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Telephone Circuits, Page 6
Telephone Circuits:   #-A    B-C    D-F     G-N      O-S     T-Z
Last Updated on: Friday, October 03, 2014 10:38 AM


Links to electronic circuits, electronic schematics, designs for engineers, hobbyists, students & inventors:

Talking Phone Dial Monitor -  Speaks the numbers that you dial as you dial your telephone. 5 pages. Not available as a kit of parts. [free schematic from Golab.com]
Taxi Phone Automatic Dialler -  (circuit / design added 8/03)
TCP/IP Library Programmer's Guide -  Silicon Labs Application Notes....[App Note]
TDR Reflectometer -  (electronic schematic / circuit added 4/02)
Telecard reader -  This telecard reader can read the contain of any  telecard until 64 bytes ( 512 bits ) and display it  to  hyper terminal software, using RS232 port.….(design added 05/09) [Circuit designed by Serasidis Vasilis]
Telephone #Display -  The given circuit, when connected in parallel to a telephone, displays the number dialled from the telephone set using the DTMF mode.  This circuit can also show the number dialled from the phone of the called party.  This is particularly helpful for receiving any number over the phone lines. The DTMF signal—generated by the (added 10/05)
Telephone #Display EFYLinux -  ....
Telephone Amplifier -  While talking to a distant sub- scriber on telephone, quite often we feel frustrated when the voice of the distant subscriber is so faint that it is barely intelligible. To overcome the problem, circuit of an inexpensive amplifier is presented here. It can be assembled and tested easily. There is no extra power source needed to power up the circuit, as it draws power from the telephone line itself. The amplifier will provide fairly good volume for the telephone conversation to be properly heard in a living room. A volume control is included to adjust the volume as desired. The circuit is built around IC LM386. ….(electronic schematic added 11/08)
Telephone Audio Interface -  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 in series with the transformer line connection to prevent DC current from flowing in the transformer winding which may prevent the line from returning to the on-hook state. The capacitor should have a voltage rating above the peak ring voltage of 90 volts plus the on-hook voltage of 48 volts.... [Bill Bowden's circuit]

Telephone Autodialler -  (circuit / design added 8/03)
Telephone call meter using calculator & COB -  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 calculator enables conversion of STD/ISD calls to local call equivalents and always displays current local call-meter reading. The circuit is simple and presents an elegant look, with feather-touch (added 01/2010)
Telephone call Voice Changer -  Voice manipulation device specially intended for props 9V Battery operation  (added 05/06/07)
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 about 11 s. During standby conditions, the -28Vdc bias on the phone line maintains the....
Telephone Conversation Recorder -  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. ….(electronic schematic added 11/08)
Telephone Headgear -  A compact, inexpensive and low component count telecom headset 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. (added 10/05)
Telephone Headset Amplifier -  This circuit goes between a telephone and a headset. The project has a headset cord and plug (cut from a cheap cell phone headset) on the input and a suitable jack on the output. The speaker signal passes through this circuit, but the microphone signal is passed straight from the plug to the jack. This circuit is specifically....[Designed by Andrew R. Morris  (added 09/05)]
Telephone Hold Button (Aaron Cake) -  Although a hold feature is standard on most new phones, a lot of us still use the origional bell phones. Those of us that require a hold feature will find this circuit very useful. It is easy to build, and is compact enough to be installed inside the phone with no real problem. It is also powered by the phone line itself, eliminating the need for batteries.... [Circuit Design by Aaron Cake]
Telephone In Use Indicator -  This circuit will illuminate a LED if one of your telephones is in use. It should work in all countries (Including UK) that have a standing line voltage above 48 Volts DC…. [Miroslav Adzic]
Telephone in Use LED Indicator -  (circuit / design added 8/03)
Telephone in use Light -  ASCII format (circuit / design added 8/03)
Telephone in Use Relay Circuit -  Circuit to close a relay when any telephone extension is off the hook…. [Bill Bowden's circuit]
Telephone In-Use LED Indicator -  Circuit to illuminate an LED when any telephone extension is off the hook. [Bill Bowden's circuit]
Telephone in-use light -  (electronic design added 6/07)
Telephone Line Audio Interface - This device connects the telephone line to a home theater system or PA system (receiver only).  It is phone line powered and features automatic volume control (AVC).  It also mutes itself when a phone is picked up to prevent feedback. [Circuit Designed by Andrew R. Morris]
Telephone line based audio muting & light on circuit -  Very often when enjoying music or watching TV at high audio level, we may not be able to hear a telephone ring and thus miss an important incoming phone call. To overcome this situation, the circuit presented here can be used. The circuit would automatically light a bulb on arrival of a telephone ring and simultaneously mute the music system/TV audio (added 10/05)
Telephone Line Based Audio Muting & Light-On Circuit -  ....
