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KX-T2388
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Circuit Diagram (for Cradle)
TEL LINE JACK
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Mi TONE
DIAL CIRCUIT
Functlon:
The tone dial circuit consists of a DTMF (Dual Tone Multi Frequency) signal generator (outputted from pin 13 of
the microcessor) for tone dialing, and also a circuit for outputting the signal to line.
The DTMF circuit identifies inputs from 12 keys (1, 2, 3, 4, 5, 6, 7, 8, 9, 0, X and #) by means of a total of seven
frequencies, that is four low frequencies (Low group) and three high frequencies (High group).
Circuit
Operation:
When a dial key is presses, a DTMF signal is outputted from pin 16 of IC1 as an analog synthetic wave.
The signal flow to the line is as follows.
Pin 13 of IC1 > R16
C11
> R38 > pin 12 of IC2 — pin 4 and 5 of IC2.
The DTMF signal is sent to the line via the following path.
IC2 is an amplifies the DTMF signal.
is an amplifier which is used to output the signal to line.
The 1 KHz confirmation tone is heard from the speaker of the handset.
Pin 16 of IC1 -» R18 -Ci2
pin 14 of IC2 — pin 4 of IC2 — Telephone Line.
The signal combination and frequency corresponding to each dial key is shown below.
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