Security card

Security is a very important issue. How do you stop unwanted access to high security areas?

Design a security card that allows a light to glow when it is inserted by the appropriate person.,

Obtain some thin copper metal, a pair of scissors and a match box.
Cut a piece of copper metal that just fits on the base of the match box. Cover the metal with tape and secure it to the base.
Using a sharp blade cut a pattern out of the sticky tape.
A simple pattern is shown on the right.
Prepare the cover by inserting two pins in places where they will make contact with a clear strip of metal when the card is fully inserted. Select the position of the pins carefully so that only when the card is fully inserted will contact be made between the two pins. Using a hot glue gun secure the pins to the container.

But this security card can easily can easily be duplicated. Connection between the two pins will be made if a clear piece of metal is inserted.

How do you overcome this?

*Hint - One way is to introduce a short circuit. By placing a third pin we can by-pass the light and cause a short circuit.

The complete circuit is shown on the left. The light glows only when the card with the specific pattern is fully inserted. Any other patterns either fail to connect the pins and complete the circuit or cause a short circuit.

Click to see a 120kb movie.

Can you identify the wire that causes the short circuit?

Identify the path of the circuit.

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