Available Photonics Experiments:

P5889 Bar code reader
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  • Types of bar codes
  • Diode laser
  • Rotating polygon mirror
  • Detection of scattered light
  • Bar code detection
  • Bar code recognition
  • Examples of investigations and measurements
OX Principle of operation
The key component of a bar code scanner is a rotating polygon mirror which deflects the laser beam. The beam passes a fixed mirror via a small hole. This mirror reflects the back scattered light from the target. A focussing lens is used to focus the back scattered light to the photodetector. If the laser beam hits a bright spot, the back scattered signal is high compared to the case when it hits a dark spot.
In this way the structure of a bar code is converted to a sequential electrical signal which is further processed.
OX General setup
A commercial bar code scanner (3) is modified in such a way that extra signals are brought to an external junction box (1). These signals are buffered by internal amplifiers and are available at BNC connectors:
(A) The BNC connector, marked as “RAW”, provides the direct analogue signals of the photodiode of the scanner.
(B) This signal represents the timely differentiation of the raw signal
(C) TTL signal formed out of the signal A
To read and display the detected bar code a PC pad (2) is provided which is connected via USB to the scanner (3). The software reads the data from the scanner after a scanning process and displays the code on the screen. A integrated database allows to store items with a related bar code.
Different bar codes can be generated with the software and printed as samples. These samples can also be used as measurement samples.
Number of active mirrors is reduced
Measurement sample
The commercial scanner uses five extra mirrors to enhance the active area of the scanner. For the measurement however it is better to reduce it down to one for a clearer structure on the oscilloscope and for sake of easiness. For this purpose the provided black sheets (A, B, C, D) are placed as shown on the figure on the left.
A sample of the oscilloscope track is shown beside it. The raw photodetector signal (A) and the TTL signal (C) are shown. The signal (C) can directly be compared with the used bar code sample.
  • P5889 Barcode reader (XP-2600) consisting of:
1ED-02701Barcode scanner interface
2TP-02101PC Pad
3TP-02601Barcode scanner
4XS-XP261Software Barcode Reader
 Required Options:  
 TP-01001Oscilloscope 100 MHz digital, two channel