Bar Code - Reader : Handscanner
school level
general theme
special theme
approx. 1 week
1 hour
10 min
Boys and girls produce a bar code-reader, and measure the electrical currents in dependence of the black or white pattern of a bar code.

  • phototransistor BPY 62-3 or other
  • bulb with lens 3.7 V
  • 1.5 V battery
  • 9 V battery
  • ammeter 100 mA
  • block of wood or plastic (approx. 70 mm x 25 mm x 25 mm)
  • black and white pattern
    EAN-barcode (Fig. 1)
  • wires
  • soldering iron
  • ruler and pencil
  • black paper
  • adhesive tape
  • drilling machine
  • grimlets 4 mm, 6 mm, 10 mm
Reasonable prized electronic parts can be  solved at mail-order business. Wooden and plastic parts can be bought at home  improvement stores. The teacher might already arrange for blocks to be sawed  according to the above  specifications.

1. Production of the reading head
A block of wood or plastic has to be sawed according to the above measurements, if not already prepared. Then, holes are drilled into the block with a drilling machine, as shown in Fig. 2 (measurements in mm).

If the opening at the bottom where both drillings converge is wider than 5 mm, black paper and adhesive tape may be used to tape it to a narrow slot (improvement of resdution). Then, two electric cirduits are produced, using a soldering iron and wires (Fig. 3).
After that the photo-transistor is placed in the 6 mm wide opening, and the bulb in the 10 mm wide opening. Additionally, a marking has to be put on the front side of the block, opposite to the slot at the botton.

2. Production of the bar code
You can copy the above EAN-code into DIN-A4 size, oblong format (best in black and white). Put a mm-scale closely below the bar code, beginning at the left edge of the sheet.

3. Reading of the bar code
Put the scanner on the top of the bar code, move it over the sheet in steps of 1 mm using the marking and thje scale, and read the respective currents.

The result is a transformation of the black and white pattern into a peaked curve of the currents in relation to the distance (measured values range between 10 mA and 40 mA). If the narrowest maximum is assigned to the value 0 and the narrowest minimum to 1, the result is a chain of 1 and 0 : digital information.

Instead of measuring the signal with an ammeter and drawing the measured values into a diagram, an x-y-writer can also be used in order to obtain the curve relating currents to distance. The soldering iron can be replaced by paper-clips and adhesive tape.

Methodical Advice
The extent of the teacher‘s preparations may vary according to the students‘ abilities. The making of the wood / plastic block may also be carried out at the same time in acts and crafts.
Coding and digitizing might be topics of interest in computer science and mathematics.
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