Bar Code - Reader : Handscanner
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school level
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general theme
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special theme
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theoretical
level |
practical
level |
provision
preparation experiment |
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secondary
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optics
electrcity |
reflection
optoelectronic |
2
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2
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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.
Materials
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Preparation
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.
Realization
1. Production of the reading headA 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.
Evaluation
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.
Variations
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.
