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[SpiROSE] Last updates on the hardware, happy new year !

It has been time since the last update, I hope you had a good time with the New Year and holidays. Happy new year to everyone and I hope the best for every other ROSE project.

Since the last time I posted, we managed to finish the most important subjects in our work:

  • The last components of our projects have been chosen.
  • The hardware part is (at last) completely done.

MOSFET Driver

First, about the components, we had to choose a mosfet driver so as to have good switching timing. Indeed, we want to overdrive the LEDs so they are visible even if we don’t light them long. So we have to be very precise on the

However, the LEDs are connected to the +5V by their common anode, and to the mass through the LED driver. As we don’t have much place, we have to put the mosfet to the bottom of the LED panel, so it has to connect the LEDs to the +5V. Thus, we have no choice but using P-channel high side mosfet. Difficulties stemmed from this choice.

Actually, P-mosfet are bigger than N-mosfet, and as described by Vincent last time it has been difficult to put them on the PCB. But finding a P-channel high side mosfet driver is even worse. We finally end up with the LTC1693-5 from Linear Technology. It can drive a single channel but we can safely put eight MOSFET on each channel and still meet the timing requirement. It eases the wiring as we light eight columns at a time during a multiplexing step.

Basically, it was the only one MOSFET driver we found within our criteria, so there was no room for choice.

Card-to-card connectors

Then we had to find connectors between our cards. Our first thoughts went to single row 28-pin connectors with a spacing of 1,27mm between pins, with male ones being on the rotative base and female ones on the LEDs panel. However it failed to be routable because it put the flat angle brackets 0.85cm too far from the center, making the LEDs panel bigger than 20cm, too big to go to a pick&place machine. We hereby swapped them with dual-row 1,27mm 28-pin connectors (so 14-pin long) after computing that dual-row 2mm 28-pin connectors weren’t enough and failing to find smaller connectors.

What next ?

Next we will have to reorganize our PSSC for the software, as we noticed before the holidays that most of the time they were either obsolete or overlapped: one critera would ask the work for two and both would be validated at the same time, so there was no use of having them on their previous state. However most of the new plan has been done and accepted by the teacher just before the holidays.

We also have to finish SystemC tests for SPI and framebuffer, implement end-to-end SystemC tests (from SBC output to FPGA output).

We will probably not have the PCB before the end of the project but at least we will be able to show it for the final presentation, so software has to be tested enough so that we can focus on the hardware problems as soon as we receive them.

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