Blinking Blues

Blink Does Not Work? 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 e6 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

In the image below the data from the arduino is being measured on channel 3, the test signal from the oscillator is on channel 5 and the rest are grounded or some sort of junk I have not gotten rid of. Click on it to go to a page with the image and then again to go full size which I did not do here to reduce the clutter. This measurement shows the good pulses. I typically use the sniffer cursors 1 to 4 for four consecutive good pulses. A good pulse is one very near the desired one, for example aiming at 10.00 ms I may get 10.120 ms. I actually expect some extra time ( perhaps not this much ) as there is some overhead in the routine. A bad pulse is typically off by much more ( 11.360 ms ). Bad pulses are identified by eye then tested using cursors 5 through 10. In both cases the good and the bad are consistent across many periods. The most consistent result is that bad pulses are separated by about 81.92 ms. And 81.92 / 16 meg Hz = 256 * some power of 10. That it comes out at the magic number of 512 seems very significant, but I am not sure why yet.

Bad pulse from the same test run ( or one with similar timings ):

More Results in Files

You can check out my results using these files or starting from scratch. I am still working on these timings so files may change, but I am putting up some versions now ( Jan 3 2017 )

• Arduino Code -- I keep adding to it, but the old subroutines that have been timed are not changed. It consists of 4 files that need to be unzipped into a directory called Blinkers and then opened with the arduino software. It is hosted on a google drive at: Blinkers
• Results spreadsheet: contains some of the measurements I have taken from the logic sniffer. It is in open office format. [1]
• Sniffer project files. They are all zip and hosted on a google drive at: [2]. These files can be opened with the logic sniffer software found at Logic sniffer software download

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

Blink is the Hello World of the Arduino. So would it be a surprise if it did not work? It sure surprises me. It does seem broken. Now in my case I am running it faster than the standard demo, but not real fast. I have tried a lot of code with a lot of variations, but for the basics:

   while ( true ) {
       digitalWrite( ledPin, HIGH );   // turn the LED on (HIGH is the voltage level)
       delayMicroseconds( 5000 );      // wait 
       digitalWrite( ledPin, LOW );    // turn the LED off by making the voltage LOW
       delayMicroseconds( 5000 );      // wait 
    }

If you think blink works please look at: http://www.opencircuits.com/Blinking_Blues and tell me where I went wrong. Insightful suggestions may be tried out by me. It would be nice to rebuild confidence in this iconic program