# Need Help in Digital Electronics

Discussion in 'Homework Help' started by aniskazi, May 3, 2014.

1. ### aniskazi Thread Starter Member

May 3, 2014
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0
Hello This is the question I'm having trouble in... My exams are next week I have solved most of the problems but I can't do this one guys so can anyone help please.
A jet aircraft employs a system for monitoring the rpm, pressure, and temperature values of its engines using sensors that operate as follows:
 RPM sensor output = 0, only when speed < 4800 rpm
 P sensor output = 0, when pressure <220 psi
 T sensor output = 0, only when temperature < 200˚F

Figure 2.1 shows the logic circuit that controls a cockpit warning light for certain combinations of engine conditions. Assume that a HIGH at output W activates the warning light:

(a) Create your truth Table with appropriate input-output combinations
(b) Determine what engine conditions will give warning to the pilot.
(c) Using K-Map technique to obtain your simplified Boolean equation.
(d) Change this circuit to one using all NAND gates and constructs the circuit.
This is the image.

http://postimg.org/image/fydv4resp/

2. ### MrChips Moderator

Oct 2, 2009
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3,451
Show us your work for each step (a) to (d).

3. ### aniskazi Thread Starter Member

May 3, 2014
44
0
Hey I'm confused in the first two parts... about the truth table I know that there are three inputs
RPM ,P and T
so the total input conditions will be 8 but I can't understand that how can
I see wether the speed is < or > 4800rpm and the second part as well about what engine conditions will give the warning the rest two parts I can do by myself and I'm only asking for an idea to solve it

4. ### djsfantasi AAC Fanatic!

Apr 11, 2010
2,900
874
That is the purpose of the sensors. The output from the RPM sensor will tell you if the speed is < or > 4800 rpm. Same for the other conditions.

Common sense should get you the second answer. If not, the supplied diagram deserves a look.

This should get you past the first two questions.

5. ### WBahn Moderator

Mar 31, 2012
18,085
4,917
As Mr. Chips said, show us your work!

If the RPM sensor is 0, what does that tell you?

If the RPM sensor is 1, what does that tell you?

6. ### aniskazi Thread Starter Member

May 3, 2014
44
0
Hey thanks for the fast reply guys.
Well here is what I've done I have made the truth table and than I used the inputs from the truth table in the circuit and what ever output I was getting in the end I was putting it in the truth table (a) part done and now in the b part If I want to give the pilot a warning I need highs on T P and RPM?

7. ### WBahn Moderator

Mar 31, 2012
18,085
4,917
Saying that you've made the truth table doesn't tell us anything. SHOW YOUR WORK!

8. ### aniskazi Thread Starter Member

May 3, 2014
44
0
T P R Output
0 0 0 0
0 0 1 0
0 1 0 0
0 1 1 0
1 0 0 0
1 0 1 1
1 1 0 1
1 1 1 1

This is the truth table that I've made I used the inputs in the fig and got the oupts.
and I guess now the (b) part will be to take all the 1 outputs form an euqation simplify it and than make a logic circuit? or no?

9. ### tshuck Well-Known Member

Oct 18, 2012
3,531
675
You should look over your results again, particularly around 100.

Part b seems to be asking just that you identify and list which sensor conditions would result in the warning light being illuminated. It may want you to list the values as minterms, or a Boolean expression. Given the next question, it may want you to derive the Boolean function from the truth table, then simplify it in the following step.

Part c is where you simplify the logic.

Last edited: May 6, 2014
10. ### aniskazi Thread Starter Member

May 3, 2014
44
0
so the warning light will be on when the output is high so I jsut have to tell when the output will be high as the last three outputs are high so they will make the warning light high so that's my answer right?

11. ### tshuck Well-Known Member

Oct 18, 2012
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675
Once you have a correct truth table, you should make a Boolean function that describes when the warning light is on...

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12. ### aniskazi Thread Starter Member

May 3, 2014
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yes corrected the truth table

t P R OUTPUt
1 0 0 1
1 1 0 1
1 1 1 1

so i got the eq: T P' R' + T P R' + TPR
correct?
I tried to simplify it:

taking TR' as common I got TR'(P' + P) + TPR
since(P' + P)=1
TR' +TPR ?

13. ### WBahn Moderator

Mar 31, 2012
18,085
4,917
It's already been pointed out that your truth table in Post #8 has a problem. So fix that (and don't edit Post #8 since people have referred to what is already there -- instead post an updated truth table in a new post) and then let's continue.

It might help if you start converting your logic diagrams (the simple ones) into word phrases. For this circuit, it would be something like: The warning light is on if the temperature is high AND either the oil pressure is high OR the rpms are low. Compare that sentence to your truth table.

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14. ### tshuck Well-Known Member

Oct 18, 2012
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675
Part c asks you to use a K-map, specifically, to do the simplification...

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15. ### aniskazi Thread Starter Member

May 3, 2014
44
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okay and so my b part wants to know just that when the warning light will be on so it will be on when I got highs in my output in my truthtable so the answer is:
When Temp will be high and press or RPM will be high the warning light will get a high at the output giving a warning to the pilot.

16. ### tshuck Well-Known Member

Oct 18, 2012
3,531
675
I think it might want you to describe it in terms of the pressure/rpm/temperature values given, e.g. "if the RPM is less than 4800 while the pressure is less than 220 psi and temperature is above 200°F, then the warning light will be..."

Your last statement is wrong - what happens if temperature is high, pressure is low and RPM is high?

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17. ### aniskazi Thread Starter Member

May 3, 2014
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okay I guess I will just give a separate statement for each high output just like you mentioned above
if temperature is high, pressure is low and RPM is high than my output will be a low and there will be no warning like that ?

18. ### tshuck Well-Known Member

Oct 18, 2012
3,531
675
You needn't do a separate statement for each row in your truth table, i'm just pointing out that since the information is presented, you may want to respond with the numerical values that the signal states correspond to.

... What does your truth table say?

Look at the bolded words:
What happens when RPM is high? Your statement implies that if temperature and RPM is high, the output is high - is this true? Is this always true?

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May 3, 2014
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