Phone Ringer Circuit
Created: Nov 06, 2014
No description available.
Modern telephone nowadays has the same concept of a ringer circuit later before electronics has been integrated to it. Its major development is the electronic ringing chip and small speaker replacing the coil-controlled bell. The capacitor is still used in series with ring IC input to make only AC pass to the ring chip. The electronic ringing circuits are not sensitive to the ringing voltage and they easily ring with ring signal frequencies between 16 Hz and 60 Hz.
The 74HC4060 is a high-speed Si-gate CMOS device and is pin compatible with the HEF4060. It has a 14-stage ripple-carry counter/dividers and oscillators with three oscillator terminals (RS, RTC and CTC), ten buffered outputs (Q3 to Q9 and Q11 to Q13) and an overriding asynchronous master reset (MR). The oscillator configuration allows design of either RC or crystal oscillator circuits. The oscillator may be replaced by an external clock signal at input RS. In this case keep the other oscillator pins (RTC and CTC) floating. The counter advances on the negative-going transition of RS. A HIGH level on MR resets the counter (Q3 to Q9 and Q11 to Q13 = LOW), independent of other input conditions. In the HCT version, the MR input is TTL compatible, but the RS input has CMOS input switching levels and can be driven by a TTL output by using a pull-up resistor to VCC.
This circuit shows how a very complex set of pulses can be produced via a very simple circuit. The CD4060B IC produces three kinds of pulses. Preset RV1 is fine-tuned to get 0.3125Hz pulses at Q13 of IC1. At the same time, pulses obtainable from Q11 will be of 1.25 Hz and 20 Hz at Q7. The three output pins of IC1 are connected to base terminals of transistors QT1, QT2, and QT3 through resistors R1, R2, and R3, respectively. Working with a built-in oscillator-type piezo-buzzer generates about 1kHz tone. In this particular circuit, the piezo-buzzer is turned 'on' and 'off' at 20 Hz for ring tone sound by transistor QT3. 20Hz pulses are obtainable at the collector of transistor QT3 for 0.4-second duration. Just after a time interval of 0.4 second, 20Hz pulses become again obtainable for another 0.4-second duration. This is followed by two seconds of no sound interval. Thereafter the pulse pattern repeats by itself.