CRC must stand for Crazy Real Confusion

I’ve Come to a Reliable Conclusion upon working on CRC yesterday. Don’t try to understand what’s going on. Many walked this path before me, and yet I couldn’t look away at the promised cognitive pleasure of understanding it. In the end, I was denied this pleasure and here I am, left in frustration.

Well I might be a little bit exaggerating, but I’m sure that I’m miles away from having a grasp solid enough on CRCs to implement my own. For those who would want to do so though, this article from Barr’s group seems to stand as a reference, or at least a reliable entry point on the subject.… Read more

Working on communication data integrity

Lately I’ve been working on a way to make the communication between the STM and the ESP more reliable.

While searching on the subject, I came across two methods.

The first one made me reminisce some of the lessons we had in first year about information theory. The idea is to use a Hamming code for the messages of the protocol. This will make the communication more robust because of the properties of such a code. We plan to use a Hamming code (7,4) which means that the words will be 7 bits wide, with 4 bits of information (meaning we can go up to 16 different words, including the words with only bits at 0) and 3 bits of parity.… Read more

Catchin’ up with the posts

To hell those marbles

Last friday I mainly worked on getting the new marbles (the ones that hadn’t undergone any heating process) to the desired magnetic field values. Remember, on this post I had already manage to have the marbles we already heated at the desired value. It needed a heating time around 5 min, so I instinctively thought that for marbles that had undergone no heating, it would need a longer time. I was wrong. And not slightly wrong, but more like completely wrong.

So I started heating at 300°C for 6 mins, it was too much and the magnetic field almost completely disappeared (barely noticeable).… Read more

It’s summertime for our marbles (more like Venus’ summertime)

Wednesday I worked on trying to have all our marbles with roughly the same magnetic field, something around 20-40 arbitrary unit (as measured by the sensor).

After slightly changing the mount so I could have the marbles on a fixed point, I went on and measured the magnetic field of all our marbles. Because our marbles were heated with different processes we had a wide range of values.

With this montage the marble is centered and stationary over the coils and therefore above the sensor.

With this montage, I sorted the marbles going from 20-40, 40-60 and so on to 100-120 a.u.… Read more

Working on a pre-alpha v0.01 backbone

After finding a configuration that could do the job as discussed on the previous post, we needed to validate it.

To do so and as such, to decrease randomness and have the best repeatability possible, I started working on some kind of mount. After a little while I had a first version of this and did some measurement with the Hall sensor. I noticed that the positioning of the Hall sensor was unpractical as it was free to move.

That’s why I did some laser cutting and cut a hole to fit the breadboard in it in a wooden plank, just under the coils.… Read more

And if you still don’t succeed, try and try again

After trying to reproduce the results we had in this post we noticed some problem of repeatability. It was less frequent than the previous but still at a level we couldn’t ignore and that would cause future problem.

After working each on our own during the morning, I met with Alexis, Henri and Ilan in the E-lab/Fab-lab to further investigate the problem.

It turned out that we spent the afternoon testing dozens and dozens configuration. The parameters we changed were : spacing between marbles, marbles diameter, thickness of the plates we put the marbles on, material of the plates, stacking of the plates, using or not using little round metal plates (non ferromagnetic) to try to canalize magnetic field.… Read more

Flipping Test n°25158636

Back to our 2 marble-box

After enjoying nice holidays knowing we had a well working configuration and current value, it was time to get back on it and move further ahead.

Or we thought so. We tried to have it work again with the same values but it did not work. So we needed to some more tests.

Test test test

Alexis has told us to do some measures : we needed to measure the current rise time in the coil, the overvoltage and the voltage drop.

First of all we measured the overvoltage when brutally disconnecting the coil from the power source.… Read more

I have a coil. I have a current => I have a magnetic field ! Wait, do I ?

A naive first approach

We received the coils denominated SDE1006A-681K. These are 680 µH inductance coils.

We roughly soldered two wires on each pole of the coil as you can see on the image below for very basic testing.

Next we needed to connect it to the IoT node. As a very basic montage for testing, we configured user button with polling on the IoT node to drive one of the GPIO pin we have on high when pressed.

We used a resistance to limit the current output. As we wanted a current of the ordre of the mA we used a resistance around 1 kΩ.… Read more

Ah Qi, here we go again

After seeing Alexis, we noticed that the package of the previous component that we thought would do the job was based on BGA package… so we’re back to the previous step !

Basically the ideal component should :

  • be Qi compliant (low power profile and extended power profile)
  • have a 15 W power output
  • not have a BGA or CSP package which is definitely the hardest part

For a moment I thought I found the perfect match in the TS81000 : Qi compliant, up to 40W power output and QFN package ! Well yes, but actually no.

Alexis brilliantly pointed the fact that this component is only the auxiliary part of the receiver, and the other part which is the TS5111 has a WCSP package.… Read more

To Qi, or not to Qi, that is the question (that was actually)

About Wireless Power Transmission

Because we wanted to create a design centered around aesthetic for our device, we chose to implement wireless charging for our battery.

There are plenty of ways to implement WPT. First of all there is near-field power transmission and far-field power transmission.

For our project, we will focus on a near-field power transmission. In this field, one of the most common technique is inductive coupling. But it is not the only one : capacitive coupling is an interesting technique for our project.

Capacitive coupling VS inductive coupling

Because inductive coupling is based on converting AC current to a magnetic field, there is a high risk that it will cause strong interferences and perturbations with the magnetic fields of the marbles, thus complicating our control over our device.… Read more