Adam Equipment QBW Series User manual

Adam Equipment
QBW Scale
SERVICE MANUAL
ADAM EQUIPMENT CO. LTD.
p.n. 6064, Rev. A, June 2005
@Adam Equipment Company 2004

@Adam Equipment Company 2004

CONTENTS
INTRODUCTION.................................................................................................................2
SPECIFICATIONS...............................................................................................................2
SCALE RANGES AND RESOLUTIONS..............................................................................2
TROUBLE SHOOTING GUIDE ...........................................................................................4
DISPLAY AND KEYS...........................................................................................................5
POWER...............................................................................................................................5
ZERO / TARE......................................................................................................................6
WEIGHING UNITS SELECTION.........................................................................................7
CALIBRATION.....................................................................................................................7
USER SETUP PARAMETERS ............................................................................................8
FUNCTION OF THE KEYS..............................................................................................8
BUZZER ON/OFF ............................................................................................................9
AUTO SWITCH-OFF TIME..............................................................................................9
ENABLED UNITS...........................................................................................................10
VIEWING ADC COUNTS...................................................................................................10
LOADING DEFAULTS.......................................................................................................10
ERRORS ...........................................................................................................................11
QBW HARDWARE OVERVIEW........................................................................................12
QBW ASSEMBLY..............................................................................................................16
LOAD CELL ASSEMBLY...................................................................................................19

@Adam Equipment Company 2004
2
INTRODUCTION
•The QBW series of scales are simple, easy to use scales with an internal
rechargeable battery.
•The weighing process is fast and accurate, making it suitable for general purpose
weighing applications.
•There are 5 models in this series with capacities ranging from 1.5 kilograms to 30
kilograms.
•All have stainless steel weighing platforms on an ABS plastic base assembly.
•Keypads are sealed, with colour coded membrane switches.
•The displays are large, easy to read liquid crystal type displays (LCD).
•The LCD normally shows the weight and the previously-selected units of the weight
(Grams, Kilograms, Ounces, Pounds or Pounds & Ounces).
SPECIFICATIONS
Operating temperature 0ºC TO 40ºC
32ºF TO 104ºF
Battery Internal Rechargeable Battery
(approx. 150 hours Operation)
Power Supply Adapter 9 VAC, 500mA
Applications General Purpose Weighing Scale
Stabilisation Time 2 seconds typical
Calibration Manual External
Display 4 and 1/2 Digits LCD Display
Balance Housing ABS Plastic, Stainless Steel Platform
Pan Size 225 X 275 mm (8.9” X 10.8”)
Dimensions ( W X D X H) 315 x 355 x 110 mm (12.4”X14”X4.3”)
Gross weight Approx. 4.0 Kg (8.8 lb.)
SCALE RANGES AND RESOLUTIONS
5 different ranges and resolutions are available for the scale, depending on the weighing
range of the load cell fitted and its associated software.
The ranges and resolutions for each capacity in all the available units are shown in the
following tables:

