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Makahiya – I2C, a burning solution

Hi everybody,

First of all, Happy New Year. I hope that 2017 will be a wonderful year for you (or at least a not too bad one).

Since the beginning of the week, I’ve worked on… I2C ! Following the advices of Samuel and Alexis, I finally added the pull-up resistors and spied the communication with an oscilloscope. But this doesn’t help me to find the problem. And finally, I put the pins on OPENDRAIN mode, and it solved my problem. Such a stupid reason!!! It was due to an assumption I made during my first tests on the I2C: I thought that this parameter (opendrain) only deactivated the internal pull-ups. And in fact, it’s two completely different things… So yesterday evening, I managed to read and write registers of the capacitive sensor.

So this morning, I started to search for the proper values to set and implemented the initialization code. In parallel, I helped Tanguy on the Bluetooth module (because he also had communication problems). My initialization code was not perfect on the first try and I encountered strange behaviors, with the capacitive sensor sometimes suddenly not responding anymore. So I plugged and unplugged it many times. And once, I made a mistake on the connections. As I was solving problems, I didn’t see this one immediately. But after some time, I felt a strange smell, like smoke: the capacitive sensor was very hot. So I unplugged it, made some tests with Perceval’s help, and I’m quite sure that the sensor is dead… Less than 24 hours after the first communication, I lose my sensor… Bad news.

During the end of the week, I will work on the server, and I hope to have a working version before we receive the PCB (probably next Tuesday or Wednesday). For the capacitive sensor, I don’t know if it’s better to wait for the PCBs and continue the tests directly on the PCB or to buy a new evaluation board to finish the tests. This will be discussed tomorrow or Friday.

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