Telephone Ringer


Posted on Feb 7, 2014

This circuit generates the sound of the electronic ringer found in modern telephones, supplanting the 2-bell electromechanical ringers used previously. The ringing pattern follows the United States convention of 2 seconds on, and 4 seconds off. During the `on` interval, the tone alternates between two selectable frequencies at a rate of 20Hz. Refe


Telephone Ringer
Click here to download the full size of the above Circuit.

ring to the schematic, NAND Schmitt trigger U1A is configured as a relaxation oscillator, adjusted with RV1 for a 40Hz waveform at test point TP1. This waveform is divided by flip-flop U2A to provide a 20 Hz, 50-percent duty cycle square wave at U2A`s Q output, and a complimentary square wave at U2A`s Q-not output. When U2A`s Q output is high, the relaxation oscillator formed by U1B is enabled. When U2A`s Q-not output is high, the relaxation oscillator formed by U1C is enabled. NAND gate U1D provides an OR function for the two oscillator outputs, and drives flip-flop U2B, which divides the waveform by two to ensure a 50 per-cent duty cycle. The resulting waveform at U2B`s Q output is a square-wave that alternates between two audible frequencies at a 20Hz rate. The pitch of these frequencies are individually adjustable from approximately 500Hz to 2500Hz with RV2 and RV3, and may be selected for a suitable sound output. A frequency divider chain consisting of U4, U5 and U6 is driven from the 20Hz waveform at U2A`s Q-not output. U4 and U5 provide a frequency division of 40, resulting in a 0. 5Hz square wave at U5B pin 13. This square wave drives U6, which is configured as a divide-by-3. U6`s "0" output is a 0. 167Hz waveform which is at a high state for 2 seconds, and a low state for 4 seconds. Paralleled gates U3A and D, driven by U2B`s Q output, drive one side of the piezo audible transducer, as well as the inputs of two...




Leave Comment

characters left:

Related Circuits

  • New Circuits

    .

     


    Popular Circuits

    Aquarium Auto Controller using PIC18F4520
    Phone Message Flasher
    Digital tachometer using 8051
    IP phone to analog phone or modem audio interface circuit
    Fan Controller Using Just Two Components
    Low Cost 1000 Watt 300 Volt Rf Power Amplifier For 27.12mhz
    7.2V Battery Replacement Power Supply For Camcorders
    Simple RS232 Serial Interface Circuit
    Electronic pulse circuitry fishing



    Top