Design the simplest switch circuit from given truth table

Thread Starter

Rapper329

Joined Oct 7, 2022
7
Welcome to AAC!

Is this schoolwork?
Nop, Actually this is the circuit logic I want to implement for a bulb in my room. I want two switches for it. One switch outside the room and another one inside the room. Now what I want to be able is "When the switch outside is ON, the bulb must be ON regardless of inside switch. And the bulb should be off if the switch inside is OFF regardless of outsides switch.
 

Papabravo

Joined Feb 24, 2006
19,341
Nop, Actually this is the circuit logic I want to implement for a bulb in my room. I want two switches for it. One switch outside the room and another one inside the room. Now what I want to be able is "When the switch outside is ON, the bulb must be ON regardless of inside switch. And the bulb should be off if the switch inside is OFF regardless of outsides switch.
And a logical OR gives you that functionality, unless you can tell me a reason that won't work.
 

djsfantasi

Joined Apr 11, 2010
8,583
ABRequired Output
1X(don't care)1
X(don't care)00
That truth table can’t be correct.

Let’s say A = 1. Then the first row says the result should be 1 always, since the we don’t care about the value of B. But wait, if the value of B is zero, the result should be 0. Hence, we really do care about the value of B. But the first row says we don’t care…

The same argument (circular argument) can be made when B = 0…

So the truth table is wrong.
 

Thread Starter

Rapper329

Joined Oct 7, 2022
7
And a logical OR gives you that functionality, unless you can tell me a reason that won't work.
The problem with logical OR is when the switch outside is ON and switch inside is OFF, the bulb glows, but I want the bulb to be OFF in this case
 

Thread Starter

Rapper329

Joined Oct 7, 2022
7
That truth table can’t be correct.

Let’s say A = 1. Then the first row says the result should be 1 always, since the we don’t care about the value of B. But wait, if the value of B is zero, the result should be 0. Hence, we really do care about the value of B. But the first row says we don’t care…

The same argument (circular argument) can be made when B = 0…

So the truth table is wrong.
Thanks for pointing the mistake. I'd be grateful if there was any way I could implement the circuit I wanted.
If this circuit is somehow not possible, what would the corrected one be like for my requirement ?
 

dl324

Joined Mar 30, 2015
15,128
Thanks for pointing the mistake. I'd be grateful if there was any way I could implement the circuit I wanted.
If this circuit is somehow not possible, what would the corrected one be like for my requirement ?
You haven't given us sufficient information. Give us the output for all 4 input combinations.

"When the switch outside is ON, the bulb must be ON regardless of inside switch. And the bulb should be off if the switch inside is OFF regardless of outsides switch.
These requirements are in conflict. If the light should be on when the outside switch is on, regardless of the position of the inside switch, how can the inside switch affect the outside switch when the outside switch is on?
 

Thread Starter

Rapper329

Joined Oct 7, 2022
7
You haven't given us sufficient information. Give us the output for all 4 input combinations.

These requirements are in conflict. If the light should be on when the outside switch is on, regardless of the position of the inside switch, how can the inside switch affect the outside switch when the outside switch is on?
I tried but could not find another truth table that fulfills my requirement. Maybe I was trying something impossible. Sorry for asking stupid question.
 

michael8

Joined Jan 11, 2015
325
Could you tell me how this idea can be implemented using switch/circuits.
As a start it takes memory of:
a. the light state: on/off​
b. switch 1 state: on/off​
c. switch 2 state: on/off​
And then logic which implements the requirements... So it's not simple.
 

WBahn

Joined Mar 31, 2012
27,496
Nop, Actually this is the circuit logic I want to implement for a bulb in my room. I want two switches for it. One switch outside the room and another one inside the room. Now what I want to be able is "When the switch outside is ON, the bulb must be ON regardless of inside switch. And the bulb should be off if the switch inside is OFF regardless of outsides switch.
Completely contradictory specifications.

What if the bulb outside the room is ON and the bulb inside the room is OFF?

Your first spec says that the bulb must be ON while your second spec says that it should be OFF.

Which is it? Perhaps is should be ON since "must" is stronger than "should"?
 

WBahn

Joined Mar 31, 2012
27,496
The problem with logical OR is when the switch outside is ON and switch inside is OFF, the bulb glows, but I want the bulb to be OFF in this case
But you said very explicitly that if the outside switch is ON that the bulb must be ON regardless of the inside switch.
 
Top