On Wednesday, I finished the PCB. I used one trick that found Alexis on our test PCB. We have two VCC, one for the coils and the other for all the other components. So, I create a two-parts plan. The VCC is in green and the VCC_COIL is in yellow.
I also have to route all the components. I found a way to make the routing easier, by enforcing a simple rule. When the route is horizontal, it must be on the top face, and when it is vertical, it must be on the bottom face. I also have to change the pins of the multiplexers in order to route them easily.… Read more
On Monday, I routed the 4×4 PCB I placed on Friday. I choose to put one multiplexer at the top of this cell and another one at the right. So the SDA lines (which come from the STM32, not from the multiplexer) will come from the left and the bottom. I also changed the scheme by removing a pull-up I put between the main multiplexer and the other multiplexers.
I try to use some shortcuts I found such as one that swaps the pins, but after reading the manual, I found that without a change in the part editor, I cannot use it, so I finally change the pins in the scheme
Now, I will copy 16 times this cell and continue routing with the other components
On Friday, I continued to place components. I spent some time to put the 4×4 coils precisely (in the same way as for the test PCB. I found some keyboard shortcuts that help me to do this quickly, but of course, I found the best shortcuts on Monday, when most of the work was done. I take a look at Alexis’ work he made on our test PCB and found some toolbars that will be very useful for me.
Now, I will try to place the multiplexer and to route it. Then I will copy this 4×4 grid sixteen times to finish the PCB until placing and routing the unique components.
On Monday, I began to have a look at a 16×16 device scheme. For this, I took the 4×4 scheme, I copied it 16 times, and I added two multiplexers. One that will multiplex the SCL signal to the multiplex that controls the Hall effect sensor, and one other that will multiplex the multiplexer that controls the H-bridge drivers. Then, I had some questions.
Should I keep a pull-up or a pull-down between two multiplexers or not? My answers for this moment is to keep a pull-up in order to avoid a clock signal on SCL if there is some latch between the two multiplexers.… Read more
After more tries on Tuesday, I found a way to flip the marbles vertically. I tried to use again the plastic part, without results. I make a huge comparison of all the configuration we tried before and at last, I shift a little the marbles from the coils, and with this, they flip in an easier way, even vertically, with a hole of 9.9mm. After finishing this, we can now concentrate on the PCB and the other problems of conception and programmation.
The shifted box is a box with the coils, a disk of metal, a 2mm plastic plank, a 3mm plastic plank (in green) with holes of 12mm of diameter, shifted of 5mm.… Read more
Zennedine finds a way to use our coils, so I tried to make a first box to check if it will not collapse. I made this and I checked if the marble flip or not, and it works.
Coils no more available
When we begin our project, we ship some coils, the 74458303 but in a short time, we cannot ship enough coils for the project. So I tried with the same configuration to use the 74458304 coils, and it works, even if there were more edge effect (the nearest coils flip sometimes). With these coils, we need only 0.59A… Read more
Before making our first device, we aimed at having a smaller one to test some components we do not have time to test: h-bridge, multiplexer, etc.
So, I had to complete a Test PCB that Alexis began. We already have chosen the components, and he chose the step-down converter, which we would use for our circuit.
I spend two days for placing and routing this PCB. We had two constraints: to put our coils at a precise place and the hall sensor just under them and to add the other component where there was still someplace. We choose to try to not add a battery since a phone charger can give us a 5V voltage with 1,5A current.… Read more
In my last post, I was a little sad. We were about to abandon the heart of our project: marbles because they were too powerful. Alexis gives us some hope by saying that we may have better result with some iron. So we try the configuration on the right (there is an iron plate between the two marbles), but it gives bad results. The iron does not constrain the magnetic field. It just attracts more the two marbles. We were about to try with some steel when the miracle came…
The miracle came from coils
In fact, the coils already have some iron on them.… Read more
In order to start testing our components (Hall effect sensors and coils), we needed to decide which board and which OS we will use.
Our project will not need to run any complex computation nor doing complex network communications. So almost all processors we checked could be used. We decided that it was better to take a controller little endian based on an ARM processor (because we are more familiar with arm’s instructions). We also wanted it to be low power and not too expensive. With those considerations, we went toward the STM32L475VGT6 because we already had boards at school with it.… Read more