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EXAMPLE LOGIC CIRCUITS - 2

V. Ryan © 2003 - 2009

 

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In manufacturing industry safe use of machines is very important. All machines should be set up in such a way that it is impossible for the machine operator to have an accident.

 

Machine ‘A’ is unsafe because it can be turned on and used when the guard is out of position, especially if it is operated by a machinist such as Ed the Handyman (website cartoon character). This means that the operator’s hands could be seriously injured by the dangerous blade as it cuts the material.


Alternatively, machine ‘B’ has been fitted with a logic circuit. It is designed to ensure that the guard must be in the correct position and the ‘ON’ switch is pressed simultaneously, before the machine will work. This means that the operator must keep his/her spare hand on the switch or electrical power will be cut, stopping the machine working.

   

   

 

   

The animation below shows what happens when the micro-switch has been switched 'ON' as the guard is in the correct position. This means that the logic states of both inputs are 1 (true, on, high, up), consequently the output logic state is 1 (true, on, high, up) and the machine works.
Remember, for the AND gate to output 1 both inputs must be 1.

   

   

QUESTION:

Draw a series of logic circuits that clearly show the logic states of inputs and outputs as the guard is put in the correct position and the 'ON' switch pressed.

   
 
   

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