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Some logic analyzer fun

As we want to synchronize our slave clocks using the XBee modules, we wanted to know what could be the difference in the reception dates between two slaves when the master clock broadcasts a “clock sync” message.

So I wrote a little bit code which toggled a GPIO when the message “clock sync” (0xAA) is received. The master firmware would emit 0xAA at 2Hz.

Then, I used a logic analyzer to observe the time difference between the two GPIO blinks.

Logic Analyzer

I found a mean difference of 60µs with a standard deviation of 55µs. I’ll let Issam & JB conclude (because they have far more knowledge in the localization part than me) but from my point of view, it seems to be fine.

2 comments to Some logic analyzer fun

  • I found a mean difference of 60µs with a variance of 55µs

    Are you really talking about the variance here? Because the variance of a time measurement is expressed in s², not in s.

    Could you give the maximum absolute deviation you have measured in addition to the standard deviation? If the maximum absolute deviation is bounded, the resulting error will probably be bounded as well.

  • ale6

    Ah yes thanks, I’m sorry. I was in fact talking about standard deviation.