# Schematic drawings.

Discussion in 'Homework Help' started by Sakeru, Nov 30, 2008.

1. ### Sakeru Thread Starter New Member

Nov 30, 2008
3
0
i was giving a project on my engineer class. ( my first time)
i have to design a circuit.

the problem is written like this.
You have 4 inputs, 3 of them are switches, up (1)-down (0), and the doorknob. placing the switches in 1-0-1, and turning the doorknob, the door will open. You have 2 outputs, the alarm and the door opens. if the swtiches are not place in teh correct series, and you turn the doorknob, the door will not open and the alarm will go off. if its put in the right way, then the door will open and the alarm will not go off.

ive been trying to do it on my own, but its gotten to a point were i dont know what im doing. Right now we're studying gates, AND, OR, NOT, NAND, and well im was trying to figure out a way but couldnt.

if anyone could help me figure this out, it would be great help. ill post again, writting down the problem, as is written in my paper.

thank you very much, Sakeru.

2. ### leftyretro Active Member

Nov 25, 2008
394
2
Well I don't have the time to draw it out, but here is a verbal.
You need three two input AND gates and two NOT gates.

Sw1 goes to input 1 of AND gate 1
Sw3 goes to input 2 of AND gate 1

Sw2 goes to input 1 of NOT gate 1

Door switch goes to input 1 of AND gate 3

Output of AND gate 1 goes to input 1 of AND gate 2
Output of NOT gate 1 goes to input 2 of AND gate 2

Output of AND gate 2 goes to input of NOT gate 2
Output of NOT gate 2 goes to input 2 of AND gate 3

Output of AND gate 2 is the Door open command
Output of AND gate 3 is the Buzzer on command

3. ### SgtWookie Expert

Jul 17, 2007
22,183
1,728
We can help you with it, but we can't do it for you.

You must figure out how to use the logic gates in combination with the switches to turn the alarm off when the switches have been set to the correct position.

Some inverters with an AND gate (or maybe a few) will likely solve your problem, but it's up to you to figure this out.

4. ### Wendy Moderator

Mar 24, 2008
20,772
2,540
Are you having problems expressing a open/closed switch as a zero/one? If so think in terms of pull up resistors. Something like this perhaps.

5. ### blazedaces Active Member

Jul 24, 2008
130
0
Let me ask you a few questions.

1. What do you think is being described? Realizing this is, in my opinion, more important than all of the rest of the question... If you understand this, everything else should fall into place.

2. Do you know what truth tables are yet? Have you used state diagrams? Do both or whichever one you prefer.

That should definitely get you started. Good luck,

-blazed

6. ### Sakeru Thread Starter New Member

Nov 30, 2008
3
0
Thank you.

i just needed some help. i actually wanted to do it myself but couldnt figure it out.

thank you for your help. ill get to work now, XD hopefully i get it and do it
thank you.

7. ### Sakeru Thread Starter New Member

Nov 30, 2008
3
0
well yeah, i alredy know what a truth table is, but idont know how to use it in this situation.
like i said this is my first engineering class ever, and well im not really interested in electrical engineering, but i still wanna know for the future.

i understand the truth table, and the gates, but we've never done a problem like this.

i dont knwo wut a state diagram is, but i can always learn XD

well thank you guys, im still trying to figure it out on my own, i gladly appreciate your help. if possible tell me more about this "state diagram" or resistors.

thank you.