Bar Code Scanners

APPLICATION NOTE
3312
Barcode Scanner
Bourns® Model 3312 trimmer. A better choice.
B
arcode scanners scan across a bar code and measure the intensity of the reflected light. The
light variation is converted into a digital signal.
Scan Light
Digital Signal
Figure 1.
Scanned Light and Digital Representation
A barcode scanner contains two basic sections. The first section is a scanner that converts the image
into a digital representation. The second section is a decoder, which combines the binary digital
signals into a series of characters. The decoded information is sent to the computer via keyboard or
serial interface.
Input Device
An input device accepts the reflected light and converts the optical reflection into digital/analog
signals. There are two major methods used for input; laser beam and CCD (charge-coupled device).
CCD scanners can be very small, but they have less depth of field than laser scanners.
Decoders
A decoder interprets the symbolic information and passes it to a host computer or stores the
information in memory. A decoder accepts the digital signal from the input device and converts it
to bars and spaces. Then it quantifies the element width and decodes the signal. Finally, it performs
character checks. After the decoding process is complete, it transmits the data to a host computer.
Decoders can be divided into two categories: on-line decoders and portable decoders. The on-line
decoder uses the power from an AC adapter or a computer and the latter uses a battery.
Trimmers
Trimmers are located in the laser diode driver and are used to bias and adjust the feedback of the
amplifier. Figure 2 shows a simple barcode scanner block diagram.
3312
Barcode Scanner
Bourns® Model 3312 trimmer. A better choice.
Glass
Receiving
Detector
RTC
USB Hot
Plug
ADC
µP
DCP
Single
Dual
Motor
Driver
DC
Motor
RS-232
Interface
Laser
Diode
Driver
Laser
Diode
Fuel
Gauge
Small
TFT/LCD
Display
Voltage
Regulator
Battery
Figure 2.
WLAN
Power
Management
Vref
Low
Noise
Amp
Battery
Charger
Barcode Scanner Block Diagram
DA1
R1
20
3
12
R5
1
R6
10
10
R3
20 K
1
R2
3
4 CTRL
1
LM317L_SO
IN
OUT 7
Laser Diode Driver Schematic
C1
PD
KT4
COMM
KT5
0.1 pF
100 pF
C4+
C3
100 pF
C2
15 K
R4
GND
Figure 3.
LD
VT1
KT3
+
0.033 uF
+
C7
C6
–VREF
4700 uF
KT1
+VREF
KT2
47 uF
BCP69
3312
Barcode Scanner
B
ourns® Trimpot® product line recently
released Model 3312, a 2 mm sealed
single-turn trimming potentiometer.
Model 3312 is well suited for space
restricted high reliability applications. The
sealed feature gives Model 3312 better
electrical parameters when compared to
its open-frame counterparts. Model 3312
is currently the only trimmer available in
10, 20 and 50 ohm total resistance values
for applications requiring small resistance
corrections.
Bourns® Model 3312 trimmer. A better choice.
SPECIFICATIONS
Electrical Characteristics
Standard Resistance Range
Resistance Tolerance
Adjustability
Voltage Divider
Rheostat
Resolution
Adjustment Angle
10 Ω to 2 MΩ
±20 % std.
±0.2 %
±0.4 %
Essentially Infinite
240 ° nom.
Environmental Characteristics
For more information on the 3312
and other resistive products from Bourns,
please visit
www.bourns.com
Power Rating (50 volts max.)
70 °C
125 °C
Operating Temperature Range
Temperature Coefficient
Vibration
Shock
Rotational Life
Americas: Tel +1-951 781-5500
Fax +1-951 781-5700
EMEA:
COPYRIGHT© 2008 • BOURNS, INC. 04/08 e/T0757
“Bourns” is a registered trademark of Bourns, Inc. in the U.S. and other countries.
Tel +41-(0)41 768 55 55
Fax +41-(0)41 768 55 10
0.1 watt
0 watt
-55 °C to +125 °C
≤100 Ω ±150 PPM/°C;
>100 Ω ±100 PPM/°C
20 G TRS ±1 %; VRS ±1 %
100 G TRS ±1 %; VRS ±1 %
25 cycles TRS ±3 %
Asia-Pacific: Tel +886-2 256 241 17
Fax +886-2 256 241 16
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