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Telephone Circuits

Telephone Circuits:   #'s - B       C - F       G - K       L - Q       R - S      T - Z

Last Updated: October 24, 2017 02:55 PM

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Parallel Telephone with Secrecy -  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 as over loading and...__ Electronics Projects for You

Parallel Telephone with Secrecy & Call Prevention -  This circuit provides secrecy when two or more telephones are connected in parallel to a telephone line.  The circuit also prevents incoming calls to as well as outgoing calls from other...__ Electronics Projects for You

PCO billing meter -  The circuit presented here can be used in PCOs for displaying the actual bill.  The comparative disadvantages of the presented circuit are as follows: 1.  The calculator used along with this circuit...__ Electronics Projects for You

PCS Phone Jammer -  Schematic only __ Designed by va3iul

PCS: Not Just Another Cell Phone -  11/21/96 EDN-Design Feature  Low-cost, high-functionality digital chip sets are becoming available for wireless base-station and terminal, or handset, applications, making personal communications service (PCS] affordable enough for mass-market deployment.  As new capabilities emerge, PCS may even begin to rival wireline telephones as the predominant way __ Circuit Design by Stephen Kempainen, Technical EDFtor

Phone Amplifier -  it's a useful 0.5 watt amplifier for phone line, powered by a simple 10 volt supply, it uses an isolated trasformer to get the sound from the telephone line and an audio  transformer for the amplifier __ Designed by Alfred73

Phone Bell Auto Silencer -  Telephone ringing all of a sudden in the middle of a serious meeting is quite irritating.  The automatic bell silencer circuit described here is the answer to this problem.  By pressing...__ Electronics Projects for You

Phone Broadcaster -  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 amplifier.  One important feature...__ Electronics Projects for You

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.   __ Designed by Aaron Cake

Phone FM Transmitter -  This Phone FM transmitter connects in series to your telephone line and transmits the telephone conversation over the FM band when you pick up the telephone handset.  Transmitted signal can be tuned by any FM receiver.  The circuit includes an "On Air" LED indicator and also provides a switch which can be used to turn off the transmitter.  A unique feature of the circuit is that no battery is needed to operate the circuit since power is taken from the telephone line.  __ 

Phone Hold with Music -  This circuit will allow you to place a phone call on hold and if you wish to have them listen to music while they are on hold.  The circuit operates as follows: The RED wire from the phone jack.   __ Contact IQ Technologies 

Phone in use indicator 1 -  Use a CMOS 4049 Hex interter because (supposedly) has high drive output.  And since it's CMOS , it can operate with Vcc from +3 to +15V.  And it has a high input impedence.   __ Designed by Roger Petersen

Phone in use indicator 2 -  LED will start blinking if a phone is in use__ 

Phone in use indicator 3 -  Now here's some logic that should work fine with the right zener and the right resistors and a couple of cheap NPN's 2n2222A's or 2n3904's (06's?).  if you get close to 25 volts with the new smart test boxes, a 20 volt Z may work fine.  Choose R1 to limit current through Z and have enough left to turn on NPN1 just enough to deprive NPN2, choose R2 for that, and you will need to add a resistor R3 to protect the LED from overcurrent as needed, depending on the phone system you have!
 __ Designed by Richard Steven Walz

Phone in use indicator 4 -  The circuit I built gives a visual indication at each extension when any extension is off-hook.  it is line-powered, and the maximum number that can be used on our system is three.  Since they all draw power at the same time to light the LEDs, any more indicators would cause an off-hook condition.  Some changes could be made to reduce the current draw, to allow using more indicators, but the brightness of each LED would suffer.  The LEDs I used are tiny, but.   __ Designed by Kenneth Carver

Phone in use indicator 5 -  Schematic only, no description included __ Designed by Terri Barber

Phone in use indicator 6 -  R1 and R2 form a voltage divider, insuring that the phone line sees a high impedance load and that high voltages (such as the ring voltage) are easily dissipated by the protective diodes (CR1 and CR2).  Also (obviously) they serve to divide all incoming voltages by two.  Capacitor C1 filters out some of the audio signals that might otherwise make the LED flicker with speech__ 

Phone in use indicator 7 -  LED will light up if a phone is in use.   __ Designed by Schematic only, no description included

