The doorbell sound circuit was two-tone sound. With the switch S1. working of the circuit, IC1 is a frequency division circuit, and a sound frequency generator came out.by C1, R1 is the frequency generator.
This audio signal from pin 7 and pin 4 to pin 1 and pin 8 of the IC2a, IC2c respectively. The IC2b of a frequency converter to control IC2c.When control signal during the low (Low) 1.25 kHz frequency coincides with IC2a.At same time, the control signal is in a high state IC2b (high) , 300 Hz frequency IC2c parties. Output on pin 3 of low IC2a under the same conditions, production and IC2c IC2a IC2d.Which is sent to act as a signal and the output transistors act as switches Q1 and tones amplifiers.The can be heard as two strokes. R3 acts as a volume, add more value to make the softest sound, but softer, a source of 6 volts.
This audio signal from pin 7 and pin 4 to pin 1 and pin 8 of the IC2a, IC2c respectively. The IC2b of a frequency converter to control IC2c.When control signal during the low (Low) 1.25 kHz frequency coincides with IC2a.At same time, the control signal is in a high state IC2b (high) , 300 Hz frequency IC2c parties. Output on pin 3 of low IC2a under the same conditions, production and IC2c IC2a IC2d.Which is sent to act as a signal and the output transistors act as switches Q1 and tones amplifiers.The can be heard as two strokes. R3 acts as a volume, add more value to make the softest sound, but softer, a source of 6 volts.