@Adam Equipment Company 2004
3
N
SCALE RANGE = 1.5 kilograms
SELECTED
UNITS FULL SCALE DISPLAY RESOLUTIO DISPLAY
Grams 1500.0 g
1500,0g 0.5 g 0,5g
Kilograms 1.500 kg 1,500kg 0.001 kg 0,001kg
Ounces 52.90 oz
52,90oz 0.02 oz 0,02oz
Pounds 3.306 lb
3,306lb 0.002 lb 0,002lb
Pounds & Ounces 1 lb15.9 oz* 1_15,9lb-oz 0.1 oz _0,1lb-oz
SCALE RANGE = 3 kilograms
SELECTED
UNITS FULL SCALE DISPLAY RESOLUTIO
N DISPLAY
Grams 3000 g
3000g 1 g 1g
Kilograms 3.000 kg
3,000kg 0.001 kg 0,001kg
Ounces 105.80 oz
105,80oz 0.05 oz 0,05oz
Pounds 6.615 lb
6,615lb 0.005 lb 0,005lb
Pounds & Ounces 6 lb 10 oz 6_10lb-oz 1 oz 0_1lb-oz
SCALE RANGE = 6 kilograms
SELECTED
UNITS FULL SCALE DISPLAY RESOLUTIO
N DISPLAY
Grams 6000 g
6000g 2 g 2g
Kilograms 6.000 kg
6,000kg 0.002 kg 0,002kg
Ounces 211.6 oz
211,6oz 0.1 oz 0,1oz
Pounds 13.23 lb
13,23lb 0.01 lb 0,01lb
Pounds & Ounces 13 lb 4 oz 13_4lb-oz 1 oz 0_1lb-oz
SCALE RANGE = 15 kilograms
SELECTED
UNITS FULL SCALE DISPLAY RESOLUTIO
N DISPLAY
Grams 15000 g
15000g 5 g 5g
Kilograms 15.000 kg
15,000kg 0.005 kg 0,005kg
Ounces 529.0 oz
529,0oz 0.2 oz 0,2oz
Pounds 33.06 lb
33,06lb 0.02 lb 0,02lb
Pounds & Ounces 19 lb 15 oz* 19_15lb-oz 1 oz 0_1lb-oz
SCALE RANGE = 30 kilograms
SELECTED
UNITS FULL SCALE DISPLAY RESOLUTIO
N DISPLAY
Grams 19999 g*
19999g 10 g 10g
Kilograms 30.00 kg
30,00kg 0.01 kg 0,01kg
Ounces 1058.0 oz
1058,0oz 0.5 oz 0,5oz
Pounds 66.15 lb
66,15lb 0.05 lb 0,05lb
Pounds & Ounces 19 lb 15 oz* 19_15lb-oz 1 oz 0_1lb-oz
*NOTE: Ranges marked with an asterisk are limited by the range of displayable numbers, not by the
maximum capacity of the scale, and will show an “
E Or ” message when the result is over range, rather
than an “
EOL ”message when the scale is overloaded.

@Adam Equipment Company 2004
4
TROUBLE SHOOTING GUIDE
SYMPTOM POSSIBLE CAUSE SUGGESTIONS
Blank display when the [On]
key is pressed without the
charger being connected.
Battery discharged.
Battery disconnected.
Plug in mains power supply
/charger.
Check battery connections.
Blank display when [On] is
pressed with charger
connected.
Internal power cable is
disconnected.
Keypad cable is
disconnected.
Reconnect cable from power
supply board to the main
board.
Reconnect cable from
keypad to the main board.
Display shows “ EHi ” at
power up. Load present on weight
pan. Switch off instrument. Remove load from weight
pan. Switch on again.
Display shows “ ELo ” at
power up. Weighing pan not fitted.
Load cell disconnected. Switch off instrument. Fit
plastic and metal weight
pan. Switch on again.
Check connections between
load cell and the main board.
Weighing readings are
incorrect. Scale requires re- calibration. Recalibrate using external reference mass.
Weighing readings are
unstable. Draught or vibration. Ensure scale is placed on a firm, vibration-free surface
away from sources of
draught.
Display shows “ EOL ” during
weighing. Weighing pan is
overloaded. Remove weight from pan.
Display shows “ EOr ” during
weighing. Weight value is too large
to be displayed in
currently-selected units.
Remove weight from pan or
select alternative units.
Charge LED does not
illuminate when charger
plugged in.
No mains supply to the
charger. Check the wall socket.
Charge LED shows green
but scale does not function
without charger connected.
Battery faulty or
disconnected.
Internal fuse on power
supply board blown.
Check battery connections.
If connections OK, replace
battery.
Replace fuse with one of the
same rating.
Charge LED remains red
after several hours of
charging.
Battery faulty. Replace battery.

