DTMF Circuits

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 number is decoded by DTMF decoder CM8870P1 (IC1), which converts the received DTMF signal into its equivalent BCD number that corresponds to the dialled number. This binary number is stored sequentially in 10 latches each time a number is dialled from the phone. The first number is stored in IC5A (1/2 of CD4508) while the second number is stored in IC5B and so on...

Remote Control using DTMF

Here is a circuit of a remote control unit which makes use of the radio frequency signals to control various electrical appliances. This remote control unit has 4 channels which can be easily extended to 12. 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 transmit the control signals and hence it can be used for control from almost anywhere in the house. Here we make use of DTMF (dual-tone multi frequency) signals (used in telephones to dial the digits) as the control codes. The DTMF tones are used for frequency modulation of the carrier...

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 telephone key-pad). The DTMF signals on telephone instrument are used as control signals. The digit 0 in DTMF mode is used to toggle between the appliance mode and normal telephone operation mode. Thus the telephone can be used to switch on or switch off the appliances also while being used for normal conversation...

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...

DTMF decoder with voice!

The Talking Phone Dial Monitor detects the tones generated when numbers are dialed on your touch tone telephone and speaks the numbers that were dialed. This verifies that you dialed the correct number and is especially useful when the keypad is not well lighted or if the person dialing cannot see the keypad well for any reason. The numbers that are spoken can be prerecorded by speaking into a built-in microphone and can be re-recorded at any time if desired...

DTMF FM PLL Receiver

This project is a PLL synthesized FM radio which can decode DTMF. The receiving frequency can be set by the PLL circuit from 80-140MHz. The receiver is VERY stable, high sensitivity and easy to build and tune. The FM receiver can decode DTFM signals from a transmitter and present the DTMF data on three LED display. The complete background about this project can be found at my "Wife replace" project. This part is a FM receiver based on a PLL synthesizer UMA1015. The frequency of the PLL synthesizer is programmed by a PIC processor which also control the DTMF circuit and the LED to display information. The Audio output from the FM receiver is connected to a DTMF circuit which is specialised to identify and decode DTMF signals. If there is a valid DTMF tone the PIC will read the data and present it on the LED display. Since I have 3 LED I can display 000 to 999 on the display. ..

DTMF Phone Dialer with PIC16F690 and NTE1690

The circuit uses a NTE1690 DTMF dialer chip and a PIC16F690 microcontroller. Because this is an IP phone and I cannot just send the DTMF tones over the line, the easiest place to plug in the box is between the phone and the handset. The box has two RJ9 ports at the back - one gets connected to the headset's port on the phone, the other to the headset itself. The dial tones are sent over the microphone line. This way, it works both on IP-phones, and on standard (old fashioned, non-IP) ones...

Telephone Intercom - DTMF

This version of the Link uses DTMF tones for dialling both internally between handsets, and externally for outside calls. Remember, in some countries, it is ILLEGAL to simply connect unapproved and untested equipment to Telco lines, so avoid the fine and confiscation of your equipment, and ask nicely? OK ? now, the link A2B as shown has only 2 handsets, numbered ?1? and ?2?. When the Link is at reset, both phones are ?on hook? and no external incoming call is present. If an outside call rings the electronic bell ringer (EBR - not shown, but connected across L1 and L2) then anyone near either of the two phones can answer that call by simply picking up a handset (?off hook?) and dialling a zero (0) This provides a ?set? pulse for FF2 and operates the OSL relay, and places BOTH handsets across the outside Telco line...

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...

The circuit described here can be used to switch up to nine appliances (corresponding to the digits 1 through 9 of the telephone key-pad). The DTMF signals on telephone instrument are used as control signals. The digit 0 in DTMF mode is used to toggle between the appliance mode and normal telephone operation mode. Thus the telephone can be used to switch on or switch off the appliances also while being used for normal conversation...

Heres 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. The MT8870 is an 18-pin IC. It is used in telephones and a variety of other applications...

This remote control unit has 4 channels which can be easily extended to 12. 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...

The circuit presented here enables you to detect any object capable of reflecting the IR beam and moving in front of the IR LED photodetector pair up to a distance of about 12 cm from it. The circuit uses the commonly available telephony ICs such as dial-tone generator 91214B/91215B (IC1) and DTMF decoder CM8870 (IC2) in conjunction with infrared LED (IR LED1), photodiode D1,..

Our DTMF decoder can be powered from a 9V battery or from your parallel printer port. It can detect and display all 16 DTMF digits on your computer screen in real-time. The Window`s program can be placed in the minimize mode and still detect tones while you use your computer to do other things like Net surfing!!!!..

The DTMF (Dual Tone Multiple Frequency) application is associated with digital telephony, and provides two selected output frequencies (one high band, one low band) for a duration of 100 ms. A benchmark subroutine has been written for the COP820C/840C microcontrollers, and is outlined in detail in this application note...