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Technical Supplement
9.6.11 Battery Voltage
9.6.12 Battery Type
9-28
The battery voltage circuit is illustrated in Figure 9-30.
Figure 9-30: Battery Voltage Circuit
The analog input voltage range of the CPU is 0-5 VDC. Because the battery
voltage may be as high as 6.2 V, R69 and R70 form a voltage divider to decrease
the measured battery voltage to a usable level. The gain is 0.75; thus, if the
battery voltage was 6 V, then the voltage of BAT_VOLT would be 6 × 0.75
which equals 4.5 V.
The software has the ability to determine when battery power is too low. If the
software determines that the battery voltage is too low to provide accurate
information, the software generates an audible signal and automatically switches
the unit off. The battery voltage data are also used to compensate for battery
voltage changes that can affect printout quality.
The battery type circuit is illustrated in Figure 9-31.
TP2
R100
VRECHARGE
15K
TEST
N-20
AUX
PCB
Figure 9-31: Battery Type Circuit
The unit operates on disposable batteries. Battery type input is digital; a high
input informs the CPU that rechargeable batteries are in use. If rechargeable
batteries are used, the battery and the VRECHARGE terminals are mechanically
connected. This applies the battery voltage to VRECHARGE, pulling
BAT_TYPE high. R100 and CR27 are a current-limiting resistor and a
voltage-clamping diode that are used to protect the input port from excessive
battery voltage. If disposable batteries are used, VRECHARGE is electrically
isolated, which allows R101 to pull BAT_TYPE input low.
VBAT
R69
15.8K
BATTERY
1%
BAT_VOLT
VOLTAGE
SENSE
R70
47.5K
1%
VCC
CR27
1N914
R101
150K
TP73
C62
.01UF
BAT_TYPE
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