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Alarm Phone Dialer with MT8880 and PIC 16F84A

Just hook this Alarm Phone Dialer up to something you would like to monitor, for example, a high water alarm, low temperature alarm, back window, garage door, etc. When the system is activated it will call a number of programmed numbers to let you know the alarm has been activated. This would be great to get alerts of alarm conditions from your home when you are at work. The microcontroller code is provided on the site.




DTMF Decoder

Uses MT8870 DTMF decoder and PIC microcontroller to decode telephone tones.




DTMF Decoder Using MT8870

This circuit detects the dial tone from a telephone line and decodes the keypad pressed on the remote telephone. The dial tone we heard when we pick up the phone set is call Dual Tone Multi-Frequency, DTMF in short. The name was given because the tone that we heard over the phone is actually make up of two distinct frequency tone, hence the name dual tone. The DTMF tone is a form of one way communication between the dialer and the telephone exchange. A complete communication consist of the tone generator and the tone decoder. In this article, we are use the IC MT8870DE, the main component to decode the input dial tone to 5 digital output. These digital bits can be interface to a computer or microcontroller for further application eg. remote control, phone line transfer operation, LEDs, etc...




DTMF Decoder with LCD Display

The DTMF decoder 2 is a useful tool used for decoding DTMF (Dual Tone Multi frequency) generated by telephones. The decoded digits are viewed on a 16x2 LCD screen.




DTMF Phone Decoder

DTMF tone is mainly used in telecommunication technology, such as dialing a phone number, handling various services over the telephone, as a selective choice of radio stations, etc. The individual characters are assigned to different pairs of tones. The described decoder Received characters on the LED display, and stores them in memory, where they can be retrieved later. No matter allows for some sequences of characters on and off properly connected device. In practice, the decoder can be built as in the transmitter and connected to feeder line, the transmitter can then be remotely switched on and off, or you can run such a parameter indicating the traffic reports TA in RDS. The required sequence of tones may be part of the jingle.




Extension Phone Line Switcher

Having multiple extension telephones at home is very convenient. You can make or receive phone calls practically anywhere in the house. This circuit disables other telephones connected to the phone line whenever a telephone (either the master or any extension phone) is in use. The circuit is inexpensive and is guaranteed to keep the phone conversation private. The circuit does not need an external power supply. It gets its power from the telephone line.




MT8870 DTMF Telephone Dial Tone Decoder

Today, most telephone equipment use a DTMF receiver IC. One common DTMF receiver IC is the Motorola MT8870 that is widely used in electronic communications circuits. The MT8870 isan 18-pin IC. It is used in telephones and a variety of other applications. When a proper output is not obtained in projects using this IC, engineers or technicians need to test this IC separately. A quick testing of this IC could save a lot of time in research labs and manufacturing industries of communication instruments. Here’s a small and handy tester circuit for the DTMF IC. It can be assembled on a multipurpose PCB with an 18-pin IC base. One can also test the IC on a simple breadboard. For optimum working of telephone equipment, the DTMF receiver must be designed to recognize a valid tone pair greater than 40 ms in duration and to accept successive digit tone-pairs that are greater than 40 ms apart.




Phone Audio Interface

I needed a way to extract audio from a phone line for my DTMF decoder. I found a site full of examples on how to do it, and I built an interface that suited my needs: RCA output, with a signal strong enough to be fed directly to an audio amplifier or line-in. The interface can stay connected on the line at anytime (no problems with the ring signal), and does not take of the hook. The interface must provide isolation from the line. I discovered that it can also be used to inject audio in the line.




Phone Line Controller

It might be "yet another" «device» controller that operates over phone-line, but this one works for sure :) The task was to build a device that connects to the phone line and has a relay as an output switch. It should also sense if the connected «consumer» is turned-on or off and report to the administrator at the other end of the phone line. The administrator would then call-in the device, log in with the password, and check the state of «consumer», turn it on or off, change password or some other settings. Current version has only one relay.




Phone Recorder





PIC based Caller ID

Caller Line Identification displays on a (2x16) LCD the phone number of the person who is ringing you, before you even answer, this number stays on the LCD till it will be replaced by a new received phone number or if the button is pressed.




PIC Phone Line Controller v2

This is a newer version of previous device with a single relay. This one can have up to 6 relays and 6 sensor-state inputs. The task was to build a device that connects to the phone line and has a relay as an output switch. It should also sense if the connected «consumer» is turned-on or off and report to the administrator at the other end of the phone line. The administrator would then call-in the device, log in with the password, and check the state of «consumer», turn it on or off, change password or some other settings.




Remote control using telephone

Here is a telephone remote 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.




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.




Telephone Amplifier

While talking to a distant sub- scriber 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. There is no extra power source needed to power up the circuit, as it draws power from the telephone line itself. The amplifier will provide fairly good volume for the telephone conversation to be properly heard in a living room. A volume control is included to adjust the volume as desired. The circuit is built around IC LM386.




