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