Talking Phone Dial Monitor:  (electronic (schematic / circuit added 4/02)

Taxi Phone Automatic Dialler:  (circuit / design added 8/03)

TCP/IP Library Programmer's Guide:  Silicon Labs Application Notes  (app note added 6/06)

Telephone Audio Interface:  (circuit / design added 8/03)

Telephone Autodialler:  (circuit / design added 8/03)

Telephone call meter using calculator and COB #2:  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 operation. It consumes very low current and is fully battery operated. The batteries used last more than a year.  Another advantage of using this circuit is that it is compatible with any type of pulse rate format, i.e. pulse rate in whole number, or whole number with decimal value. Recently, the telephone department announced changes in pulse rate format, which included pulse rate in whole number plus decimal value. In such a case, this circuit proves very handy.  To convert STD/ISD calls to local calls, this circuit needs accurate 1Hz clock pulses, generated by clock COB. This COB is found inside analogue quartz wall clocks or time-piece mechanisms. It consists of IC, chip capacitors, and crystal that one can....    (added 10/05)

Telephone Call Meter using Calculator and COB:  (electronic Circuit / Schematic added 10/04)

Telephone Circuits:  (electronic Circuit / Schematic added 10/04)

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. added 3/03)

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 (added 3/03)

Telephone Conversation Recorder:  (electronic Circuit / Schematic added 10/04)

Telephone Headgear #2:  (electronic circuit added 10/05)

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. (added 4/02)

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 for ultra-low battery consumption. It uses a special control circuit (Q3, Q4 and Q5) to regulate the power amplifier’s quiescent current. Also, effort was spent to design an auto-on circuit (Q10 through Q14) that draws only 1.5 uA, yet has 15mV sensitivity.   Designed by Andrew R. Morris  (added 09/05)

Telephone Hold Button #!:  (electronic (schematic / circuit added 4/02)

Telephone in Use Indicator #2:  (electronic Circuit / Schematic added 10/04)

Telephone in Use Indicator:  With this circuit mounted in or near every phone in the house, it will allow users to know if the phone is being used and not to pick up the phone. When a phone is taken off hook, the voltage across the tip and ring terminals drops to 10 volts or less. This will cause the FET (2N4360) to turn on and also turn on the transistor (2N2222). When the transistor turns on it will allow current to flow through the LED and make it light. A blinking LED could be used to make the effect better.  (added 09/05)

Telephone in Use LED Indicator:  (circuit / design added 8/03)

Telephone in use Light:  (circuit / design added 8/03)

Telephone in Use Relay Circuit:  (circuit / design added 8/03)

Telephone In-Use LED Indicator:  (circuit / schematic added 6/05)

Telephone In-Use Relay Circuit:  (circuit / schematic added 6/05)

Telephone Line Audio Interface Circuits:  Telephone recording, Telephone line to mixer and Telephone hybrid circuits (added 2/03)

Telephone Line Audio Interface:  This device connects the telephone line to a home theater system or PA system (receive 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.  Designed by Andrew R. Morris  (added 09/05)

Telephone line based audio muting and light on circuit #2:  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 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. On arrival of a ring, or when the handset is off-hook, the inbuilt transistor of IC1 (opto-coupler) conducts and capacitor C1 gets charged and, in turn, transistor T1 gets forward biased. As a result, transistor T1 conducts, causing energisation of relays RL1, RL2, and RL3. Diode D1 connected in anti-parallel to inbuilt diode of IC1, in shunt with resistor R1, provides an easy path for AC current and helps in limiting the voltage across inbuilt diode to a safe value during the ringing. (The RMS value of ring voltage lies between 70 and 90 volts RMS.) Capacitor C1 maintains necessary voltage for continuously forward biasing  transistor T1 so that the relays are not energised....    (added 10/05)

Telephone Line Based Audio Muting and Light on Circuit #3:  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:  FAIR WARNING -- THIS SITE HAS ANNOYING POP UP ADS. (added 4/02)

Telephone Line Based Audio Muting and Light-On Circuit #4:  (electronic Circuit / Schematic added 10/04)

Telephone Line Monitor #2:  (circuit / design added 8/03)

Telephone Line Simulator #1:  (circuit / design added 8/03)

Telephone Line Vigilant:  Here is a telephone line vigilant circuit to guard against mis- use 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 one comes to know of the misuse and snapping of the lines (due to any reason) instantaneously on its occurrence. This enables the subscriber to take necessary remedial measures in proper time. Various telephone line conditions and audio-visual indications available are summarized in....   (added 10/05)

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. (added 5/02)

Telephone Number Display #3:  (electronic Circuit / Schematic added 10/04)

