Blinking Blues

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Having some trouble with arduino blink. Will write up here. Draft now, not enough to really be of use to anyone but me.

Origin

I have been messing about with steppers and simple drivers for some time. Recently I put a logic analizer into use and noticed that the switching wave forms were a bit off. Simplifying this I went back to the basic blink and took a look at it. It also had some anomolies. This began an investigation of various blink code and the results. So far I have not found code that gives good results. In this investigation I am focusing on using pulses with half periods of 500 and 5000 micro ( not milli ) seconds.

Blink

What I Expect

The blinks I worked with for this investigation were all in the 1 to 10 ms or so period time frame. I used only the microsecond built in functions. I expected that the timings would:

  • be repeatable in the range of a few microseconds.
  • be accurate in the range of 10 to 20 microseconds.

What I Found

  • I found glitches in the waveform of up to 1 or more milliseconds ( 1000 microseconds )
  • Often the glitches would repeat every 81.92 milliseconds or so. Interestingly enough if I divide this time by 16 e 16 I get 512 which is more or less a magic number.

What I Tried

  • Different arduino boards
  • Different pins
  • Different implementations of blink
  • Interrupts on and off


Issues Investigated

  • Was the logic sniffer the glitched one: Do not think so, I generated a square wave on an ossicalator at 1KHz ( period 1 ms ) and looked for glitches in it. Nothing found.

Things Yet to Try

  • More boards
  • Different builds of the arduino software
  • More pin variations
  • Check unused pins, perhaps change all to output low....

Some Results

File:Measure1.jpg


More Results in Files

  • Arduino Code -- I keep adding to it, but the old subroutines that have been timed are not changed.
  • Results spreadsheet
  • Sniffer project files.

Test Setup

Logic sniffer is the dangerous prototypes single board device http://dangerousprototypes.com/docs/Logic_Sniffer_101

Measurement taken using the cursor measurement, finding some good pulses at the beginning and then visually scanning, then measuring for bad pulses later on. All recorded to a spreadsheet, that will be uploaded here.


Who I Told

Not Yet, but On My List

Links I Looked Over