Kenwood TK-2180 Service Manual page 11

6-2. Low battery warning
The battery voltage is monitored by the microprocessor
(IC502 pin 126 : BATTLVL). When the battery voltage falls
below the voltage set by the Low Battery Warning adjust-
ment during the transmission, the red LED blinks to notify the
operator that it is time to replace the battery (When the "On
TX" option (default setting) under the Battery Warning / sta-
tus function in the FPU is selected.). If the battery voltage
falls below 5.8V, the transceiver does not transmit and the
warning tone beeps while the PTT switch is pressed.
Low battery warning
The red LED blinks during
the transmission.
The red LED blinks and
the warning tone beeps while
the PTT switch is pressed.
6-3. Battery type detection
The transceiver automatically detects the battery type,
measuring the resistance between the S-terminal and GND
terminal on the battery pack and changes the supplied volt-
age to the S-terminal as below. The microprocessor then de-
tects the battery type.
Resistor value Battery type
Open Ni-Cd
150kΩ Ni-MH
47kΩ Li-ion
Short Battery case
6-4. Key input
When any key is pressed, KI1 or KI2 become Low. And
CPU (IC502) set Q1 to Q9 "Low" sequentially. The CPU de-
tects which key is pressed, according to the voltage of KI1
and Kl2 and Q1 to Q9 timing.
7. Signaling Circuit
7-1. Encode
■ Low-speed data (QT, DQT)
Low-speed data is output from pin 33 of the CPU. The
signal passes through a low-pass filter (IC601 1/2), and goes
to the summing amplifier (IC600 2/2). The signal is mixed
with the audio signal and goes to the VCO and TCXO (X1)
modulation input after passing through the D/A converter
(IC605) for BAL adjustment.
CIRCUIT DESCRIPTION
Battery condition
The battery voltage is low but
the transceiver is still usable.
The battery voltage is low and
the transceiver is not usable
to make calls.
Input voltage of S-terminal
4.5~5.0V
2.0~3.34V
0.8~2.0V
0~0.8V
7
HSDO
IC502
CPU
33
LSDO
■ High-speed data (5-tone, DTMF)
High-speed data (HSD) is output from pin 7 of the CPU.
The signal passes through a low-pass CR filter and provides a
TX HSD tone and a RX HSD tone. TX HSD deviation making
an adjustment by microprocessor is passed through the
switch (IC606) and then applied to the audio processor
(IC607).
The signal is mixed with the audio signal and goes to the
VCO and TCXO. The RX HSD tone is passed a summing am-
plifier (IC607). The D/A converter (IC605) for audio control,
audio power amplifier and then to the speaker.
■ MSK
MSK signal is output from pin 6 of IC607. The signal
passes through the D/A converter (IC605) for the MSK devia-
tion adjustment, and is routed to the VCO. When encoding
MSK, the microphone input signal is muted.
4 1
5 2
6 3
9 #
8 0
7 *
C S
S1 A
S2 B
Fig. 11 Key input
IC607
AQUA-L
IC606
EXTLIMIN MOD
SW
6
5
SW
RX Audio
SW
SUM
RXAF
LPF
IC601
(1/2)
Fig. 12 Encode
TK-2180
CK
KI1
DT
KI2
SPSTB
IC502
CPU
IC500
Q1 Vdd
Q2 LCK
Q3 DATA
Q4 CLK
Q5 Vss
Q6 SO
Q7 Q10
Vss Q9
Q8
IC602 (1/2)
BUFF
TCXO
AMP
IC605
O1 I1
IC600 (2/2)
SUM VCO
I2 O2
O6
I6
AF AMP
11