 Telephone In-Use Relay Controller
Telephone In-Use Relay Controller circuit diagram
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.
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.
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.
Telephone Headgear
Acompact, inexpensive and low component count telecom head- set can be constructed using two readily available transistors and a few other electronic components. This circuit is very useful for hands-free operation of EPABX and pager communication.
Smart Phone light
The circuit shown here is used to switch on a lamp when the telephone rings, if the ambient light is insufficient.
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.
Cordless phone backup
Here is a simple circuit which can be used with cordless phone SANYO CLT-420 or similar sets.
Multipurpose Circuit for telephone
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.
Conversation Recorder
This circuit enables automatic switching-on of the tape recorder when the handset is lifted.
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.
Telephone call meter using calculator
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.
Having secrecy in parallel telephones
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 overloading and overhearing of the conversation by an undesired person. In order to eliminate all such problems and get a clear reception, a simple scheme is presented here
Telephone line based audio muting and light
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.
Two line intercom plus
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.
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.
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.
Audio Visual Indicator for Telephones
Many a times one needs an extra telephone ringer in an ad joining room to know if there is an incoming call.
8 Line Intercommunication using 89c51
This project is aimed to make the low cost intercom system by which eight telephone lines can be interfaced with this hardware.
Telephone Hold Button
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.
Ringing Phone Light Flasher
This circuit is extremely simple, therefore there is less chance of any problems. It can be placed anywhere on the phone line and it will record any conversation on any phone on that line.
Phone Busy Indicator
Have you ever been using the modem or fax and someone else picks up the phone, breaking the connection? Well, this simple circuit should put an end to that. It signals that the phone is in use by lighting a red LED.
Cut Phone Line Detector
When the circuit detects that a phone line has been cut, it activates a MOSFET which can be used to drive a relay, motor, etc. It can also be connected to a security system.
Telephone amplifier
While talking to a distant subscriber 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.
Soft Musical Telephone Ringer
The normal telephone bell, at times (specially during night when one does not want to be disturbed), appears to be quite irritating. The circuit shown here converts the loud sounding bell into a soft and pleasing musical tone.
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.
Cellular Phone calling Detector
This circuit was designed to detect when a call is incoming in a cellular phone (even when the calling tone of the device is switched-off) by means of a flashing LED
Telephone line monitor
This nifty little circuit lets you record your phone conversations automatically
Ringing Phone Light Flasher
Makes your 220/110V bulb flashes when telephone rings. Can be very useful when you need silence, or just want to have strange phone :)
FM Telephone Bug
Extremely easy to build and very useful transmitter
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