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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. Points X and Y in the circuit are connected to the telephone...
Telephone In Use Indicator Circuit
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...
DTMF Tone Decoder
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 output. If you`d like to build your own tone decoder "from scratch", read on: You might have...
Interface between Ericsson 6xx/7xx phones and a PC
This interface is needed to connect the phone to a PC, because the PC`s serial port works with voltage levels between -12 and 12V (RS232 protocol) and the phone operates between 0 and 5V (TTL protocol). Don`t even think in conecting your phone directly to the serial port, this would certainly damage your phone and/or the PC serial port!!! The...
Isolated Telephone Interface
There`s not much to this circuit. The two RJ-11 jacks are set up to feed the telephone circuit through from the wall to the phone. The active signal for a single phone is on the red and green wires. Yellow and black are usually used for a second phone line. The 0.22uF capacitor blocks any DC current from flowing through the transformer. The 4.7K...
The Link Telephone Intercom
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). The Link is designed to enable one call at a time within a small area (about 100 meters from the black box is about the max per handset)...
Low-Cost PCO Billing Meter
In the circuit shown in Fig. 1, when the handset is off-hook, the optocoupler MCT2E (IC1) conducts and forward biases transistor T1, which, in turn, forward biases transistor T2 and energises relay RL1. In energised condition of relay, the upper set of relay contacts connects the positive supply rail to PLL (phase-locked loop) IC2 (LM567) pin 4,...
Modem-access adapter reduces interference
The design also overcomes the shortcomings of modem interference protectors. The design eliminates mutual interference between phones and modems, is compatible with the line-usage indicators on multiline phones, can search for an idle phone line in multiline installations, draws minimum power, and requires no changes to a PC modem`s hardware or...
One important feature of this circuit is that the circuit derives its power directly from the active telephone lines, and thus avoids use of any external battery or other power supplies. This not only saves a lot of space but also money. It consumes very low current from telephone lines without disturbing its performance. The circuit is very...
Phone wire, RJ-11 jacks and optocouplers build a bus
This version of the familiar current loop offers a simplified and somewhat novel implementation in which optocouplers serve triple duty as level converters, isolation/protection devices, and bus interfaces. Galvanic isolation avoids ground loops, increases the effective communications range, and adds a measure of protection for attached...
Radio Remote Control using DTMF Circuit
This circuit differs from similar circuits in view of its simplicity and a totally different concept of generating the control signals. Usually remote control circuits make use of infrared light to transmit control signals. Their use is thus limited to a very confined area and line-of-sight. However, this circuit makes use of radio frequency to...
This is the lowest cost dialing alarm on the market and shows what can be done with an 8-pin microcontroller. The complete circuit is shown below. You cannot see all the features of this project by looking at the circuit - most of them are contained in the program. So, read on and see what we have included. Dial Alarm-1 has a single input...
Phone line indicator using BF256B
With this circuit can determine whether any of the phones of the same line is busy (it's up the handset), with the help of a LED.To circuit has no measurable effect on the telephone, so that there are problems with phone line company . The circuit is connected in parallel with the two wires of the telephone line. The bridge rectifier (D1. .. D4)...
Isolated Telephone Interface
This circuit allows you to record audio from a telephone line into a tape recorder or computer soundcard. Most of the parts for this circuit can be scrounged from an old modem, with some work, it is possible to rewire the modem circuitry and use the old modem case. Note that some countries have laws that require the user of a phone recording...
Cut Phone Line Detector
A while ago I got an email asking for the schematic of a circuit to detect cut phone lines. It didn`t take me long to find this circuit in Electronics Now. 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.
ADSL Splitter Adapter
This really isn't much an electronics project as it is a telephone wiring project. Take note that this proejct involves connections to telephone lines. This may be frowned upon by your telephone service provider, AKA The Telephone Company. Always use proper telephone components for the area in which you live. It is your responsiblity to...
Line Powered Phone Messager (PIC16C819)
The phone company provides 3 levels of power. With no devices 'off hook' the line rests at 48 volts DC. If you draw any more than a fraction of a milliamp or so, you get the phone company's attention and a dial tone. When the line rings, you get about 100 volts (rms) of AC signal on top of the 48 volts DC for 2 seconds on and 4 seconds off. The...
Phone Call answering machine (PIC16F870)
The PIC16F870 chosen for this project has seval analog channels. One of these is used to capture the DTMF tones and decode the digits. The actual phone connections are made using a 'hacked' 5 line expandor from Radio Shack. This device connects between the phone line, an answering machine, and your phones. When a phone call comes in, the...
