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Speech activity detector for telephone lines
The circuit can be used in telephone lines for speech activity detection purposes. This detection is very useful in the case of half-duplex conversation between two stations, in the case of simultaneous transmission of voice and data over the same pair of cables by the method of interspersion data on voice traffic, and also in echo suppressor...
Dual tone decoding
Two integrated tone decoders, XR-567 units, can be connected (as shown in Fig. 1A) to permit decoding of simultaneous or sequential tones. Both units must be on before an output is given. R1C1 and R'IC'l are chosen, respectively, for Tones 1 and 2. If sequential tones (1 followed by 2) are to be decoded, then C3 is made very large to delay...
Telephone hold button
The on-hook (no load) voltage across the red-green wires will be 48 V or slightly less when all telephones are on-hook (disconnected). When any telephone goes off-hook the load current flowing in the telephone causes the voltage to fall below 5 volts dc. Although the telephone hold is connected across the red-green wires, silicon control...
Telephone-controlled tape starter
This circuit converts a tape recorder into a completely automatic telephone conversation recording instrument that needs no external power source. Voltage at the switch terminals of tape recorder applied to a pair of Darlington-connected transistors, Ql and Q2, will turn on and start the tape recorder. To turn the transistors off, and thereby...
Transistor Ql of the headset amplifier circuit amplifies the 30 mV signal, that would have gone to the earphones, to .5 V. which sufficiently drives the stereo earphones. Capacitor Cl blocks any de current from shorting back into the telephone base. Capacitor C2 provides the very important ac signal short around the amplifier. Capacitor C3...
This circuit shows the TP5700 directly interfacing to a low-voltage DTMF generator. VREGt supplies the necessary 2-V minimum bias to enable the TP5380 to sense key closures and pull its mute output high. VREGt then switches to a 3-V regulated output to sustain the tone dialer during tone generation. The TP5700 DTMF input incorporates the...
This circuit consists of two audio channels, a control circuit, and a hybrid irlterface circuit. The gain of each audio channel is conÂ· trolled by the control circuitry, with the use of a voltage controlled amplifier (VCA). The inputs to the control circuit are obtained from each of the audio channels. The hybrid interface circuit performs...
Here is a simple method of series connection into the telephone set suitable for PABX or short line applications. When the telephone handset is lifted, Cl is charged via D1 to (Vz1 -0.7) V and DF320 power on reset occurs. When the first keyed digit is recognized, Ml goes to logic 1, muting the telephone network by switching on the low on...
The oscillator is a Motorola MC14410CP chip using a 1-MHz crystal. The chip generates both the high and low tones, feeding the energy to the amplifier through 1-K resistors and the 1-I"F capacitor. Values for the output resistors can vary from a few hundred 0 to about 60 KO. The value of the resistor shunting the crystal can vary from about 3...
The TP5700 or TP5710 can reduce the number of components required to build a pulse-dialing telephone, as shown. The usual current source can be eliminated by using the VREGl output to power a TP50982A low-voltage (1. 7 V) pulse dialer via a blocking diode. A low forward-voltage drop diode such as a Schottky type is necessary because VREGl is...
When the handset is lifted and power is applied to the circuit, Q2 is fed base current through R2, which in turn drives Ql. C2 is charged via R3 in series with D1 to (Vz1 -0. 7) V. When the minimum operating Vnv voltage is reached, power on reset occurs via the rc network of Cl and RS. Q2 is maintained in the on condition by Gl, while Q3, and...
A sensitive-gate SCR provides a line-holding current of 20 to 40 mA, depending on loop resistance. It also lights an LED to give the user a positive indication that the telephone line is on hold. The 20 to 40 mA should prove sufficient to hold the majority of lines, but it might require increasing-by decreasing the size of Rl-in individual...
This encoder uses a single contact per key keyboard and provides all other switching functions electronically. The diode connected between terminals 8 and 15 prevents the output from goitrg more than 1 V negative with respect to the negative supply Vss. The circuit operates overthe supply voltage range from 3.5 V1o 15 Von the device side of...
This indicator senses the switching on and off of the 48-V de line voltage and transmits the pulses to logic circuitry. An Hl1A10 threshold coupler, with capacitorfiltering, gives a simple circuit which can provide dial pulse indication, and yet reject high levels of induced 60-Hz noise. The DHD805 provides reverse bias protection for the LED...
The telephone-line decibel meter and line-voltage sensor shown lets you accurately monitor and adjust telephone sound levels. The 600-0 resistor properly terminates the line.
This circuit can be used in telephone lines for speech activity detection purposes. This detection is very useful in the case of half-duplex conversation between two stations-in the case of siroultaneous transmission of voice and data over the same pair of cables by the method of interspersion data on voice traffic, and also in echo...
This circuit is a bidirectional amplifier that can amplify both signals of a duplex telephone conversation. It uses the principle of negative resistance. Obviously, such an amplifier could easily be unstable; however, you can adjust Rl for maximum amplification and the circuit will remain stable.
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...
Each and every time a phone on the same line or calling numberis taken off-hook, the circuit will be activated to control an external electronic circuit. If several extension telephones are used on one phone line, the circuit can be useful as a busy indicator. LEDl contains a special flashing red LED that makes an excellent indicator for a...
