RoseOnRails – still ledstrips, almost over!!

Hey hey!

Today we continued to find out the “apparently mysterious” reasons why our ledstrips didn’t work fully properly! Measuring the duration of our high and low SPI bits on the oscillosocpe we discovered that there were some “little” software bugs (for instance, with the help of Alexis and Sam we found out that since the idle state of the SPI was high by default, it was a better idea to avoid sending a 1 as first bit (else, the first 1 was longer than it should have been and we would send 100 instead of 000 to the first led hence some inexpected behaviour..). Sam’s great idea was just to place the reset at the beginning which very simply solved this problem.) On the other hand, Alexis advised us to first make sure that our experiments were compliant with the ledstrip’s datasheet, especially by making sure that our alimentation voltage was always in the [4.5V; 5.5V] interval. Since the SPI output voltage of the stm32f103cb is only around 3.65V, we did a simple montage to pull up the voltage to +5V (Since the montage is an inverter, our SPI now sends the logical inverse of the original buffer).

ledstrip ledstrip

Having solved this, there was much less randomness in the experiments!

Apart from the LEDs, we also discussed today in group about what had to be done from the software point of view. I did a brief explanation of the central station code done so far, and cleaned up our git repository a bit, adding readmes and comments.

At night, all four of us gathered to think about the Monday presentation and set the general layout of what we are going to say.

Then I worked on the Python code again a bit to clean it up and complete it.

As Yann said, tomorrow we’ll have to prepare the Monday presentation (of course, apart from doing some software since the LEDs have taken us too much time lately).

See you!


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