4553 Clock Pin - 2 Inputs?

Discussion in 'General Electronics Chat' started by CoachKalk, Jun 26, 2012.

  1. CoachKalk

    Thread Starter Member

    Sep 20, 2011
    139
    2
    I have a 5" LED Display that I have been working on. The final design will use a 4060/4013 combo to generate a seconds timer.

    While troubleshooting the display and waiting for additional 4060/4013 parts, I just used a quick 555 circuit to feed the 4553 clock pin of the 5" display. The 555 circuit and the 5" display play very nice together.

    For my laser maze project, I also have a smaller 1" display that I planned to keep track of the "hits" that occurred for the game.

    Finally to my question - could I send the 4553 clock pin of my 5" display both inputs?

    So if no lasers are tripped, the display would simply keep track of the seconds since starting. But, if the penalty trigger was set off, the timer would count off 4 -5 extra seconds, the pick up the 1-sec increments.
     
  2. elec_mech

    Senior Member

    Nov 12, 2008
    1,513
    193
    Hey CoachKalk,

    Let me see if I understand what you're asking.

    You have two circuits - one is a simple timer and one counts points (counter). If the counter is incremented, you want the timer to advance 4-5 seconds, correct?

    Off the cuff, I'd suggest adding two 555 timers or a 556. One to act as a monostable, the other as an astable. The astable would send rapid clock signals to the 4553 clock input. The monostable would limit the time the astable is on for and would be triggered by your counter circuit.

    As a rough first cut, the monostable could be set to output a 0.1 second pulse to the astable. The astable could then be set to output a frequency of 50Hz. Therefore, 5 pulses are sent in 1/10th of a second to the 4553, minimizing the odds of the counter and timer circuits sending a signal at the same time and making the 5 second time loss on the timer display to be instantateous.

    There might be an easier way to do this, this is just the first thought I had.

    I don't know if it would hurt to join the output of the astable to the clock signal into the 4553, but you can be safe by adding a signal diode such as a 1N4148 to both the clock and the astable output before entering the 4553 clock input.
     
  3. CoachKalk

    Thread Starter Member

    Sep 20, 2011
    139
    2
    Hey elec mech -

    I have a 1-second 555 monostable feeding a 555 astable cycles 5 times/sec. IF the clock pin would receive a signal from both the 1-sec "timer" and the astable 555, would one of them just be ignored? I will try out a faster version as you suggested as well.

    I was/am just not sure if I can double up on the clock pin. I will look into using 1N4148's. Thanks for giving me something to investigate!
     
  4. elec_mech

    Senior Member

    Nov 12, 2008
    1,513
    193
    The diodes will just prevent the outputs from feeding back to each other - they have no impact on the input to the 4553 (well, except the voltage being slightly less, but not enough to affect anything in this case).

    The worst case is the signals coming into the 4553 at the same time. In which case you might not see the 5 second loss at all. In the best case, the 555 sends the five clock pulses while the timer clock is low (within 0.5s). On average, there is a good chance the timer clock signal will be high in the middle of the counter signal and you'll only see a couple of seconds lost instead of five.

    I was originally thinking if you could increase the frequency of the counter pulses, you'll narrow the chances of hitting the timer pulse at the same time. On reflection, this only helps if a) the timer high pulse is reduced as well or b) you guarantee the counter pulses only occur during the low pulse of the timer. If you increase the counter frequency but do nothing else, then you'll see no change to the time if the counter pulses occur while the timer pulse is high.

    So, thinking upon this some more, if you could tie into the 555 monostable output signal and feed it to the reset pin of the CD4060 of the timer, you could disable the timer pulse altogether whenever the counter is tripped. Once the counter pulses are sent, the clock would resume. This may result in a second or so delay of your timer, but you can experiment and if a second of the total countdown time is really added every time the counter is tripped, just add another pulse to counter to compensate. The greater the frequency of the counter pulses, the less time the monostable needs to be on, the less likely you are to add much, if any, time. Hope this helps.
     
  5. CoachKalk

    Thread Starter Member

    Sep 20, 2011
    139
    2
    elec mech - Thanks for the input. Just reading through your ideas, I think you may have given me an idea.

    Since this project is strictly for fun, the exact time is not that important. As long as the method is consistant for each kid.

    So, I think I can just use the arduino to shut "off" the timer if/when a laser is tripped. Then, turn in back "on" after the penalty is added. I suppose a second or two may be lost in the process over the entire run, but the desired addition of the penalty time showing up will be more than worth it.

    Thanks again for being willing to contribute to this never ending process.
     
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