Tone Dial Circuit; Circuit Description; Tone Frequencies - Panasonic EASA-PHONE KX-T2355 Service Manual And Technical Manual

m TONE DIAL CIRCUIT
Function:
The tone dialing circuit consists of a DTMF (Dual Tone Multi Frequency) signal generator (outputted from Pin 25 of the
microprocessor) for tone dialing, and also a circuit for outputting the signal to the line.
~The DTMF circuit identifies inputs from the 12 keys (1,2,3,4,5,6,7,8,9,0,xand #) by means of a total of seven frequencies,
that is four low frequencies (Low group) and three high frequencies (High group).
Circuit Description:
The signal flow to the line is as follows.
The DTMF signal is sent to the line via the following saith:
Q10 amplifies the DTMF signal.
Q3 is an amplifier which is used to output the signal to line.
Pin 25 of IC1—> R30, C18, C35— Q6 base—> Q6 emitter— C49— Handset Saeaken
The signal combination and frequency corresponding to each dial key is shown below.
Tone Frequencies
1209 Hz +
1.5%
770 Hz+ — 1336 Hz +
1.5% 1 'SY
852 Hz + 1477 Hz + +
1.5% 1.5%
4 9474 Hz +.
| 1.5%
cer,
: Horny