User Guide

After Sales
Technical Documentation
Handsfree Desktop Charger CHH–7
Original, 11/94Page 22
Spare battery voltage and V voltage are determined by reading the
VBAT line state. Voltages are measured through resistor divider R250 /
R251 and the amplifier N250–B.
Spare battery size is determined by reading the BSI line state. This is
pulled to the +5V reference voltage by R243. In the battery pack a ’size’
resistor is connected between BSI and GND.
Temperature is measured over the BTEMP line. This line is pulled to the
+5V reference voltage by R242. In the battery pack an NTC resistor is
connected between BTEMP and GND.
Spare Battery Discharging
The HF desktop charger is also provided with a discharge function. This
is activated by pressing the discharge button S300. Resistors R230 to
R237 determine the discharge current which is fed through switching
transistor V230 which is controlled by the processor. Discharging is
indicated by a flashing red LED (V331). The battery is discharged to +5V
and thereafter charged normally to full capacity.
Microphone Amplifier and Corresponding Switches
Transistor amplifier circuit V420 and the corresponding resistors and
capacitors supply bias current for the microphone. Operational amplifier
N430–B amplifies the microphone signal before it is fed to the phone. The
gain of the op amp is approximately 38 dB.
The HF microphone signal is fed to the phone via analogue switches
D400–B and D400–C. The microphone signal XMIC, from the data
accessory (X510) is fed to the phone via switches D400–A and D400–C.
The supply voltage for the amplifier and the analogue switches is taken
from the +5VAN regulator N102. The +VAREF reference voltage is
derived from the N430–A and the +5VAN analogue voltage.
Speaker Amplifier and Corresponding Switches
The XEAR signal from the phone is fed to the HF speaker via analogue
switches D410–C and D410–B. The XEAR signal is amplified about 23dB
(+39dB via amplifier N460, –1dB via the analogue switches, and –15dB
via resistors R460 and R461). The XEAR signal from the phone can be
fed to data accessory (X510) via analogue switches D410–C and D410–A.
The supply voltage +10VAS for the speaker amplifier is derived from the
regulator N100.
Circuit Description (DC4H)
The DC4H–module electronics comprise noise reduction components
only. ’Spark gaps’ E1, E2, E4 and E8 protect against electrostatic
discharge. Refer to Figure 6 – Circuit Diagram (sheet 3).