Moving code from ESP8266 to ESP32

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A while ago I made a mashup of Dan Royer's code CNC 2 Axis Demo with my own code for trapezoidal motion stepper and servo control for ESP8266.

I assumed porting the code to the ESP32 would be trivial, and that was true for the most part: changes like library name being Wifi.h instead of Wifi8266.h were not a problem. UDP now does not like multicharacter writes but you can use print instead. So far so good.

However, when it came to the interrupt code I was stuck with the stepper interrupt causing an exception sometimes. And to make things weirder, the servo interrupt worked flawlessly (both of them had the IRAM_ATTR directive if you ask me).

Going little by little, I could narrow down the culprit to a floating point operation during the interrupt, that would cause problems sometimes but not always. Browsing around I found this post. Where the solution was simple: do not use floats within the interrupt routines but doubles. The reason was the float calculation would be performed by…

Decoding barcodes from scanned pages

A while ago I created a tool that would send the marked exams to my students by email. I used adhesive stickers with a QR barcode they put in the first exam page once they are done. The system kind of works and even some colleagues have started using it too. The problem is that once we have the pile of marked exams scanned as a single PDF file, barcodes need to be read reliably.


It is not that the scanned images are bad. I usually scanned it at 200dpi grayscale. The problem is that even if I set the black to the strongest setting is not good enough for ZXing library to decode it properly. And of course if the code is not decoded properly all the system goes under.

For a while I have been cranking up the black color using Imagemagick command line tool and when that was not good enough I realized that blurring the document would also helped. While I get that working, the exam itself became not so nice to read after that.

Anyway, after a bit more of testing I realized that the slight imperfections on the dark areas of the barcode seemed to be the cause of not being recognized properly, so I did a quick test with The GIMP to see if Erode operator would help here.

Erode will use a mask around pixels that will keep the blackest neighboring pixel, effectively eroding white pixels, mostly those surrounded by darker pixels. A blur operation later would make the result even better for much more reliable recognition.
So the question was now to just do this in an automated way. As I was already using ImageMagick I googled to see if that feature was available in it. But several posts on different forums suggested it was not possible.

So the next few hours I fought with The GIMP command line mode. It is there, it can be used, but I am embarrassed to say I kind of gave up as I failed to see how I could do that quickly and easily; after all I just wanted to use a couple of options of the filter options (erode and later blur using default parameters). Some examples I found online did not work at all with 2.8 version, maybe something has changed since they were written. Finally I decided that it might just be easier to code that in Java.

But just by chance, I discovered that what new versions of ImageMagick call Morphology Methods do, in fact, include an erode operation. So finally it is all good and I get a, hopefully, reliable barcode decoding.

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