DISPLAY AND KEYS
POWER
The scale is turned on by pressing the [On] key. There should be no load on the scale
when power is applied.
When the scale first powers up, the display will show the software revision number in the
form “
rX.XX ”. After about 2 seconds the display will then show the rated scale capacity.
This will be in the form “
CXXkg ”, where XX is the capacity in kilograms if the last selected
units were Grams or Kilograms, or “
C XX lb ”, where XX is the capacity in pounds if the last
selected units were Pounds, Ounces or Pounds & Ounces. After a further 2 seconds all
the display segments will turn on for approximately 2 seconds. The scale is then zeroed
and displays a zero reading, accompanied by the last selected units.
If the reading from the scale indicates that a load is in place on the scale at power-up, an
error message “
E Hi ”will flash on the display for about 5 seconds. If the reading from the
scale indicates that the weighing pan is not in place on the scale at power-up, an error
message “
E Lo ”will flash on the display for about 5 seconds. The scale will then operate,
but will not have established a new no-load value. In order to achieve this, the scale
should be powered down, the load removed or the weighing pan fitted, and the scale
powered up again.
The scale is turned off by pressing the [Off] key or by the timed automatic power-off
function (if enabled). A voltage detector is also included, which is used to indicate a low
battery condition by displaying the battery symbol. If the scale is not then attached to a
charger or manually switched off, the electronics will subsequently shut down the scale,
even if the automatic power-off is disabled.
@Adam Equipment Company 2004
5

ZERO / TARE
A zero or tare operation may be performed at any time by pressing and then releasing the
[Zero/Tare] key. The display will show “- - - -” until the key is released, followed by the
message “
tArE ”during tare value measurement, then the displayed weight value will be
set to zero.
If the tare reading is within a small range of the initial no-load value established at switch
on, the zero indicator will be displayed and the scale will still have the maximum capacity
available for weighing before an overload condition is displayed.
If however the tare reading is greater than this small range, indicating that a weight is
present, the scale will tare. The weight value will still be displayed as zero, but will show
the tare indicator instead of the zero indicator and the additional capacity before an
overload condition is displayed will be reduced by the amount of weight on the scale when
it was last tared.
If the scale is unable to obtain a stable weight value during the taring process after a
number of retries, it will display an error message “
E St ”, then abort the tare attempt and
return to weighing.
Whenever the scale is subsequently displaying a zero value, either the zero or the tare
indicator will be displayed.
Tare
Stable
Zero
Low Bat
Whenever a weight is put on to the scale the zero, tare and stable symbols will all turn off,
then when the reading has stabilised, the stable symbol will turn on. The units symbol will
be on at all times during normal weighing.
@Adam Equipment Company 2004
6

@Adam Equipment Company 2004
7
WEIGHING UNITS SELECTION
The desired weighing units may be selected by pressing the [Units] key (display shows “--
- -”) and then releasing it. The display will select each of the available units of weight in
turn, indicating the currently-selected units and the current weight value in the new units.
The units available for selection are set in the user set-up function as described below.
NOTE: If there is sufficient weight on the scale to cause the display to go out of range
when an alternative unit is selected, an “
E Or ” error message will be displayed. If this
occurs, the load should be removed, or the [Units] key should be pressed and then
released to select the next alternative unit.
CALIBRATION
It is only possible to perform a calibration of the scale using a single value of standard
mass which is equal, or near to, the maximum capacity of the scale. If metric units (i.e.
Grams or Kilograms) are selected, the value of the calibration mass required is the
maximum capacity of the scale in Kilograms. If imperial units (i.e. Pounds, Ounces or
Pounds & Ounces) are selected, the value of the calibration mass required is in Pounds as
shown in the following table:
Maximum Scale Capacity
(kg) Calibration Mass (lb)
1.5 3
3 5
6 10
15 30
30 60
The software includes checks to prevent the calibration from being performed if there is no
weight or a grossly incorrect weight on the scale, or it is overloaded.
Procedure:
•Press and hold the [Cal] key. The display shows “-- - -”. After 3 seconds the display
will change to “
C 0 ”. Release the key. If the [Cal] key is released within 3 seconds,
the calibration request will be ignored and the scale will return to normal weighing.
•Ensure that there is no weight on the balance, and then press the [Cal] key again.
The display will show “
tArE ”. Release the key.
•If the no-load calibration value is acceptable, the display will then show “ C XX uu ”
where
XX is the value of calibration mass required, and uu is the units (lb or kg) for
the calibration mass, e.g. “
C 6 kg ”for a 6 kilogram mass, or “ C 10 lb ” for a 10
pound mass.

