# Uni electronics work

Discussion in 'Homework Help' started by Makele, Feb 16, 2016.

1. ### Makele Thread Starter New Member

Feb 16, 2016
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0
My lecturer broke his hip and the stand in is struggling. I am stuck with this coursework and am pretty desperate to get this finished. I need to build a safety circuit using NOR gates. It is short and probably easy for someone with knowledge of circuits any help will be appreciated.

Question

A powered guillotine uses a motor to position the cutter. The cutter must not operate while the motor is running. There is a guard which must be closed and locked before the cutter can operate but there is a maintenance facility which will allow the cutter to operate with the motor stopped but the guard open. A traffic light system must be incorporated to show when the Guillotine is unsafe (red), safe (green) and when in maintenance mode (amber). The guillotine can only operate once when in maintenance mode.

Draw the Karno map and design the safety circuit using two input NOR gates (use as many as you require).

If each gate has a MTTF 1526173, calculate the MTBF for your circuit (in hours).

How could you redesign the circuit for an improved MTBF?

How could you achieve a MTBF of 1 × 109 hours?

What will the reliability be after 5 years?

(Show the calculations).

2. ### WBahn Moderator

Mar 31, 2012
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4,804
YOU need to show YOUR best attempt to work YOUR homework problem.

Make your best attempt and we can use that as a starting point. Then better the starting point, the faster things will progress.

We will NOT work your problem for you.

Johann likes this.
3. ### Makele Thread Starter New Member

Feb 16, 2016
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0
This is my truth table I made a circuit using AND gates but I don't know how to make it with 2 NOR gates

A B C Safety Expression

0 0 0 Green

0 0 1 Green

0 1 0 Amber B

0 1 1 Red BC

1 0 0 Red A

1 1 0 Red A

1 0 1 Red A

1 1 1 Red ABC

4. ### WBahn Moderator

Mar 31, 2012
17,777
4,804
The problem description appears to only mention one light that can be three different colors (or, possibly, three different lights, one for each color). Your seem to have a plethora of different kinds of red lights. What is the A, B, C stuff all about?

What are your inputs to the system?

What are your outputs from the system?

Where does the constraint of just two NOR gates come from? I don't see anything in your first post that imposes such a constraint, only that it must be built with NOR gates.

5. ### Makele Thread Starter New Member

Feb 16, 2016
8
0
At least 2 NOR gates my bad

A is the motor
B is the Guard
C is maintenance mode off

They are the inputs the output is whether the cutter will operate

6. ### WBahn Moderator

Mar 31, 2012
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If A is True, does that mean the motor is running or that it is off?

If B is True, does that mean that the guard is closed and locked or that it is not?

7. ### Makele Thread Starter New Member

Feb 16, 2016
8
0
If A is true (1) motor is running
If B is true (1) Guard is open

8. ### WBahn Moderator

Mar 31, 2012
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How are you going to deal with the requirement that the cutter can only operate once while in maintenance mode?

What defines "safe" and "unsafe"?

9. ### Makele Thread Starter New Member

Feb 16, 2016
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Amber represents maintenance mode, I don't know how you would put it only cutting once in maintenance in a truth table or circuit

10. ### shteii01 AAC Fanatic!

Feb 19, 2010
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Which means you need a bigger truth table.

11. ### Makele Thread Starter New Member

Feb 16, 2016
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0
How would I put it only cutting once into a circuit though?

12. ### WBahn Moderator

Mar 31, 2012
17,777
4,804

How would you do it if you were responsible for flipping switches to turn on lights or to enable the cutter?

You'd have to remember whether or not the cutter has been run since the last time it was put into maintenance mode. So you might write down the information that you needed to remember so that, at any given time, you could look at the status of the sensors A, B, and C and look at what you currently have written down and, based only on that collection of information, decide whether to enable the cutter.

You do the same thing here. How electronic circuits remember information is through the use of latches and flip flops (usually).