Telephone line monitor -  If you feel that somebody is tampering with your telephone line you might find this little circuit useful. It detects if there is another telephone connected to the line, if there is a short or an open line. Sound and a flashing light will tell you which is the current situation. The speaker is practically cut out during a normal conversation thus....(added 9/07)
Telephone Line Monitor (ee.washington.edu) -  ASCII format (circuit / design added 8/03)
Telephone Line Monitor (Plans) -  When the Dispatcher picks up the phone (in a standard circuit, I have NO clue what your PBX does..this will work on standard home phones, and I used to use it for a tape-recording controller) Hey, there's an Idea, spend $25 on a telephone recording device, and hitch it to a nice loud amp and speaker combo, instead of a tape deck. It'll save you loads of time....(electronic design added 6/07)
Telephone Line Vigilant -  Here is a telephone line vigilant circuit to guard against misuse of your telephone lines. It monitors telephone lines round the clock and provides visual as well as an audio warning (when someone is using your telephone lines) which can be heard anywhere in the house. Another advantage of using this circuit is that(added 10/05)
Telephone Listening Bug -  Here is a simple transmitter that when connected to a phone line, will transmit anything on that line (execpt the dial tone) to any FM radio. The frequency can be tuned from 88 to about 94Mhz and the range is about 200 feet. It is extremely easy to build and is therefore a good, useful beginner project. ….(design added 11/08)
Telephone operated remote control using PIC16F84A microController -  This design controls up to 8 devices using a PIC microcontroller (PIC16F84A) connected to the phone line. The unique feature here is that unlike other telephone line based remote control, this device does not need the call to be answered at the remote end so the call will not be charged.  This device depends on number of rings given on the telephone line to activate/deactivate devices(added 10/05)
Telephone PBX -  I've been fascinated with telecommunications from an early age. When I was twelve or so I had an intercom system from which I could talk to most of the house from my corner of the kids' room. It was made out of the amplifier from a record player, and miscellaneous parts from old TV sets. When I was fourteen someone gave me a WW2 vintage shortwave receiver with a blown power supply.... [Designed by Markus Wandel]
Telephone Power? -  ASCII format (electronic Circuit diagram added 03/03/03)
Telephone Privacy Adapter -  (electronic schematic / circuit added 4/02)
Telephone Receiver -  An interesting circuit and handy electronic telephone receiver, suited for receiving incoming calls, is described here.  This circuit can be connected to almost all types of telephone exchange lines. To simplify the gadget, the dialer section has been omitted. The circuit can be constructed on a medium size veroboard. …....