@Adam Equipment Company 2004
8
•Place the correct calibration mass on the scale.
•Press the [Cal] key again. The display will show “
CAL ”. Release the key. The
display will continue to show “
CAL ” until calibration is complete and then return to
normal weighing, when it should display the correct calibration weight value in the
currently-selected units.
NOTE: If the no-load or full-load reading is too low, an “
ELo ”error will be displayed.
If the no-load or full-load reading is too high, an “ EHi ”error will be displayed.
If the no-load or full-load reading is unstable, an “ ESt ”error will be displayed.
If any of these conditions occur, or if [Cal] is not pressed within 10 seconds of the
“
C 0 ”message being displayed, the calibration procedure will be aborted and the
scale will return to normal weighing using the previous tare and calibration values.
USER SETUP PARAMETERS
FUNCTION OF THE KEYS
To enter the user-parameter setup menu, the [Zero/Tare] key should be held pressed, and
while the display is showing “----” the [Units] key should be pressed. The first setup option
will then be shown.
Release both the keys. If [Zero/Tare] is released without the [Units] key being pressed,
the display will change to “
tArE ”, a normal tare operation will be performed, and the setup
menu will not be entered.
When in the setup menu, the functions of the keys are as follows:
Press [Zero/Tare] to select alternatives within any parameter.
Press the [Cal] key (display shows “-- --”) then release the key to save any changes to the
current parameter, exit the setup menu, and return to normal weighing mode.
Press the [Units] key to save any changes to the current parameter and move to the next
setup parameter.

BUZZER ON/OFF
•The first option is to enable or disable the buzzer. The default state for this
parameter is buzzer on.
•The display will show “
buX ”, where X = 0 for buzzer off, X = 1 for buzzer on.
•Press the [Zero/Tare] key to change the enabled state of the buzzer.
•Press the [Cal] key to save any change of buzzer state and return to normal
weighing.
•Press the [Units] key to save any change of buzzer state and move to the next
setup parameter, which is to set the automatic switch-off time.
•If the buzzer is enabled, it will sound to acknowledge a valid key press or when an
error condition is displayed.
AUTO SWITCH-OFF TIME
•The default value for this parameter is “
OFF0 ” (auto switch-off disabled).
• The display will show “ OFFx ”, where x = 0 to 9 , representing the number of minutes
of inactivity, i.e. if no key is pressed for the specified auto switch-off time displayed
in minutes, the scale will automatically switch off. A value of
0 will disable the auto
switch-off, while a value of 9 will cause the scale to switch off approximately 9
minutes after the last key was pressed.
•Press the [Zero/Tare] key to change the auto switch-off time, with an automatic roll-
over from 9 to 0.
•Press the [Cal] key to save any change of auto switch-off time and return to normal
weighing.
•Press the [Units] key to save any change of auto switch-off time and move to the
next setup parameter, which is to set the enabled units.
@Adam Equipment Company 2004
9

