wave.
The signal flow to the line is as follows.
Pin 25 of IC1
Q3
R9
Q1
Tel Line.
The DTMF signal is sent to the line via the following path. Q3 is an amplifier which is used to
output the signal to line.
Shown below is the signal flow used to output the DTMF signal from the handset as a monitor
tone when a dial key is pressed.
Pin 3 of IC1
R24
C15
Handset Speaker.
The signal combination and frequency corresponding to each dial key is shown on next page.
12.3. Ringer Circuit
11
