Phone Circuits
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The dc voltage present on a telephone line is usually around 45 to 50 V on-hook and 6 V off-hook. This circuit uses This drop in voltage to activate a relay. The relay controls a cassette tapeTecorder... -
When an asterisk * is pressed on the touch-tone phone, TCI a DTMF decoder, controls on-hold logic. Audio from the FM receiver IC4 is.placed on the telephone line when a hold condition is present. RY2 is a DPDT 12-V relay. To place a caller on hold,.. -
This system will alert you or anyone chosen by automatically dialing a programmed phone number. This is accomplished by monitoring an open- loop or closed-loop sensor switch located in the protected area. Mien the sensor detects a problem (such as a.... -
Using a Motorola MC34118 speakerphone IC, this adapter can be used with a regular telephone to provide speaker capability. This device is powered from the phone line, but it can be powered via an external power supply if the line loop current is marginally.... -
The cireiilt is built around a couple of low-cost ICs: an H11C4 optoisolator/coupler with an SCR output (Ul) and an LM3909 LED flasher (U2). It is connected to the phone line in the same manner as any extension phone. A ring signal on the telephone.... -
Two hybrids (Tl and T2) are used to allow direct connection to a telephone line. This circuit uses the common speech-inversion algorithm where the frequency of an audio signal is inverted about a center frequency. .. -
This circuit dials a stored DTMF tone sequence from EPROM when a control line is taken to 0 V. ICl is a Schmitt trigger oscillator, running at around 2 Hz. It clocks a 4024 binary counter. The counter`s outputs connect to the address leads of the EPROM. A.... -
Section Ul-a is configured as a high-gain inverting voltage amplifier that is inductively coupled to the phone line via LI. Inductor LI is a homemade unit that consists of 250 turns of fine, enamel-coated wire that is wound on an iron core. The op amp.... -
The LED indicates the status of a remote telephone. The light is off if the phone is hung up. It shines steadily if the phone is off hook, and it flashes on and off while phone rings and for 5 seconds after ringing stops. The flashing oscillator operates.... -
This system uses a transmitter at around 100 kHz (see Fig. 86-3(a)) to control a remote rece.. -
This device allows you to control remotely any (with suitable add-on expansion boards, up to eight) device, such as lights, water heaters (boiler), air-condition, plant watering, alarms, etc via a relay. By using it you can for example water the garden at.... -
The device is a dc switch that is normally on via the forward biasing of Ql via R3. Ql now clamps Q2 into a forward state by biasing its complement well into a saturated state via R4. The dc switch is turned off via a negative voltage above that of the zener.... -
A small neon lamp is triggered into conduction by the telephone's ringing voltage, passes just enough current to activate the LED in optocoupler Ul, which in turn triggers the 6-A Triac that controls 12—a 117-Vac lamp or bell. (Capacitor Cl is necessary.... -
The XR-T6425 Speakerphone IC makes it possible to carry on conversation without using the handset, while the user is talking into a microphone and listening from a loudspeaker. It is ideal for hands-free conference calls. .. -
The XR-T5995 Speech Network is a monolithic integrated circuit specifically designed for implementing a low cost telephone circuit. .. -
IC-1 and the associated circuitry form a stable audio tone generator that feeds a buffer amplifier, Ql and Q2. The tone output is taken from the emitters of the transistor pair to supply a carrier voltage for a balanced modulator made up of four diodes—Dl.... -
A simple phone automatically shows the recording circuit. In this circuit, after the call Ming sound start switch K is turned on by the sound of automatic message HFC5209D. .. -
Chaolitong Phone Travel Charger for Motorola to 308,328,338 and 368 series mobile phone battery. The charger has a nickel-cadmium, nickel hydrogen, lithium-ion battery switch, .. -
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. When the phone is not in use, a green LED.... -
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.... -
Sometimes caller might want to preserve his privacy so that his/her number is not send to the called person. Legistlation say that caller must have some way to disable sending of the called ID information when he/she wants to. This can be done by dialling s.... -
CallID Unit based on Motorola MC68HC11A1P & MC145447P chips compatible with the standard protocols. if you got a multimeter and a phone you can start testing. Check the voltage across the pair, should be 48VDC in US, 60VDC in Europe. Place a 600 ohm....
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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. The device must be placed a few centimeters from the cellular phone, so its sensor coil L1.... -
The circuit in Figure 1 adapts a small key-chain voice recorder to the Tip and Ring lines of a phone line that has been disconnected from the central office. The purpose is to play a prerecorded message into any phone on the line when its receiver goes....
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I have used this type of circuits for quick testing of telephone equipment. This is a quick hack that does not exactly resemble the characteristics of the real telephone network, but is enough for this kind if applications. If you want better simulation,....
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For this scheme to have satisfactory signal-to-noise and frequency-response parameters, the clip, connecting cable, and amplifier must m be attached parallel to the signal wire and must be as long as is conveniently possiblean inch or moreand preferably....
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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.... -
This self-build project can simulate a telephone call / connection between any two local telephone devices. This for a fraction of the outlay of some commercial units, many with cost-increasing features that usually are not required. The circuit is centred.... -
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 in Figure 1 shows a method of meeting this challenge with 100% margin. In other words, it presents approximately 10-M leakage resistance across the line. The basic relaxation oscillator has the LED of an optoisolator in the discharge path of the....
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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.... -
This project displays telephone numbers decoded from tones. A microphone picks up the tones, a preamplifier boosts the signals, an SSI-202 DTMF chip decodes the tones, a Basic Stamp acts as an interface to an LCD display and also provides "RS-232" serial....
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This project fits more for custom made battery casing that can have more space to hide things inside. This switch with few alterations can be used for any other project as well but is designed based on e-bike needs! This project use a clever functionality of.... -
The circuit described here uses ultrasonic oscillations and operates based on the propagation velocity of these oscillations in the air. Thus, we can easily determine the distance of two points if the time within which the wave travels this distance is.... -
Sometimes the precious metals are hidden too deep and are not detected except with complicated devices. In many cases, however, small pieces of precious metal buried near the surface can be detected by relatively simple means. Everyone is very attractive to.... -
Many times for various reasons we forget or can not water the plants that we have in our homes. And many humidity sensors units just notify us with a beeping sound or with a flashing light, that the pot needs watering. But what if we are away from home? This.... -
The principle behind a metal detector is really very simple. Proof of this is the circuit that follows, in which it proves that the construction of a metal detector can be done in the minute, with few components that we find very easily everywhere. With the.... -
The sub-harmonic bass generator is a sound producing unit for guitars. The sound it produces looks very much like that of the bass guitar. The octave generator is sometimes quite unusual since it does not produce any of the usual ways of coloring the sound,.... -
In the past the sounding (sea bottom measurement) was done with the "bullet", that is, with a heavy lead object that the seamen plucked into the sea hung from a calibrated rope. As soon as the "bullet" reached the bottom, the depth appeared directly from the.... -
This Amplifier was designed to have the following specifications: Distortion less than 0.1% at full power of 100W even at 20KHz. Power has to be attributed to an extended bandwidth. The output transistors must be protected against short circuits. The power.... -
A series of LEDs serve to alert the gardener when plants need water. Using two conventional digital integrated LEDs and a series of LEDs, we make a very useful device for gardening. The device detects the amount of water in the pot and alerts the grower.....
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