ENABLED UNITS
The default setting for the enabled units is any of the available units i.e. Grams, Kilograms,
Ounces, Pounds or Pounds & Ounces.
NOTE: The currently-active unit cannot be disabled, hence to disable the current unit
an alternative unit must first be selected during normal weighing.
•The display will show the first non-active unit, together with “
On ”or “ OFF ”to indicate
its currently-enabled state.
•Press the [Zero/Tare] key to change the enabled state of the currently-displayed
unit.
•Press the [Units] key to save any change to the enabled state of the currently-
displayed unit and display the next non-active unit, together with its currently-
enabled state.
•Press the [Cal] key to save any change of unit-enable state and return to normal
weighing.
VIEWING ADC COUNTS
The ADC counts value may be viewed by holding the [Cal] and [Units] keys pressed
simultaneously at the end of the power-on display test.
The raw ADC counts as a number from 0 to 30,000 will be displayed, with 15,000
subtracted to give a displayed range of -15,000 to +15,000 counts.
This mode can be exited at any time by pressing the [Cal] key, at which point the scale will
return to normal weighing mode.
LOADING DEFAULTS
This function can only be performed by holding the [Cal], [Units] and [Zero/Tare] keys
pressed simultaneously at the end of the power-on display test, and should only be carried
out by qualified technicians.
Factory defaults will be loaded for the stored setup, zero and calibration values, then the
raw ADC counts will be displayed as described above.
@Adam Equipment Company 2004
10

@Adam Equipment Company 2004
11
This mode can be exited at any time by pressing the [Cal] key, at which point, since the
zero and calibration values have been defaulted, the scale will automatically enter a
calibration routine as described above. A calibration procedure must then be carried out to
ensure reading accuracy. It is therefore vital that a standard calibration mass is available
for this purpose.
A successful calibration at this point will return the scale to normal weighing mode, but any
errors will be unrecoverable, and the scale must be switched off and back on again to
allow the calibration to be completed. Normal weighing will not be possible until a
successful calibration has been performed after loading the default values.
ERRORS
During operation the software will attempt to ensure that the results obtained are sensible.
Potential error messages and their causes are detailed in the following table:
At power-up
ELo
A/D counts more than 10% of scale capacity below default no-load value.
EHi
A/D counts more than 10% of scale capacity above default no-load value.
Taring
ESt
Taring could not be performed because the readings were not stable.
No-load Calibration
ELo
A/D counts more than 10% of scale capacity below default no-load value.
EHi
A/D counts more than 10% of scale capacity above default no-load value.
ESt
No-load value could not be determined because the readings were not stable.
Full-load Calibration
ELo
A/D counts more than 10% of scale capacity below default full-load value.
EHi
A/D counts more than 10% of scale capacity above default full-load value.
ESt
Full-load value could not be determined because the readings were not stable.
Weighing
EOL
Weight is more than 0.03% (9d) above maximum range.
EOr
Result exceeds range of display.

@Adam Equipment Company 2004
12
QBW HARDWARE OVERVIEW
Power Supply PCB
This board converts the AC input from the mains adaptor to DC and provides a current-
regulated supply to the internal 6 volt battery for charging purposes, as well as to the main
ADC board. Two LED drive lines are also incorporated to provide battery charging
indication.
The incoming AC supply is rectified by the full-wave bridge rectifier BR1 to provide a raw
DC supply, which is smoothed by C2 and filtered by C3. This raw DC is then used to
supply a 14-pin DIL LM723 voltage regulator, which provides a voltage and current
regulated supply via the NPN series pass transistor Q2. The values of resistors R1, R4 &
R5 are chosen to give an output voltage of about 8 volts at the emitter of Q2. In order to
maintain this voltage, the voltage on the Vcc pin of the regulator must be a minimum of
about 11 volts. This means that the minimum input voltage from the mains adaptor must
be at least 9 volts AC or 12 volts DC.
The regulated voltage is then supplied to the battery and the ADC board via the 1.5 ohm
high-wattage resistor R3. When the current drawn through R3 exceeds about 500mA, the
voltage drop across it reaches about 0.7 volts, at which point the regulator begins to
reduce the output voltage, thus limiting the output current. The mains adaptor therefore
needs to be capable of supplying a continuous current of at least 500mA.
The voltage drop across R3, and hence the voltage supplied to the ADC board and the
battery will depend upon the amount of current being drawn from supply, which in turn will
depend upon the charge state of the battery. With a fully-charged battery, this voltage will
be about 7 volts, reducing as the charge current increases.
If the output voltage on the Zener diode ZD1 exceeds 6.8 volts, it will conduct, supplying
base current to Q1, which will turn on, turning Q3 on and Q4 off and supplying current via
R12 to the ‘GN’ pin on PL2, which will illuminate the green ‘Battery OK’ LED on the ADC
board.
If the output voltage on the Zener diode ZD1 falls below 6.8 volts due to the regulator
entering a current-limit state, it will cease to conduct, turning off Q1 and Q3 and turning on
Q4, supplying current via R13 to the ‘RD’ pin on PL2, which will illuminate the red ‘Battery
Low’ LED on the ADC board.
The ADC board supply is provided by PL2 pins 1 (positive) & 2 (negative), while the
battery is connected to PL1 pins 1 (positive) & 2 (negative), and protected by the fuse FS1.