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.




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 ‘MICIN’ socket of the tape recorder. Points X and Y in the circuit are connected to the telephone lines. Resistors R1 and R2 act as a voltage divider. The voltage appearing across R2 is fed to the ‘MIC-IN’ socket of the tape recorder. The values of R1 and R2 may be changed depending on the input impedance of the tape recorder’s ‘MIC-IN’ terminals. Capacitor C1 is used for blocking the flow of DC. The second part of the circuit controls relay RL1, which is used to switch on/off the tape recorder. A voltage of 48 volts appears across the telephone lines in on-hook condition. This voltage drops to about 9 volts when the handset is lifted. Diodes D1 through D4 constitute a bridge rectifier/polarity guard. This ensures that transistor T1 gets voltage of proper polarity, irrespective of the polarity of the telephone lines.




Telephone FM Transmitter

This FM transmitter attaches in series to one of your phone lines. When there is a signal on the line (that is, when you pick up the handset) the circuit will transmit the conversation. In particular it will radiate from the phone line itself. It is a passive device - there is no battery. It uses the signal on the phone line for power. No aerial is needed - it feeds back the RF signal into the phone line which radiates it in the FM band. The frequency of transmission may be adjusted by the trimcap.




Telephone In-Use Indicator

This is telephone in-use indicator that allows to record important telephone conversations.




Telephone Listening Bug

Here is a simple transmitter that when connected to a phone line, will transmit anything on that line (execpt the dial tone) to any FM radio. The frequency can be tuned from 88 to about 94Mhz and the range is about 200 feet. It is extremely easy to build and is therefore a good, useful beginner project.




Telephone Receiver

An interesting circuit and handy electronic telephone receiver, suited for receiving incoming calls, is described here. This circuit can be connected to almost all types of telephone exchange lines. To simplify the gadget, the dialer section has been omitted. The circuit can be constructed on a medium size veroboard.




Telephone Receiver

An interesting circuit for a me- dium performance handy electronic telephone receiver, suited for receiving incoming calls, is described here. This circuit can be connected to almost all types of telephone exchange lines. To simplify the gadget, the dialler section has been omitted. The circuit can be constructed on a medium size veroboard. Wiring and components layout are not very critical. For compactness, enclose the wired circuit in a plastic cabinet as shown in Fig.(a) here. In order to prevent undesired acoustic feedback, it is necessary to adjust the orientation of ear-piece (LS) and mouth-piece (MIC) at the final stage of construction. The circuit consists of four sections: ringer, voltage regulator, transmitter and receiver. The ringer section is built around capacitor C1, resistor R1 and electronic buzzer BZ1.




Telephone Recorder

This nifty little circuit lets you record your phone conversations automatically. The device connects to the phone line, your tape recorder's microphone input, and the recorder's remote control jack. It senses the voltage in the phone line and begins recording when the line drops to 5 volts or less. R1 1 270K 1/4 W Resistor R2 1.5K 1/4 W Resistor R3 68K 1/4 W Resistor R4 33K 1/4 W Resistor C1 0.22uF 150 Volt Capacitor Q1, Q2 2N4954 NPN Transistor D1 1N645 Diode MISC Wire, Plugs To Match Jacks On Recorder, Board, Phone Plug.




Telephone Recorder Switch

This circuit will allow you to record both sides of your telephone conversations for future reference. For commercial orders placed over the phone such a recording device is invaluable.




Telephone Remote Switch

This device connects to the telephone line and can be used to remotely control up to 4 relay outputs using a DTMF (tone dialing) telephone. A number of user settings are available to improve the useability and security of the device. The kit comes complete with a small plastic case with silk-screened front and rear panels.




Telephone Ringer by IC KA2411

Simple telephone Ringer with KA2411 IC.




Telephone Voice Changer

Although this kind of voice effect can be obtained by means of some audio computer programs, a few correspondents required a stand-alone device, featuring microphone input and line or loudspeaker outputs. This design fulfills these requirements by means of a variable gain microphone preamplifier built around IC1A, a variable steep Wien-bridge pass-band filter centered at about 1KHz provided by IC1B and an audio amplifier chip (IC2) driving the loudspeaker.




Watch-Dog for Telephones

Most of the telephone security devices available in market are simple but quite expensive. These devices provide blinking or beeping type line-tap/misuse indications. Quite often they do not offer guaranteed protection against unauthor-ised operation. A very simple and uni- que circuit of a telephone watch-dog to safeguard subscriber telephone lines against any fraud is described here. This little circuit keeps continuous watch over the telephone lines and sounds an alarm in case of any misuse. In addition it transmits a loud tone through the telephone lines to prevent further misuse.




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