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I am doing a traffic light design control circuit, so the light will change from red to yellow (for 3s) to green(for 12s) then to yellow(3s) , my question is how do when the light is green, how do I make it green for 12 s before turning yellow again. I was given a clock with 3s cycle.

Do I have to use J-K flip flop or counter ? Is there a way not to use it ? Because we wont be taught them until next week .

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  • \$\begingroup\$ What constraints do you have on the circuit? (This sounds like a homework question, so I'm guessing you can't use a microcontroller). What have you tried thus far? Add additional information to your post, not in comments. \$\endgroup\$ – uint128_t Apr 25 '16 at 15:20
  • \$\begingroup\$ Be aware that red to yellow to green is not a standard sequence, and for good reason. It encourages people at a red to get ready to jump forward on green, and this will encourage accidents. Yellow is warning for red. \$\endgroup\$ – WhatRoughBeast Apr 25 '16 at 15:41
  • \$\begingroup\$ Very hard to answer since we don't know the scope of allowable technologies: i.e. things you are being taught in the course. Unfettered, I'd go for a motorized drum contactor. It's lightning proof. \$\endgroup\$ – Harper Apr 25 '16 at 22:09
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Since this is obviously homework for a digital design class (or similar), there is a tradition on SE that we don't simply feed your the answer, but guide you towards it, so I'm not going to provide a counter or IC or anything, just some food for thought.

For me, this implies some sort of counter, although I'm sure that you can implement the counter using J-K flip-flops.

It looks like you have 3 states

green - 12s - 4 periods

yellow - 3s - 1 period

red - 3s - 1 period

If you look at the periods, you have a modulo 6 cycle (4 + 1 + 1) which could count from 0 -> 5. When the counter is 4, then yellow. When the counter is red, then 5. When not yellow or red, then green.

Good luck!

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If you won't be taught about digital circuits for a while, you could use three 555 timers hooked up so the red one would be on for 3 seconds, then when it timed out it would turn the green on on for 12 seconds, then when it timed out it would turn the yellow one on for 3 seconds, then when it timed out it would turn the red one on and start the cycle again, forever.

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