@Adam Equipment Company 2004
13
Analogue to Digital Converter PCB
This board consists of four main sections:
1. Power supply regulation and monitoring.
2. Dual-slope analogue to digital converter.
3. Microcontroller and associated digital components.
4. LCD display and driver.
1. Power supply regulation and monitoring
The power for the board is provided in the form of a single DC supply (nominally 7 volts)
via CONN1 pins #1 (positive) and #2 (negative) from the power supply board. This voltage
is applied to the input of an LM2931 low-dropout 5 volt regulator via a series pass
transistor Q2, which allows the board to be powered up or down under software control.
When the [On] button is pressed, Q2 is turned on via R4, the microcontroller is powered
up, and its output on pin #1 is immediately set high by the control program, turning on Q1
and holding the power on after the [On] button has been released. When the [Off] button
is pressed, or the controller sets its pin #1 low, Q1 is turned off, turning off Q2 and
disconnecting the power until the [On] button is pressed again.
The output of the 5 volt regulator supplies the rest of the circuitry via separate digital and
analogue tracks, which are commoned together at one point only, via inductor L1. The 0
volt returns are also tracked separately for the digital and analogue components and
commoned together at one point only, via inductor L2.
Since the minimum voltage difference required across the LM2931 to maintain regulation
is about 0.3 volts, the DC input voltage to the board must be a minimum of about 5.1 volts
to maintain the required supply to the ICs.
If this voltage falls below about 5.25 volts, the output of the comparator formed by one of
the operational amplifiers in the LM324 (U5d) will switch high. This output is monitored by
an input on pin #17 of the controller, which will turn on the ‘Low battery’ indicator on the
LCD when this occurs.
A tri-colour common-cathode red / green LED is also mounted on the ADC board, with its
common cathode connected to ground, its green anode connected to CONN1 pin #3, and
its red anode connected to CONN1 pin #4. This LED is driven by two outputs from the
power supply board, but is located on the ADC board to allow it to be viewed through a
hole in the case next to the display.
2. Dual-slope analogue to digital converter
The load cell used for weight measurement is a strain gauge, which is connected to the
ADC board via the connector CONN3. Its excitation is provided by the analogue 5 volt
supply and analogue ground through pins #1 (E+) and #4 (E-) via the two inductors L3 and
L6. Since this excitation voltage is about 5 volts, and the output of the load cells used is 2
millivolts per volt, the output will vary from zero at no load to about 10 millivolts at full load.