Q1 and Q2 are used to form the basis of an interface circuit for attaching a cassette recorder to the phone line. The circuit does not require a power supply because operating power is drawn from the telephone line itself. The incoming signal is fed across a bridge-rectifier circuit, consisting of diodes D1 through D4. When the phone is on...
The IR transmitter connects to a telephone cir cuit, and transmits both sides of all telephone conversations to any line-of"sight location, within 40 feet. No !fOWer 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, thereby keying their equipment. We...
Audio from the telephone is inductively coupled to the base of Ql. which is used as a preamp. The preamp provides a gain of about 75 dB, to boost the input signal from .about 4 mV to about 300 mV pk-pk. If you use a higher gain transistor, increase the value of R9 to produce a Q point, measured from minus to the collector of Ql, of one-half...
Amplify or record a telephone call with the simple circuit shown. The 8-0 secondary winding of a miniature transistor output transformer is connected in series with either of the telephone lines.
Telephone-Operated Ac Power Switch
Tones (from the DTMF) on the telephone line are detected by Ul. When a valid tone is received, pin 14 (D
Telemonitor For Recording Phone Calls
This circuit switches a tape recorder via PL2. When on-hook, D5 conducts, turns on Ql, and cuts off Q
Phone Message Flasher
This circuit flashes an LED to indicate that your phone rang during your absence. A differential amplifier with hyste
If you are busy and cannot answer or do not wish to answer your phone, this circuit will give a busy signal without you
Telephone Auto Record
The circuit requires neither a battery nor an ac supply to make it work. Set the recorder to the record position and
This accessory connects to phone and will activate an attention-getting 120-V bell whenever a ringing voltage appears on the ph
The circuit receives its power from a 15-V wall adapter (not shown). The circuit takes advantage of the fact that th
Fax Mate Circuit
The fax mate separates the fax machine from the phorie line, rings the fax machine on command, connects equipment to incoming lines, and senses the end of the message. When a touch tone pound signal (#) is detected, it actuates a ring greater and driver for the fax macliirie (the # signal is not used in ordinary dialing). The connect signal is...
Telephone Call Recording Circuit Circuit
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.
Telephone Ringer Circuits
Telephone Surveilance Bug Circuits
Construction of 50Watt 8Ω two-way Hi-Fi Speakers
The presented speakers are distinguished for their small dimensions and their extraordinary sound. Our home space is often limited and prohibitive for large speakers. This limitation does not mean that we will stay without high Sound Quality. Its design is simple, low cost and is easy to construct. Speaker types are too many and are designed in...
GSM modem circuit with Wavecom WMOi3
Modems are devices that connect either remote devices to a computer, or two or more computers to each other. Their connection is usually wired. The GSM modem we present is wireless. It can connect two computers, a computer with the internet or even be the central unit for a data acquisition system. Generally the construction is a GSM phone...
1W UHF Linear Amplifier with BLW33
This circuit is an amplifier for small transmitters operating in the UHF band, specifically in the 450-800MHz range. The amplifier works in class A and we used the well-known Philips BLW33 transistor for its manufacture. The construction, although simple, can be said to be quite critical due to the high frequency singularity. To achieve this, a...
8W Amplifier with TDA2003 circuit
Many times a small amplifier is needed to meet the needs of small spaces. This amplifier can be either mono or stereo, with this circuitry you can comfortably drive two small speakers. To build the amplifier you do not need anything but a few materials and a small power supply. The power of the amplifier, although low power, will solve many...
FM Linear Amplifier 400mW
This amplifier is intended for amplifying low signals from oscillators in the FM band. It does not have frequency regulators with variable capacitors and coils, it has a wide range and moderate power capable of driving several linear amplifiers. The whole construction is based on the two low-power 2N4427 transistors, which are designed for the...
50 Watt Hi-Fi power amplifier circuit
SGS Thomson's integrated TDA7294 is a high-frequency acoustic power amplifier, with true high-precision specifications, suited for all relevant applications. Its main feature is much higher output power than is usual in amplifiers with similar distortion performance. According to its manufacturer, the output stage of this 15-pin integrated can...
RF Remote Control Switch Rx-Tx circuits
This circuit consists of a 2048 radio remote control transmitter and the corresponding wireless receiver with very high reception sensitivity and low consumption. The combination of the two above gives a high-reliability remote control, ideal for security systems, alarms, automation, etc. At home, in the car and elsewhere. Using the wireless...
0-30V Lab Variable Power Supply
At the left side (input AC) goes the secondary of a 220 volt (primary) 18 Volt (secondary) / 3 Ampere mains transformer. The alternating voltage of 18 volts from its secondary transformer is rectified by the diodes D1, D2, D3 and D4, which are connected to a bridge arrangement and make a double rectifier. The pulse from the bridge exit is...
Ultra High Sensitivity Metal Detector Circuit
This circuit is a metal detector capable of detecting large metallic objects. at a depth of 2m to 3m. It depends on the size of the object, and often on the type of soil. Construction is very easy to implement even for a beginner. The necessary components are easy to find everywhere. This detector has the ability to detect a gold coin of 20mm...
Digital Signal Integrity
Interconnection and Timing of Digital Circuits
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