Hey guys,

I want to something like below for my project:
-User press ON switch (indicated by '1')
,if no user press ON for the last 7 seconds or more- Green light on
,else Red light on

-My attempt:
1. Create single pulse input from ON OFF switch.
2. Delay the input by using two shift registers. Give the parallel input the value of '0' (ground it) and the serial input will be from the ON OFF switch.
3. Check the first 7 outputs of shift registers whenever user press ON. if one of the outputs is '1' (meaning in this 7 seconds there is '1' input), Red light on; else Green light on.

-My concern:
1. Will the outputs of shift register have the waveform of the attached file?
2. Will the waveform ripple ,if there is no data input (meaning '0') and the clock input is still running?

-Additional question:
1. When we try to represent two states with '0' and '1', does this mean that '0' is ground state? In this case, if we manipulate output with logic gates, how could we differentiate whether there is an input or no input IF output is '0', or we cannot differentiate at all looking at the output, in this case '0'?

Lastly, thanks for any reply.

 

While it isn't a shift register, a 4017 (10 bit Johnson counter) will produce similar results. Do you think it would do what you want?

 

hmm.. did a search just now. it does give me what I want. but as a beginner, I wonder whether my concept is correct in my attempt. by the way, what is the advantage for choosing 4017 instead of shift registers?

 

Not much, except it fits the description you gave almost verbatum. A shift register might work better, but I know the 4017.

Have you read this?

LEDs, 555s, Flashers, and Light Chasers