@Adam Equipment Company 2004
14
This output voltage is connected via pins #2 (S-) and #3 (S+) of CONN3, and inductors L4
and L5, to the differential inputs of an OP-07 operational amplifier (U6). The cable from the
strain gauge is screened for noise suppression, the screen being connected to analogue
ground via CONN3 pin #5. Further noise suppression is provided by the filtering capacitors
C19 to C22, which are commoned to a mid-rail (2.5 volt) reference point, and resistors R37
and R38.
The input voltage from the load cell can be biased more positive by connecting resistor
R39 from the inverting input of the amplifier to the analogue 5 volt supply via solder bridge
SB2, or more negative by connecting resistor R40 from the non-inverting input of the
amplifier to analogue ground via solder bridge SB3. These solder bridges are used to
configure the desired offset for the different magnitudes of strain gauge used in the
variants of the QBW scale.
For the 1.5 and 3 kilogram scales, SB3 should be bridged and SB2 should be left open.
For the 6, 15 and 30 kilogram scales, both SB2 and SB3 should be left open.
Two different gains can also be configured for this amplifier by the use of solder bridge
SB1, which connects R32 in parallel with the fixed gain resistor R34. This is used to
configure one of two gains for the different magnitudes of strain gauge used in the variants
of the QBW scale.
For the 1.5 kilogram scale, SB1 should be left open.
For the 3, 6, 15 and 30 kilogram scales, SB1 should be bridged.
The output from this amplifier is fed into the inverting input of a low pass filter formed by
the operational amplifier U5a, which has its non-inverting input set to a reference voltage
of about 2.5 volts, then via resistors R25 and R24 into the inverting input of an integrator
formed by the operational amplifier U5b, which has its non-inverting input set to a
reference voltage of about 3 volts. The integrating capacitor C10 will therefore be charged
to an amplified and filtered voltage proportional to the output of the load cell. This voltage
is then applied to the non-inverting input of a comparator formed by U5c, the inverting
input of which is set at a reference voltage of 1.25 volts. The output of this comparator can
be read by the controller via an input on pin #8.
The PNP transistor Q4 is controlled by the output on pin #20 of the controller. Setting this
output low turns the transistor on, allowing the integrating capacitor to charge up towards 5
volts via R24. After the transistor has been turned on, the time taken for the inverted
integrator output voltage level to fall to the point at which the comparator output switches
low again depends on the voltage originally present on the integrator. Thus by switching
off Q4 for a fixed period of time, then turning it on and measuring the time taken for the
comparator to return low, a number can be obtained which is proportional to the load-cell
output. This number is read by the controller as an A to D counts value.

@Adam Equipment Company 2004
15
3. Microcontroller and associated digital components
The microcontroller used is a Philips 87LPC764 in a 20-pin DIL plastic package. This
interfaces with the other areas of the circuit as follows:
Using a serial I
2
C-compatible bus, the controller interfaces to a Philips PCF8576 display
driver chip (see below) and also to a 24C01 serial EEPROM containing 1 Megabit (256
Kbytes) of non-volatile memory. The serial clock (SCL) and serial data (SDA) lines are
pulled up to the digital 5 volt supply by resistors R14 and R15.
The port pins #1 and #17 are configured as output and input respectively, and are used to
interface the controller to the power control and monitoring circuitry as described above.
The port pins #20 and #8 are configured as output and input respectively, and are used to
interface the controller to the analogue to digital converter circuitry as described above.
Port pins #13, #14 & #15 are configured as inputs and used to detect key presses from the
[Tare], [Units] and [Cal] switches. These inputs are normally pulled high by resistors R11,
R12 & R13 and are then pulled low when a switch is pressed, which connects the input to
ground. The [On] and [Off] switches are connected directly into the power supply control
circuitry, and are not interfaced via the controller.
Port pin #2 is configured as an output, which is used to drive a buzzer via transistor Q3.
Since the reset state for all outputs on the controller is high, a PNP transistor connected to
the digital 5 volt supply is used, so that an output high state turns the buzzer off and
setting the output low turns the buzzer on.
Port pins #3 and #4 are connected via linkable headers to ground, and can be read by the
software for configuration or security purposes. If no link is fitted to the header, the inputs
are pulled high by internal pull-up resistors.
Pins #6 and #7 are left unconnected, as the internal 6MHz clock is used in this application.
4. LCD display and driver
The microcontroller is interfaced to the custom LCD display via a Philips PCF8576 display
driver chip, using the serial I
2
C bus. The serial data is converted to parallel data to drive
the display segments and backplanes. Since the display has 47 separate segments, and
the driver can only drive 40 segments on each backplane, the display has 23 segments
commoned to COM1, which is connected to the backplane #0 driver pin (BP0) and 24
segments commoned to COM2, which is connected to the backplane #1 driver pin (BP1).
The value of resistor R16 determines the clock rate for the display, a value of 150 kilohms
giving a clock frequency of about 100 kHz.
The interconnections between the segment driver output pins of the display driver and the
segments of the display are chosen for ease of programming, with each of the four 7-
segment digits and its associated decimal point being connected such that the data bits to
drive its segments all reside in the same display driver data byte.

