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Much of our modern technology is a "black box." This expression refers to the fact that most of the operations happen out of sight of the user. We push the buttons on the remote, and the TV channel changes. How does pushing a button change a channel? The average user doesn't know. When the "Check Engine" light goes on, how does the car "know" that something is wrong? In each case, a set of sensors send a signal to a microprocessor, which is programmed to react to different combinations of inputs. Someone has the job of thinking through all of the possible combinations of possibilities. This logical analysis results in a computer program, which then gets translated into an electrical circuit that actually does the job.


Your assignment is to build a Friendship Detector that uses battery power to produce an output (sounding an alarm, lighting a bulb, moving a motor, or some other electrical output approved by Mr. Cox.
  • The device must have three or four input switches clearly labeled with binary questions.
  • These questions should be strategically chosen so that a "yes" answer meets one of your conditions for friendship.
  • The device should be in a closed container, with only the switches visible.
  • When demonstrated to the class, the device will yield an "on" or "off" output depending on the answers of the tester.
  • You must work alone.
  • Your Machine must incorporate three or four input switches, one electrical output, and a logical connection among them.
  • The sum of the height, width, and depth of the project must be less than 75 cm.


  • You must show a logic diagram for the Detector on Tuesday, May 5.
  • You must show a wiring diagram for the Detector on Tuesday, May 12.
  • You must demonstrate the Detector in class on Tuesday, May 19.


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