Phone Intercepter 1 -  PIC  Project  This device connects between the phone line, an answering machine, and your phones.  When a phone call comes in, the answering machine picks up the call and informs the caller to enter the access code to ring the phone or to wait for the beep and leave a message.  if the correct code is entered, the answering machine is immediately disconnected while the device generates phone ringing tones on an external speaker.  Picking up any phone causes the device to return to its initial state.   __ Designed by Luhan Monat-Mesa Arizona

Phone Interceptor 2 -  PIC  Project  This unit is an upgrade of the previous phone call interceptor.  instead of using an answering machine to provide the outgoing message and recording functions, it uses the iSD4004 (from Windbond Electronics).  The iSD4004 records up to 8 minutes of audio.  I use the first several seconds for outgoing message prompts.  The remaining time is used to record up to 30 messages, depending on message length.   __ Designed by Luhan Monat-Mesa Arizona

Phone Light Flasher -  This is very useful in a situation were there is lots of noise and it is impossable to hear the phone, such as a workshop.  Here is such a device.  The ring detect part of this circuit came from [url]http://www.  hut.  fi/Misc/Electronics/circuits/telephone_ringer.  html[/url].  Notes: 1.  You may need to use a lower voltage zener for D1 and D2.2.  You can use a regular relay instead of a solid state relay, but the arcing accross the contacts may destroy it pretty quickly.3.  Be very sure that you have not accidentally connected 120V to the phone line when building and installing this __ Designed by Aaron Cake

Phone Line Box -  This is an educational site of PIC  Projects in various stages of development along with pictures, source files, object code files, schematics, and board layouts.  You are welcome to use what you like at your own risk.   __ Designed by Luhan Monat-Mesa Arizona

Phone Line Controller -  it might be "yet another" «device» controller that operates over phone-line, but this one works for sure :) The task was to build a device that connects to the phone line and has a relay as an output switch.  it should also sense if the connected «consumer» is turned-on or off and report to the administrator at the other end of the phone line.  The administrator would then call-in the device, log in with the password, and check the state of «consumer», turn it on or off, change password or some other settings.  Current version has only one relay.  __ 

Phone line in use indicator -  With this circuit you can monitor your telephone line.  You are able to detect if any telephone in the same line is busy with the help of a LED.  This circuit does not affect the telephone’s line provider, so it’s trouble free but you use it at your own risk.   it connects in parallel with the telephone line.__ 

Phone line indicator -  Schematic only __ Contact IQ Technologies

Phone Line In-Use Indicators -  Presented are two different designs that perform the same function.  Each circuit lights an LED when a telephone line is in use, and can be placed at extension telephones to alert others not to interrupt.  Unlike "off-hook" indicator circuits, these circuits do not have to be inserted in series with the telephone; they are simply plugged into the telephone line to provide an indication that one or more of the phones on that line are being used.  Both circuits are powered by 9v batteries, and therefore present little danger of imposing an unsafe condition on the telephone line or equipment.   __ Designed by Arthur Harrison

Phone Line Polarity Checker -  Do you suspect your broadband speed (DSL) is slower than it should be? it could be as simple as incorrect polarity in your phone wall socket.  Build this very cheap, very simple device to find out whether you need to change your wiring! __ SiliconChip

Phone Messager -  I always keep one totally self powered phone (the way they all used to work) in case of a power failure.  This device works the same way, taking all of its power directly from the phone line. __ Designed by Luhan Monat-Mesa Arizona

Phone rang indicator light -  This, will detect the ring signal, energize the relay which latches up, and the LED comes on and stays on till you push SW.   __ Designed by Massoud Ajami

Phone Recorder -  This recorder can be connected to the telephone lines just about any place, and no external power source is needed.  The tape recorder's 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 there's usually about 50 Vdc across the phone thats divided over R1, R2, and R4, so that Q1's base is negative enough to keep the recorder off.  Pick up the receiver, and the voltage drops to 5 V__ 

Phone recorder -  How many times have you wished that you recorder your recent telephone conversation? I have, many many times.  So I finally decided to make this happen by using PC and a piece of hardware (powered from USB) to record audio from phone line to MP3__ 

Phone Ring -  This project has been specially designed to introduce you to SMD (Surface Mount Devices).  Surface Mount is really not new.  it started as far back as 1940 with a hybrid circuit in a digital watch.  A chip was cemented onto a slab of ceramic material.   __ Contact Collin Mitchell

