Hi, I have to design a circuit which take input in terms of sound like on or off and switches on the electrical components like fan etc.. Help me in designing such circuit by only using logic gates.​

 

Not specific enough. Clarify.. It is impossible to answer your question.

 

see i have to design a circuit which take some voice as an input and switch on/off the fan take fan for an example !!! but the condition is that i have to use only the gates !

 

i dont know ho to be more precise....

 

I have a way you can be more precise..

"which take some voice as an input"

Does this mean through a microphone? Through a standard audio cable at audio signal levels? What voltage do you have peak to peak? At what level do you need to trigger a fan?

"switch on/off the fan"

What voltage/current is the load/fan? At what condition does the voice signal trigger the load/fan?

I don't see the correlation between using an analog signal input and logic gates. This lends itself to a filter/comparator type circuit, not using logic gates that work at specific voltage levels.

Steve

 

years ago i had to build a sound activated switch. The circuit i was given was a little useless because it did nothing to de-bounce the switching.

The first problem you will face is the small signal from a microphone will not be able to properly trigger a logic gate.

 

Is "use of only logic gates" an instructor imposed limitation, or does a valid reason exist?

 

You can make a Cmos logic gate or logic inverter into a mic preamplifier by adding a resistor in series with the input and a negative feedback resistor.

You can "cheat" a little by counting the spoken words instead of decoding the words:
Turn fan on. Fan off. But then the fan will turn on if somebody says, "Three Blind Mice".

 

You can make a Cmos logic gate or logic inverter into a mic preamplifier by adding a resistor in series with the input and a negative feedback resistor.

Very interesting! Does anyone have a link to related material?

Steve

 

http://www.fairchildsemi.com/an/AN/AN-88.pdf

Ken