Telephone Record Control -  This circuit will allow you to connect any tape recorder that has a mic and remote input to a phone line and automatically record both sides of a conversation when ever the phone is in use.You will need to take a couple of voltage readings before connecting the circuit…. [Circuit designed by Randy Linscott]
Telephone Recorder -  This circuit lets you record your ph1-conversations automatically, notice that this circuit does not provide isolation between Telephone line and the recorder…. [The design by Aaron Cake]
Telephone Recording Circuit -  How they work and some example  (added 5/02) [Tomi Engdahl]
Telephone Recording Switch -  Switches on a Tape Recorder and records both sides of the conversation, when a phone is picked up. Useful to log all telephone conversations. (Circuit design added 7/06)
Telephone Remote Switch -  This device connects to the telephone line and can be used to remotely control up to 4 relay outputs using a DTMF (tone dialing) telephone. A number of user settings are available to improve the useability and security of the device. The kit comes complete with a small plastic case with silk-screened front and rear panels. ….(electronic schematic added 11/08)
Telephone Ring Generator using 60hz Power 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 resistor. The 70 volt/ 30 Hz ring voltage is produced from the 120 volt side of a small 12.6 VAC power transformer.... [Design by Bill Bowden]
Telephone Ring Generator using Switching Power Supply -  The telephone ring generator shown below generates the needed high voltage from a simple switching mode power supply (SMPS) which employs a CMOS Schmitt Trigger square wave oscillator, 10 mH inductor, high voltage switching transistor (TIP47 or other high voltage, 1 amp transistor) and a driver transistor (2N3053). The inductor should have a low DC resistance of 1.5 ohms or less. The switching supply must have a load connected to prevent the voltage from rising too high, so a 22K resistor is.... [Bill Bowden's circuit
Telephone Ringer by IC KA2411 -  Simple telephone Ringer with KA2411 IC. ….(design added 11/08)
Telephone Ringer using 555 Dual Timers -  Using modulated rectangular waves of different time periods, The circuit presented here produces ringing tones similar to those produced by a telephone. The circuit requires four astable multivibrators for its working. Therefore two 556 ICs are used here. The IC 556 contains two timers (similar to 555 ICs) in a single package. One can also assemble(added 10/05)
Telephone Ringer using Timer ICs -  ....
Telephone Ringing Circuits -  how to detect ringing and how to make phones ring (added 5/02)
Telephone Ring-Tone Generation -  DN134  Design Notes (Linear Technology) (app note added 2/06)
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. The 1000-W primary winding can feed either a cassette recorder or an audio amplifier....(electronic design added 6/07)
Telephone Test Circuit with Audio Mixer -  get Telephone audio to mixer or send audio to Telephone (added 4/05)
Telephone Transmitter FM -  Receive telephone conversations on any FM radio with this neat little device…. [Tony van Roon's circuit]
Telephone Voice Changer -  Although this kind of voice effect can be obtained by means of some audio computer programs, a few correspondents required a stand-alone device, featuring microphone input and line or loudspeaker outputs.  This design fulfills these requirements by means of a variable gain microphone preamplifier built around IC1A, a variable steep Wien-bridge pass-band filter centered at about 1KHz provided by IC1B and an audio amplifier chip (IC2) driving the loudspeaker. ….(electronic schematic added 11/08)
TeleRemote Control -  ....
Teletext Devices -  (circuit / schematic design added 6/06)
The Cheap But Useful Ericsson Cell Phone Display GA629 -  You used to have an Ericsson Cell Phone GA628 and you also loved it very much, however after few years of using, you’ve decided to change a brand new cell phone and you just threw it inside the drawer and never touch or look on it after that?….(added 04/06)
The KD2BD Pacsat Modem -  (circuit / schematic added 6/05)
The Link "P"-Privacy Link! (Telephone Intercom) -  ….(electronic schematic added 08/08)
The Link 4+0 – Internal Intercom -  ….
The Link A2B+1 (the Link Telephone Intercom-DTMF version) -  ….(electronic schematic added 08/08)
The Link Telephone Intercom – Every Home Should Have One! -  The Link circuitry is simple and efficient, employing just two ICs, half a dozen transistors, and a handful of garden variety components. It all runs on 12 volts and is easily assembled. You can have your own home intercom between the kitchen, the garage, the rumpus room and at your poolside ‘barby’ and all for less than $100! The “Link” intercom(added 10/05)
The Original 2 Phone Link Design -  ….
