RoseOnRails – Good newS!!!


Yesterday and today, I spent a lot of time trying to resolve the big mistery of the UART communication between our nRF51822 and our STM32f103RE. Yesterday, we found out that actually, there was still an error in our board.h file for the nRF regarding the TX pin, which we corrected. But this wasn’t the error… I checked also everything in the Makefile, switched to the new verison of chconf, mcuconf anf halconf files (just in case), and checked in the sources of ChibiOS and the reference manual of the STM32f103xE that we had the right configurations. But when checking if the program entered the interrupt handler (by putting a breakpoint then by toggling a pin’s state), we got that the answer was no. To make it short, the signal was received on the RX pin but didn’t seem to be interpreted by the STM32.

Today, Sam gave me some precious advice to try and find out the origin of the “problem”. we used different techniques to make sure the RX pin wasn’t read correctly: first we looked at the USART1’s SR register’s RXNE bit by writing a function that returned this value, the RXNE was 0 ! Then we “mirrroed” the state of the RX pin towards another one (i.e. we toggled its state accroding to that of RX), the result was as expected (we saw the right UART signal with the correct timing -> 26us for 38400 baud). So what wasn’t working? We checked the clock as well (STM32_PCLK2 as the datahseet specified)…. then, Yann pronounced the word “remap” and it made Sam almost jump!! Actually, what we had forgotten to do was to configure one bit (yes, just one *** bit) to mention that our AFIO (pin 7) had to be remapped to the USART1_RX register!!!! Now it works… no wonder! I’m actually rather happpy to have learnt it this way, I’ll never ever forget it again in my whole life…

On Saturday nigt, Glesion and I spent quite a certain time thinking about how to deal with the electromagnetic and magnetic noise of the motor distrubing the Hall effect sensor. After discussion, we found out that the debouncing method wasn’t a very good one, since the perturbation is, in our case, continuous (it happens all the time, before and after the detection of he magnet) whereas the debouncing is a method used usually when the perturabtion occurs after you the event is detected. We then thought about shielding the motor with a metal case but Alexis said it would be too costly and diffciult. We thought also about a low pass filter, but its implementation in software would require too much calculus and power consumption for our nRF51822. The other idea was a hardware low pass filter. But before this, when discussing with Alexis, he suggested we first put the sensor as far away from the motor as possible (in order to avoid that the  magnetic field of the motor disturbs the sensro), and then, that we use a lower pullup resistance (this time, in order ot avoid the electromagnetic perturabtion). So we configured the pin as no pull and now use an external pullup resistance of 1.5kOhm (the internal oullup resistpr if the nRF51822 was much higher: 13kOhm). It still didn’t work as expected. So we finally, soldered a capacitor to have a hardware low pass filter and now it works as expected. Ouf! One less problem 🙂

What else?… Oh yes, after the LEDs worked, I completed the code of the central station to send commands to the ledstrip according to the encoding protocol that Yann defined (send <strip num>, then send <led num>, then <r>, <g>, <b>). In parallel, I wrote the Python function called from the Inteligence module to sned the 5 commands in one shot. The latter is still to be improved….

See you soon, gotta go make things work now… !



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