Phone Screener with Voice -  This unit is an upgrade of the previous phone call interceptor.  instead of using an answering machine to provide the outgoing message and recording functions, it uses the iSD4004 (from Windbond Electronics).  The iSD4004 records up to 8 minutes of audio.  I use the first several seconds for outgoing message prompts__ 

Phone Screener with Voice -  PIC  Project  This unit is an upgrade of the previous phone call interceptor.  instead of using an answering machine to provide the outgoing message and recording functions, it uses the iSD4004 (from Windbond Electronics).  The iSD4004 records up to 8 minutes of audio.  I use the first several seconds for outgoing message prompts.  The remaining time is used to record up to 30 messages, depending on message length.   __ Designed by Luhan Monat - Mesa Arizona

Phone Tap -  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)  __ Designed by Aaron Cake

Phone Transmitter -  This small phone transmitter will transmit a phone conversation to an FM radio on the 88-108MHz band.  it uses energy from the phone line to transmit the signal about 100 meters away.  it uses the phone wire as the antenna and is activated when the phone is picked up.  Transmitter components are mounted on a small PC board.  PC layout is included.__ 

Phone USB charge hack -  iphone, ipad, HTC phone, how to charge via home made charge cable  __ Designed by Thomas Scherrer OZ2CPU

Phone wire, RJ-11 jacks & optocouplers build a bus -  12/07/04  EDN Design Ideas:  Although cutting-edge technology reaps publicity, the real world often runs on modest hardware that's just "good enough" for home automation, alarm systems, and equipment-monitoring applications.  Figure 1 shows a low-speed, multidro __ Circuit Design by Ernie Deel, EFD Systems, Marietta, GA

Phone-line-voltage Monitor meets FCC specs -  19-Aug-04 EDN Design Ideas:  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 ph __ Circuit Design by Brad Peeters, Theta Engineering, Costa Mesa, CA

Phones as Intercoms -  I have recently thought about this and come up with a kludgy but workable scheme.  Talking over the phones is easy.  You put DC current through the phone and it transmits and receives audio.  So two phones and a current source (about 25mA) all in series will give you a talking circuit.  A suitable current source can be as simple as a 9V battery and a series resistor whose value is adjusted (with both phones offhook) till about 25mA flows.  You can then bypass the battery and the resistor with a capacitor to couple the audio straight across and get a loud __ Designed by FromMarkus Wandel

Phonome: Call, Listen & Switch Devices On & Off -  Simple device that lets you call home, switch devices on and off and listen for any sounds.  There's no connection to the phone line.__ SiliconChip

PIC based Caller ID -  Caller Line identification displays on a (2x16) LCD the phone number of the person who is ringing you, before you even answer, this number stays on the LCD till it will be replaced by a new received phone number or if the button is pressed.  __ 

PIC Security System Dials Your Cell Phone -  Do-it-yourself phone dialer security system calls your cell phone, office etc.
whenever a door or window is opened, or panic button is pressed.  Great Home Alarm. __ Designed by Bill Bowden

Playing a MAC through a Standard Telephone Line -  how to get sound from computer to Telephone line__ 

Power Bank for Smartphones -  This power bank can be used for charging smartphones.  The circuit uses two integrated modules and a lithium-ion battery.  The first module is a lithium-ion battery charger and the second is...__ Electronics Projects for You

Privacy -  A privacy circuit allowing one telephone exclusive access to the line.   __ Designed by Andy Collison

Programmable path navigator Robot -  The project achieves complete concept, design and development of a programmable path grid navigator robot.  The project deals with the design and development of the mechanical, hardware, embedded software and the user interface (for path feeding) aspects of the robot.  The developed robot is a fully functional wireless robot.  __ 

Protects Phone Line from Lightning Strikes -  To build a circuit that will help protect your equipment from lightning strikes on the phone line.  This circuit was actually designed to reduce or eliminate a very local broadcast AM radio stations signal from bombarding my parents telephone line, however it also turned out to be a really good lightning protector.  __ Designed by Kevin Custer  W3KKC

PTT and soundcard interface for the TM255/455 -  Ham Radio - Modems and Soundcard interfaces __ Designed by Guy Roels ON6MU

PTT and/or soundcard interface -  Ham Radio - Modems and Soundcard interfaces __ Designed by Guy Roels ON6MU

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Telephone Circuits:   #'s - B       C - F       G - K       L - Q       R - S      T - Z


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