Signalling circuit, Circuit description, 2. low battery warning – Kenwood TK-480 User Manual

Page 19: 3. key input, 1. encode • low-speed data (qt,dqt,ltr), High-speed data (dtmf), Fig. 12 encode

TK-480/481

CIRCUIT DESCRIPTION

6-2. Low battery warning

The battery voltage is monitored by the microprocessor

(IC15). When the battery voltage falls below the voltage set
by the Low Battery Warning adjustment, the red LED
flashes to notify the operator that it is time to replace the
battery. If the battery voltage falls even more (approx. 5.8V),
a beep sounds and transmission is stopped.

Low battery warning

Battery condition

The red LED flashes during

The battery voltage is low but

transmission

the transceiver is still usable.

The red LED flashes and

The battery voltage is low and

continuous beep sounds

the transceiver is not usable to

while PTT pressed

make calls.

6-3. Key input

If the clock is supplied to CLK terminal when the RES

terminal (CPU pin 53) of the decade counter (IC301) is set to
Low, Q0 to Q7 become High sequentially. Normally, KI1 and
KI2 are Low (pulled down). When any key is pressed, KI1 or
KI2 become High. The CPU detects which key is pressed,
according to the voltage of KI1 and KI2 and clock timing.

Fig. 10

Key input

Fig. 11

Decade counter timing chart

7. Signalling Circuit

7-1. Encode
• Low-speed data (QT,DQT,LTR)

Low-speed data is output from pin 36 of the CPU. The

signal passes through a low-pass CR filter, and goes to the
summing amplifier (IC3 1/2). The signal is mixed with the
audio signal and goes to the VCO (IC14) and VCXO (X2)
modulation input after passing through the D/A converter
(IC4) for BAL adjustment.

• High-speed data (DTMF)

High-speed data is output from pin 35 of the CPU. The

signal passes through a low-pass filter consisting of IC23,
and provides a TX DTMF tone and a RX DTMF tone including
a beep tone. The TX DTMF tone is passed to the D/A con-
vertor (IC4) for DTMF deviation adjustment, and then ap-
plied to the audio processor (IC12).

The signal is mixed with the audio signal and goes to the

VCO and VCXO. The RX DTMF tone is passed a summing
amplifier (IC3 2/2), the D/A convertor (IC4) for audio control,
audio power amplifier and then to the speaker.

• MSK

MSK signal is output from pin 6 of IC12. The signal

passes through the D/A converter (IC4) for the MSK devia-
tion adjustment, and is routed to the VCO. When encoding
MSK, the microphone input signal is muted.

Fig. 12

Encode

KI2

Vss

Vdd

RES

CLK

KRST

IC301

KI1

IC15
CPU

16 keys

RESET

CLOCK

INHIBIT

CARRY

OUT

BUFF

AMP

VCXO

IC1

MUTE

VCO

IC14

Q21

LPF

HSD
OUT

IC23

R111

R107

C141

C138

R148

LSD

OUT

IC15
CPU

IC4

D/A (ADJ)

SUM

MIC IN

SUM

IC3 (1/2)

IC12

AF AMP

SUM

IC3 (2/2)

RX audio