Scale-Tronix 6702 - 4.40 AC Power Supplies and Rechargeable Batteries

display.
4.25.2 NON-VOLATILE MEMORY
The internal memory of microcomputer U10
does not retain data when the power is switched off.
Because some features of the scale may require
lasting data retention (such as last weight recall)
integrated circuit U is included. This device, called
an "electrically erasable programmable tead only
memory", or "EEPROM" will store selected
information for periods of up to 100 years.
Information needed to be stored to or retrieved from
U is sent in serial form using the lines SCL (serial
clock) and SDA (serial data). These are controlled by
microcomputer U10. A data bit (a high or low level)
is sent and received on SDA when the SCL. line
provides a pulse.
Resistors R54/R55 are provided as pull-ups on the
SCL/SDA lines to insure the data and clock pulses
are properly shaped. Capacitor C36 improves power
supply bypassing.
4.25.3 RESET GENERATION
In order for microcomputer 16 to properly
execute its software instructions it must be initialized
to the start of the program when power is first turned
on, Reset pin 9 of U10 will accomplish this when it
is set "high".
23005 R01 board: RC network C31/R40 is provided
to generate a momentary pulse on power up which is
coupled to the /RS pin of U10. No reset of port
expander integrated circuit U7 is provided. U7's reset
pin is permanently connected to ground through
resistor R39.
23005 ROZ board: A reset pulse of approximately
200 mS is automatically generated by “watchdog
timer” U11 when the Vcc level rises above 4.65 volts.
№ Усс is below 4,65 volts the reset line stays "high",
keeping the microcomputer U10 in an inactive state.
The reset puise is also connected to port expander
U7.
“The model 5102 also contains a jumper on J7 that
causes watchdog timer U11 to generate a reset pulse
to U10 in the event of a watchdog timeout due to
hardware or software failure.
4.30 DISPLAY BOARD
Presentation of the weight information is
performed by the model 22DSDP display board. it
incorporates LED (light-emitting diode) digits and
annunciators to provide a clear, bright, easy-to-read
display.
The weight value is displayed on six, 0.43” high
common cathode digits. These are driven in a
multiplexed fashion (one digit on at a time) by LED
driver UT. U1 receives the digit display information
from the microcomputer's parallel data bus (DB0-DB7)
and automatically performs the multiplexing function.
Resistor package RP1 sets the operating current level
for the displays.
A variety of LED annunciator lamps are contained on
the front panel to indicate "POUNDS" or
“KILOGRAMS”, "PRIOR WEIGHT", and "LO BATT".
These annunciator lamps contain multiple LED's to
provide an evenly illuminated surface. They are driven
by integrated circuit U2. U2 receives the on/off
information for the annunciators from microcomputer
U10 via port expander circuit U7. Resistor packs RP2
and RP3 provide current limiting for the annunciators.
Display boards 22DSP R01, 22DSP R02, and 22DSP
R03 are all equivalent in operation with some minor
changes in board layout to improve spacings. Seme
minor differences in connections to the terminals of the
resistor networks were also made to improve
spacings.
440 AC POWER SUPPLIES AND
RECHARGEABLE BATTERIES
Some versions of the SCALE-TRONIX® second
generation scales employ an AC power supply, or an
AC supply with rechargeable batteries. These are
described in more detail as follows:
4.40.1 MODEL 11801 POWER SUPPLY
This is a small power supply that is often used in
conjunction with a 6.0 volt, 450 Mill-amp hour nickel-
cadmium battery pack.
22 5002, 5102, 5602, 6002, 6102, 6202, 6502, 6702