555 Timer Turn Signals/Hazard Lights

Discussion in 'Homework Help' started by juddcharlesw, Nov 27, 2013.

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  1. juddcharlesw

    Thread Starter New Member

    Nov 27, 2013
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    Hello,

    I am attempting to simulate a hazard light/turn signal combo. I have implemented a 555 astable timer and one clocked J-K flip flop, as seen in my schematic attachment. I needed them to flash at different rates, hence the J-K to create a slower waveform. I am using the slower flashing rate from this J-K to drive the turn signals, and have the hazard lights connected directly to the 555 for a faster rate.

    I have both signals working independently at the slower frequency, and additionally have the hazard lights working at twice the speed of the turn signal flash. The problem is, when the hazard lights are flashing, I need the turn signal function to be disabled. Currently when the hazard lights are flashing and I turn on either turn signal, the slower waveform from the turn signal is seen in the LED output as well, creating a strange output frequency.

    I'm sure there is some simple logic here that I'm missing, but I just can't put it together. I need the hazard light to completely shut off the turn signal inputs when it is enabled. Thanks so much for any help you can offer.
     
  2. JohnInTX

    Moderator

    Jun 26, 2012
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    You could replace U3A/U4A with NOR gates and have the hazard input feed a 1 into the two new inputs. That would present a hard 0 on the inputs to U1A/U2A and block any signal inputs.

    You could also hold the JK f/f in reset whenever the hazards were on.
     
  3. juddcharlesw

    Thread Starter New Member

    Nov 27, 2013
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    Thanks so much for your reply. When I replace U3A/U4A with NOR gates it partially solves the problem. However, now the LEDs only work as long as the left/right signals are enabled. I lose the ability to turn the hazard lights on by themselves.

    How would you propose holding the JK in reset mode when hazard is enabled? Whenever I attempt this, since the hazard lights are a clocked output as well, it doesn't hold the JK in a permanent reset state, but pulses with the hazard light output frequency. I can only utilize the three switches that I have in place. Thanks again for your help.
     
  4. ScottWang

    Moderator

    Aug 23, 2012
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    74LS76(U14) is a TTL and its Vcc just for 4.75V~5.25V, if you over the voltage then it will damage the IC, and all other TTLs have the same situation.
     
  5. Wendy

    Moderator

    Mar 24, 2008
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    The owners of All About Circuits has elected not to host discussions of automotive electrical system modifications/enhancements due to safety concerns, the potential of legal ramifications and the possible circumvention of vehicle regulations at the state and federal level.

    This thread is against the AAC forum rules, Chapter 6, as seen here:

    This can be found in our Terms of Service (ToS)

    Automotive modifications of any kind are strictly forbidden. Therefore, this thread will be closed.

    Please try to understand the reasons behind this action, and feel free to browse and use the forums.

    You might find answers to your questions in one of these forums:

    http://forum.allaboutcircuits.com/showthread.php?t=54400

    Another good forum that shares many of the same membership is http://www.electro-tech-online.com/ . Good luck.
     
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