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Clock Syncronization

  1. Mar 21, 2008 #1
    Hi there,

    I have a clock at the receiver and I want it to be synchronized with the transmitter clock. For this reason, I send a short pulse to the receiver so that I know when a clock transition has to start.

    For the clocks I'm using the 555 timer. So far I tried experimenting with the reset pin on the 555 IC, however the results depend on the voltage of the capacitor wrt ground at the instant when I pull the reset to ground.

    I don't know if it makes sense, but I thought of forcing the voltage at the capacitor to a specific value (Vcc/3) while holding the reset pin to ground. Is this possible, so that when I put the reset pin back to Vcc, the action continues with having (Vcc/3) across the capacitor, hence getting the correct duty cycle?

  2. jcsd
  3. Mar 21, 2008 #2


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    Staff: Mentor

    555 timers are not going to stay synchronized for very long. To stay synchronized for some amount of time, you would use crystal-based oscillators followed by divide-down counters. You could synchronize the RX counter with your reset pulse.

    An easy way to make an oscillator and counter is with the 74HC4060. It includes a RESET signal input as well. Do you think that could work for you?
  4. Mar 21, 2008 #3
    Hey berkeman,

    Thanks for your reply. I think that the method you suggested does work. I will try it for sure especially because I've never used crystal oscillators.

    Regarding the 555 timer, I'm synchronizing it many times per second. Since I opened the thread I came up with the idea of operating the 555 timer at a higher frequency than required and using a frequency divider (4-bit counter) to reduce the frequency. In this way the error in the pulse width after the reset operation will practically not affect the final pulse-width (since its just one pulse out of 16). At the moment I'm working with a simulator and it does seem to work very well.

    Actually the 555 timer solution works on the same principle as the one you suggested but is less accurate than the crystal.

    Thank you
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