12.3. Ringer Circuit
Circuit Operation:
The bell signal passes through C1 (R1) supplying power to pin 1 of IC2.
The ring signal is output from Pin 5 of IC2, and its volume is adjusted in 3 steps (H-L-OFF) by
SW3 then impressed on the ceramic sound generator, and so is generated.
Output frequency is controlled by R2 and C3 following below formula.
12.4. Power Circuit and Redial Back-up Circuit
Function:
This set is powered from the line. When it is an OFF-HOOK status, Tel Line D1 Q1 R14
pin 17 of IC1 (to become the power supply for IC1 speech network).
The voltage from the line is turned into a constant voltage by D6 and then supplied to the IC1 and
sending and receiving circuit of the set.
At ON-HOOK status the voltage from the line via R40, R5 is turned into a constant voltage by D8,
and then become power supply for IC1 (Pin17), and the redial Back-up will be done.
12.5. Sending Circuit (Tx)
When a person talk through the Handset, the voice analog signal flow from the
mic C20 R33 Q9 R38 C23 Q3 Q1 D1 Tel line.
* Q9 and Q3 is an amplifier for the voice signal.
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