# A home security system has 15 sensors that detect open doors and windows.

#### Ansh Kumar

Joined Oct 28, 2018
5
Hey all,
I'm having trouble with this homework problem from my digital logic class.

A home security system has 15 sensors that detect open doors and windows. Each sensor produces a digital signal 0 when the window or door is closed and 1 when the window or door is open. The control for the security system is a microcontroller with eight digital input/output bits available. Each bit can be programmed to be either an input or an output. Design a logic circuit using dual 8-to-1-line multiplexer that repeatedly checks each of the 15 sensor values by connecting the sensor output to a microcontroller input/output that is programmed to be an input.

I would love to show you all the progress I have made, but I can't even figure out where to start. If someone could just point me in the right direction that would be fantastic.

#### ericgibbs

Joined Jan 29, 2010
12,919
hi Ansh,
Welcome to AAC.
As it is a Homework problem, we would like to see your attempt at solving the problem, then we can check your work.
E

#### Ansh Kumar

Joined Oct 28, 2018
5
sir please provide me its solution.
i have to submit it by tomorrow

#### ericgibbs

Joined Jan 29, 2010
12,919
sir please provide me its solution.
i have to submit it by tomorrow
hi,
We do not give solutions for Homework assignments.
If you want help, post the work you have done yourself in solving the problem.
E

#### wayneh

Joined Sep 9, 2010
17,152
sir please provide me its solution.
i have to submit it by tomorrow
Have you studied how multiplexing works? I think the problem will be much less daunting if you understand that piece.

#### jpanhalt

Joined Jan 18, 2008
11,088
" Design a logic circuit using dual 8-to-1-line multiplexer that repeatedly checks each of the 15 sensor values by connecting the sensor output to a microcontroller input/output that is programmed to be an input."

If I understand that correctly, you not only have to know that at least one sensor is high, but you have to know which one(s) and can use only one input? If true, then you need a synchronizing/timing clock. If you can use 4 of the 8 available MCU inputs, it becomes easier. Please clarify.

#### crutschow

Joined Mar 14, 2008
27,212
Do you understand how a multiplexer works?
That's the main step in solving your problem.

#### Ansh Kumar

Joined Oct 28, 2018
5
what will be the combination of output ?
not able to configure the circuit diagaram

#### Ansh Kumar

Joined Oct 28, 2018
5
Do you understand how a multiplexer works?
That's the main step in solving your problem.
what will be the combination of output ?
not able to configure the circuit diagaram

#### Ansh Kumar

Joined Oct 28, 2018
5
Have you studied how multiplexing works? I think the problem will be much less daunting if you understand that piece.
what will be the combination of output ?
not able to configure the circuit diagaram

#### wayneh

Joined Sep 9, 2010
17,152
what will be the combination of output ?
not able to configure the circuit diagaram
So two people told you the same thing and you chose to ignore both?

#### jpanhalt

Joined Jan 18, 2008
11,088
I thought this homework was due "tomorrow". Have you got an extension?

Here's a 4:1 implementation -- perhaps from your textbook, but it is a standard arrangement:

Can you write the truth table for it? Can you extend that to give an 8:1, which will use 3 outputs of the MCU and one input? Do you also have to write the code for the MCU?

#### Dodgydave

Joined Jun 22, 2012
9,953
Use a Max336 chip...

#### jayanthd

Joined Jul 4, 2015
906
2x 74HC151 and 1x 74HX386.