire Cables Connect Low-Cost, Low-Power Interphone: 01/24/00 Electronic Design - Ideas for Design / The "point-to-multipoint" interphone system shown in Figure 1 and Figure 2 utilizes separate three-wire cables to connect one local station to a maximum of six. . .

Two Line Intercom Cum Telephone Line Changeover Circuit:

Two Line Intercom With Telephone Line Changeover Circuit: The circuit presented here can be used for connecting two telephones in parallel and also as a2-line intercom.

Universal Telephone Hold:

Use old Phones As An Intercom:

Using the Comrex Hotline or Vector on a Dry Pair: how to use simple pair of wires with no voltage, ringing signals to interconnect normal Telephone line devices

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