Digital logic design problem, please help!

Thread Starter


Joined Oct 18, 2011
In an industrial unit four motors M1, M2, M3 & M4 are in operation .The system in
Figure below consists of four manual on/off switches S1, S2 , S3 & S4 (to turn on /off
motors respectively) And control logic and motor drive interface. Design a control logic
that performs the following operation
• All motor are not allowed to work at the same time.
• Motors M1, M2, M3 are allowed to work at the same time.
• Motors M2 & M4 cannot be operated at the same time.
• Single motor can be operated.
• Motors M3 & M4 cannot be operated at the same time.
• Motors M1 & M4 can work at the same time.
• Consider all other cases don’t care except the above.
• Remember that the controller must shut down all motors for the conditions that
are not allowed.
Please draw or write
1. Truth Table
2. Circuit Diagram
3. Optimal Circuit
4. Problem you faced

Any idea on how to tackle this problem?


Joined Apr 11, 2010
Start by drawing the truth table...

Your problem actually provides the method of how to tackle this problem! Follow steps 1 through 4 for the data provided ;)

Thread Starter


Joined Oct 18, 2011
i know it does , i was racking my brain for the solution ,so i started drawing the truth table , and i am half way through it but i got stuck somewhere. When the problem says M2 AND M4 CANNOT BE ACTIVATED AT THE SAME TIME, does it mean that m2 and m4 are both 0's while m1 and m3 can be 1's or 0's right? like even if i draw the truth how will be able to figure the relationship out between the inputs and outputs? there are just too many possibilities , i guess i would have to do trial and error, correct me if i am wrong and thanks for the reply!!


Joined Mar 24, 2008
This is not a chat room, it takes time for people to respond. Try posting what you have done, you are more likely to get a response. Show the truth table you are stuck on.

The motors are either on or off. This is fundamentally Boolean in function. They are either a 1 or a 0.

One last point, if you read the requirements for the homework section no one should do your work for you, just show you where you are stuck and help you figure it out. If you think about it, it is the better of the two services.
I believe that when it says M2 and M4 cannot be activated at the same time it means that when S2 (the switch that controls M2) and S4 (the switch the controls M4) are both on or "1" then neither M2 nor M4 should be energized.