QBW ASSEMBLY
LOAD CELL PREPARATION
Install 4 off M4 x 25 hex head screws, each with an M4 lock nut, into the 4 tapped holes in
the corners of the bottom frame.
Verify load cell capacity, mark top frame with unit capacity.
Verify load cell wiring colours.
Note the direction and location of the arrow on the load cell. See detail drawing.
Ensure that metal spacer is fitted between top of load cell and underside of top frame.
Attach load cell to both frames using 2 off M6 x 16 hex socket screw, shakeproof washer
and flat washer on each frame.
These must be tightened as much as possible without stripping the threads.
Isolate shield wire with heat-shrink tubing if this is not already done.
Install the M4 x 50 pan head underload screw through the top frame into the threaded hole
in the centre of the bottom frame, with an M4 locking nut between the frames.
Adjust screw so head is just clear of top frame and lock into position with nut against top of
bottom frame.
LOAD CELL TO BASE
All cables should be run under the load cell assembly.
Connect load cell to PCB assembly at CONN3:
Normal Alternate
Black pin 1 Red
Green pin 2 Blue
White pin 3 Green
Red pin 4 White
Shield Pin 5 Shield
Secure the load cell wires with plastic tie wrap or P clip to unused pillar near frame.
@Adam Equipment Company 2004
16

@Adam Equipment Company 2004
17
Model Load Cell
Capacity PCB Links No Load Display Counts Full Load Display Counts Span (FL – NL)
Min Max Min Max Min Max
QBW 1.5 3kg SB3* -7620 -3380 11460 19940 19080 23320
QBW 3 5kg SB1 & SB3 -10070 -6730 4960 11640 15030 18370
QBW 6 10kg SB1 -8210 -4790 7180 10600 15390 18810
QBW 15 20kg SB1 -10670 -6530 7960 12100 18630 22770
QBW 30 35kg SB1 -11470 -6930 8960 13500 20430 24970
* For QBW 1.5 it is necessary to change C16 from 10nF to 100nF. This can be done by
replacement or by putting 100nF in parallel with the standard 10nF.
INITIAL TEST
Apply mains power supply to unit and turn on.
Check battery voltage is 6.2 to 6.7V and increasing.
Observe the LED, it may be red if the battery is discharged or green if the battery has a full
charge. When power is removed it will flash red as the voltage disappears.
Place pan support and pan on the top frame.
Press [On] to turn on scale.
New PCB’s will detect that this is the first time the scale is active.
The display will show the A/D counts.
Acceptable A/D counts ranges at no load are shown in the table above.
Place a mass on the scale. The number should become more positive.
With full capacity on the scale the A/D counts should be between the values shown above.
Apply the full load to each corner of the pan in turn and adjust the corresponding overload
screw until its head just touches the underside of the top frame. Lock in position with the
lock nut against the top of bottom frame.
Move the full load to the centre of the pan and verify that none of the four overload stops
are touching the top frame and that the clearance is equal on each screw.
Remove the load and verify that the head of the underload screw is clear of the top frame.

@Adam Equipment Company 2004
18
Remove all mass, Press [Cal] key and hold for 3 seconds to initiate calibration.
Display shows “
C0 ”.
Press [Cal] key again and release.
Display will show “
tArE ”.
The display will then show the mass to be used, e.g. “
C 6kg ” for 6kg mass.
Place this mass on the platform.
Press the [Cal] key again.
Scale will calibrate then show the mass value.
Remove the mass, Verify the scale returns to zero.
Turn off the scale then turn it back on again after a few seconds.
Verify the calibration is still the same.
Turn the scale off and remove the power supply connector.