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About Sphero and Irda

Today we returned to normal course after the Athens week.

Already in the morning teachers asked us where we were, what we have done and gave us some advices on our organisation.

We updated our pssc according to our new and final objectives, better late than never. There are some points we need to cover before rushing into the project. First of all we have to finish as fast as possible the pcb for the course in order to work on ours. We were asked to deliver it for thursday, that gives us 3 days to do it. It’s scary but since our pcb won’t be much complicated we hope we can do it.

The components must be chosen fast, we already settled on the mpu : the STM32F405RG, we will use a 3 axis magnetometer, the same IRDA chips as on MBLED: TFBS6711. The same buzzer as on the dev board.  Some small rgb leds, an IR photodiode  etc.

Today I worked on some issues we hadn’t solved since a long time, here are the answers of those questions:

  • To what is plugged BOOT0?  A pull down to GND via a 1k resistor  R6. If you want to boot on system memory you just have to remove R6 and connect the pin to VCC.
  • Why do we measure a 2Ohms resistor between mstby (motor standby) and gnd?  There is a short circuit somewhere, we weren’t able to find it, it explains why we can’t control the motors anymore.
  • Where are the resistors between bluetooth uart and the mpu uart? Answer is R5 and R4. (see the picture).
  • Does IRDA goes through the transparent shell?  YES!  But not through sphero’s white plastic shell.
  • Can we measure distance by measuring the reflected beam on RX pin on the IRDA chip? NO, there is always the same signal as tx on the rx pin during emission.  It means irda isn’t really full duplex.

About Irda: We weren’t able to make a simple chibios program work on the MBLEDS, I decided to give a try at recompiling one of their original program, i just had to find the right branch on git, master was the deal.  And i tested the snake program with a transparent shell between 2 mbleds, it worked fine. I also made measurements on the RX and TX pins of ther irda, to see if we can measure the reflexion, we can’t.

I made a picture of sphero’s pcb in order to summarize the important connections we found on the board.

Simply testing emission and reception

Simply testing emission and reception

Sphero bottom board with light annotations

Sphero bottom board with light annotations

Sphero's pcb Top layer with annotations

Sphero’s pcb Top layer with annotations

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