Phone digital answering machine
This unit is an upgrade of the previous phone call interceptor. Instead of using an answering machine to provide the outgoing message and recording functions, it uses the ISD4004 (from Windbond Electronics). The ISD4004 records up to 8 minutes of audio. I use the first several seconds for outgoing message prompts. The remaining time is used to...
Phone Line Simulator with PIC16F819
Creating projects that connect to the phone line can be a real chore without some device like this. It generates the 48 volts DC for the on-hook condition, the 100 volts AC for the ring signal, and the 20 milliamperes DC for the off-hook condition. To use the device, a phone is connected to the left jack. When it is picked up (off-hook), a ring...
Dual phone line auto recorder
Many times exists the need recording some conversations from a telephone line and this it's relatively easy. If we want however to have the possibility recording from two telephone lines simultaneously in a tape recorder, we needed a circuit as what appears in the Fig.1. The circuit stimulates when earphone from a telephone unit is raised,...
Phone Line In use LED
If we have a lot of parallel telephones on a telephone line, we needed a unit that will have the possibility of showing if somebody of the telephone has raised the earphone. Our this possibility give the circuit. The circuit is connected at parallel with the two cables of telephone line. The bridge of rectification D1- D4, protect and ensure the...
Telephone Line Controller
A very simple circuit, that will find application in the case where you have a lot of telephones installed on a telephone line and would want to know if somebody of them is open. Thus you will not be off any discussion. Simultaneously it can cut the certain sound from stereo amplifier that are in high volume, the sound of some television or...
Telephone Hold Line
The UNIVERSAL HOLD circuit detects the dual tone, multi frequency (DTMF) tone that is generated when the # key is pressed and then activates a circuit that partially loads the telephone line so that the central office thinks a phone is still off hook even after it is hung up. When any phone is again picked up, the hold function is canceled.
Advanced Phone in use circuit
This project has two features. It will let you know when a single phone is using the line and also when two phones are on the line! The green LED indicates the first phone and the red LED indicates the second phone! There are many times when you need to know the state of the phone line and this project will prove to be invaluable. It will...
Phone Line status indicator
R1 and R2 form a voltage divider, insuring that the phone line sees a high impedance load and that high voltages (such as the ring voltage) are easily dissipated by the protective diodes (CR1 and CR2). Also (obviously) they serve to divide all incoming voltages by two. Capacitor C1 filters out some of the audio signals that might otherwise make...
Telephone line interfacing
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...
Telephone Remote control
Here is a teleremote circuit which enables switching on and off of appliances through telephone lines. It can be used to switch appliances from any distance, overcoming the limited range of infrared and radio remote controls. The circuit described here can be used to switch up to nine appliances (corresponding to the digits 1 through 9 of the...
Cordless phone backup circuit
Normally the base of a cordless phone has an adaptor and the handset has Ni-Cd cells for its operation. The base unit becomes inoperative in case of power failure. In such conditions, it is better to provide a backup using Ni-Cd cells externally. Here is a simple circuit which can be used with cordless phone SANYO CLT-420 or similar sets. The...
Telephone DTMF decoder 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...
Telephone Headphone amplifier
A compact, 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. Since the circuit draws very little current, it is ideal for parallel operation with electronic...
telephone line loger
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...
Telephone Ringer Circuits
Telephone Surveilance Bug Circuits
Ultrasonic distance finder circuit
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 measured. There are three main categories of distance measurement methods in use: a) By...
Simple Metal detector circuit with CD4030
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 find something potentially valuable, hidden a few centimeters below the soil. So many...
Fully automatic watering circuit for flower pots
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 circuit comes as a solution to this problem. Depending on humidity of the pot at...
Simple deep searching metal detector circuit
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 circuit of this metal detector, it is possible to detect a metal coin in depth of 90 to...
Sub-Harmonic Bass Converter for Electric Guitars
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, such as filtering or distortion. Instead, a frequency division system produces outputs...
Echo Depth Sounding Sonar for Boats
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 calibration of the rope. This arrangement still exists in some yachts. The big...
100W HiFi Audio Amplifier Circuit
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 supply must be symmetrical so that no electrolytic capacitors are needed at the outlet....
Plant-Pot Water Level Indicator Circuit
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. The circuit of the device is shown in Figure 2. The water detection is made from the bottom...
Analogue Sound Preasure dB-Meter Circuit
The best human ear can capture sounds from 20Hz to 20KHz. These limits are known to be the broadest that can exist. Normally the normal limits range from 100Hz to about 13KHz and depend on the age and health of the individual. We for our measurements and to have a good accuracy we will get the limits of 20Hz to 20KHz. A sound to be heard does...
DIY HV Variable Capacitor
DIY PMA Alternator Plans
Digital Signal Integrity