How to go about making LED light up only for 3 secs ?

brandy88 said:

Hi!

Very new to this field of study, there's so much to learn in a very short amount of time =)

I'm rather stuck in my design project.. 1st I havta input a 3-bit information using dip switch and push button to a circuit and after going thru numerous dencoders and magnitude comparator, a green LED is supposed to light up only for 3 seconds and not lighting up otherwise.. Have a 555 clock chip, and I've been thinking of using a counter of 3 beats but just couldn't figure out how to connect them...

Appreciate if any kind people can give me some guidances =)

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ericgibbs said:

hi,
Configure the 555 timer as 3second monostable, which is triggered by the output of the comparator.
To post a circuit we would need more info on the voltages, timing of the comparator etc...

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brandy88 said:

Hi Eric,

currently my 555 timer is running at 1 second period, n i'm using a 7805 voltage fixed voltage regulator.. Idea is from 3 of the 8 outputs from 74138 it will b directed to a LED which needs to light up for 3 seconds,
Up to here should work OK.
then goes on to store as '1 bit' information in a flip flop for 10seconds before being reset to 0..
Dont follow exactly what you mean

Can my circuit work?

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ericgibbs said:

hi,
Any chance you could post a sketch of your project.?

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brandy88 said:

sorry i oni have hand-drawn sketch, haven do up on schematics yet.. and apologies for the poor resolution, basically after passing the 3 outputs thru a NAND gate ( since its an either-or case for my design assignment, if the lower branch gives me a '1' i will get a '0' for my upper branch, which i haven finish my design ) my idea is using that output I can pass in to my counter to give a pulse of 3 seconds, den '0' otherwise to light up my LED..
den I will pass the '1' into a flip-flop ( which in the drawing is a counter, sorry again ) that stores a '1' for 10s and then reset to '0' after 10s..

but i cant help to feel my design is kinda naive =/

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ericgibbs said:

hi,
The design is too fussy [ I am being kind to you ...], dont worry we have all been there.
I have lightened up your sketch, give me time to thru it.

EDIT:
Looking thru you circuit, its difficult to understand what you are expecting the circuit to do.?

Post a full circuit with some explanation of its function.

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MrDEB said:

and where and what does the pushbutton supposed to do?
I can't locate the pushbutton?

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