Tiny Efficient High Power LED Camera Flash Solutions for Cell Phone Applications -  Linear Technology Design Note 1009....[App Note]
Two Line Intercom Cum Telephone Line Changeover Circuit -  ....
Two Line Intercom Plus a Telephone Changeover Switch -  The circuit presented here can be used for connecting two telephones in parallel and also as a 2-line intercom. Usually a single telephone is connected to a telephone line. If another telephone is required at some distance, a parallel line is taken for connecting the other telephone. In this simple parallel line operation, the main problem is loss....(added 5/02)
Two way Simple Very Small Telephone Exchange -  …. [Site is under construction right now]
Ultra-Low Quiescent Current AF Power Amplifier -  This is an audio power amplifier, similar to what is common in transistor radios and other portable audio equipment.  This circuit however, has an ultra-low quiescent current of about 250uA, due to a unique bias circuit. I don’t even know of a chip that does that.  This circuit also has much higher open-loop gain, due....[Designed by Andrew R. Morris  (added 09/05)]
Universal Telephone Hold -  Place any phone in your house on holdeven cordless phones. 7 pages. Not available as a kit of parts. [free circuit from Golab.com]
Use Amplifier Phono Input as Line Level Input: Inverse RIAA Filter -  The circuit does two functions: signal level attenuation and inverse RIAA filtering. The signal attenuation is needed to convert the 500 mV signal to 2.5 mV signal. The inverse-RIAA filtering is needed to make the frequency response of the system flat (same equalization that is used when music is transferred to vinyl in the studio). The picture.... [Tomi Engdahl]
Use old phones as an intercom -  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 and clear connection.... [Markus Wandel]
Use old Phones as an Intercom -  ASCII format 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! (added 8/03) [richard steven walz]
Voice Record/ Playback Circuit  -  The ISD1000A is a Direct Analog Storage  device which allows you to store 20 seconds worth of voice data on an IC chip which can be play backed anytime. The data stored will stay in memory even if the power is removed. To use the circuit below simple apply power to the circuit, press the record button and hold. Speak clearly into the microphone. You have up to 20 seconds…. [Randy Linscott's website]
Voice Scrambler -  With this circuit you can modify how your voice sounds by changing the pitch of your voice.  This circuit can be connected to a phone and with a duplicate circuit on the end of the phone line, you can have a scrambled voice communication. The way the.… [Randy Linscott's website]
Voice Scrambler/Descrambler -  This is a single-inversion voice scrambler/descrambler. Though no longer useful for police scanners, it would be a fun project for a hobbyist. It was designed for use on a 9-volt battery, but by changing resistor values proportionately, it could be adapted to use whatever voltage is available in your radio.... [Designed by Andrew R. Morris]
Watch-Dog for Telephones -  Most of the telephone security devices available in market are simple but quite expensive. These devices provide blinking or beeping type line-tap/misuse indications. Quite often they do not offer guaranteed protection against unauthor-ised operation. A very simple and uni- que circuit of a telephone watch-dog to safeguard subscriber telephone lines against any fraud is described here.  This little circuit keeps continuous watch over the telephone lines and sounds an alarm in case of any misuse. In addition it transmits a loud tone through the telephone lines to prevent further misuse. ….(electronic schematic added 11/08)
Wireless Telephone Bug -  Here's a neat little project that will allow you to monitor your phone line as soon as your phone is off hook. You can use a regular FM broadcast band radio to monitor the conversation. Just remember, it ….(Circuit design added 03/08)
Wireless Telephone Eavesdropper Electronic Circuit -  The IR transmitter connects to a telephone circuit, and transmits both sides of all telephone conversations to any line-of-sight location, within 40 feet. No power is taken from the central office, as long as all phones remain on-hook. The current flows through the phone and back to the central office....(electronic design added 6/07)

Telephone Circuits:   #-A    B-C    D-F     G-N      O-S     T-Z

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