Telephone Number 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 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 phone on dialling a number—is decoded by DTMF decoder CM8870P1 (IC1), which converts the received DTMF signal into its equivalent BCD number that corresponds to the dialled number. This binary number is stored sequentially in 10 latches each time a number is dialled from the phone. The first number is stored in IC5A (1/2 of CD4508) while the second number is stored in IC5B and so on. The binary output from IC1 for digit ‘0’ as decoded by IC1 is 10102 (=1010), and this cannot be displayed by the seven-segment decoder, IC10. Therefore the binary output of IC1 is passed through a logic-circuit which converts an input of ‘10102’ into ‘00002’ without affecting the inputs ‘1’ through ‘9’. This is accomplished by gates N13 through N15 (IC11) and N1 (IC12). The storing of numbers....   (added 10/05)

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 Power? :  (electronic Circuit diagram added 03/03)

Telephone Privacy Adapter:  (electronic (schematic / circuit added 4/02)

Telephone Receiver:  (electronic Circuit / Schematic added 10/04)

Telephone Record Control #2:  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. First determine the polarity of your phone line and connect it to the circuit as shown and then determine the polarity of the remote input and connect it to the circuit. (added 09/05)

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 (added 3/03)

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 (added 5/02)

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. (added 5/02)

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 that's 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! (added 3/03)

Telephone Recording Circuit #2:  How they work and some example  (added 5/02)

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 Ring Generator using 60Hz Power Transformer:  (circuit / design added 8/03)

Telephone Ring Generator using Switching Power Supply:  (diagram added 8/03)

Telephone Ring Tone Generator:  (electronic Circuit / Schematic added 10/04)

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. (added 3/03))

Telephone Ringer using 555 dual timers #2:  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 this circuit using four separate 555 ICs. The first multivibrator produces a rectangular waveform with 1-second ‘low’ duration and 2-second ‘high’ duration. This waveform is used to control the next multivibrator that produces another rectangular waveform. A resistor R7 is used at the collector of transistor T2 to prevent capacitor C3 from fully discharging when transistor T2 is conducting. Preset VR1 must be set at such a value that the two ringing tones are heard in one second. The remaining two multivibrators are used to produce ringing tones corresponding to the ringing pulses produced by the preceding multivibrator stages....   (added 10/05)

Telephone Ringer using 556 Dual Timers:  Using modulated rectangular waves of different Time periods, The circuit presented here produces ringing tones similar to those produced by a telephone. FAIR WARNING -- THIS SITE HAS ANNOYING POP UP ADS. (added 5/02)

Telephone Ringer using Timer ICs:  (electronic Circuit / Schematic added 10/04)

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. The1000-W primary winding can feed either a cassette recorder or an audio amplifier. (added 3/03)

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.  (added 2/06)

TeleRemote Control:  (electronic Circuit / Schematic added 10/04)

Teletext Devices:  (circuit / schematic design added 6/06)

The KD2BD Pacsat Modem:  (circuit / schematic added 6/05)

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 has been designed in such a way that you can buy parts for it ‘off the shelf’ at just about any decent electronics retail chain. It uses old pulse dial handsets and replaces the AC bell set with a 9 volt DC buzzer. The whole circuit runs from a 12 volt regulated DC supply and is suitable for short term battery operation (eg: ‘Gel Cell’). It is suitable for radio field days and sporting events (providing you can scrounge enough 4 wire cable) and may find a place in pre-schools, old folk’s homes, boy scout/girl guide halls, churches, kids’ tree houses/fortresses, or maybe even more serious uses such as small offices, factories...   (added 10/05)

Tiny Efficient High Power LED Camera Flash Solutions for Cell Phone Applications:  DN1009 -  Design Notes (Linear Technology)  (app note added 1/06)

Tiny Efficient High Power LED Camera Flash Solutions for Cell Phone Applications #2:  Linear Technology Design Note 1009 (app note added 02/05)

Two Line Intercom Cum Telephone Line Changeover Circuit:  (electronic Circuit / Schematic added 10/04)

Two line intercom plus a telephone changeover switch #2:  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 of privacy besides interference from the other phone. This problem is obviated in the circuit presented here.  Under normal condition, two telephones (telephone 1 and 2) can be used as intercom while telephone 3 is connected to the lines from exchange. In changeover mode, exchange line is disconnected from telephone 3 and gets connected to telephone 2.  For operation in intercom mode, one has to just lift the handset of phone 1 and then press switch S1. As a result, buzzer PZ2 sounds. Simultaneously, the side tone is heard in the speaker of handset of phone 1. The person at phone 2 could then lift the handset and start conversation. Similar procedure is to be followed for initiation of the conversation from phone 2 using switch S2. In this mode of operation, a 3-pole, 2-way slide-switch S3 is to be used as shown in the figure.  In the changeover mode of operation, switch S3 is used to changeover.... (added 10/05)

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. (added 3/03)

Universal Telephone Hold:  (electronic (schematic / circuit added 4/02)

Use Amplifier phono input as Line Level input:  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)..... (added 4/05)

Use old Phones as an Intercom:  ASCII format (added 8/03)

Using the TP3401/2/3 ISDN PBX Transceivers:  National Semiconductor - Application Note   (app note added 2/06)