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
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
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
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
We need to be able to drive our little magnet marbles and flip them according to a magnetic field direction or the opposite one. To do so current must be able to flow both ways through our self-inductances. Moreover we’re going to need current’s intensity of a much higher value than what is able to flow out of or flow in the GPIO.
One way to do so, is to use a H-Bridge as we can see on this site that we’ve already mentionned in an earlier post.
What’s an H-Bridge
Basically an H-Bridge is a electronic circuit built with drivable switches in a way that allows us to flip the voltage on a load and thus allows us to flip current polarity.… Read more