Unlimited Power !!

How to power LitSpin

After much thinking and looking at documentations, power transmission from static to rotating assembly will be done through ball bearings. Alexis told us he had used it before on other projects and that it would be suitable for our needs. We would transfer 12V power through one bearing and GND through another.

That meant that we needed one 12V->5V and one 12V->3.3V power supply rails. We also need 1.8V for the USB controller but we will use a basic 3.3V to 1.8V regulator.

How much ?!

Now that we know what voltages will be required, we need to find out how much current will be drawn on each rail.

Most of the processing will use the 3.3V rail. Here is the detail of how much power each component can draw at most. Figuring out the power consumption for the SoM is a little tricky. An FPGA’s power draw is tied to the processing done. A product page for a SoM similar to ours give an estimated max power draw of 4.2W for the SoC. We can estimate that with a 3.3V voltage input, it will draw around 1 300mA. That leaves the included SRAM and NAND flash. Using the datasheet for the chips used on the SoM, we can estimate around 400mA for both the RAM and ROM.

Componentmax current draw
SoM1 300mA + 400mA
uSD card200mA
USB wi-fi400mA
LED Drivers20x30mA
Clock buffers10x90mA

We come to a total of 3.83A at 3.3V.

For the 5V rail, the bulk of the power will be used by the LEDs. We will be using 1280 LEDs but due to the multiplexing, only 360 will be on at a given time. With 60mA per LED, that gives us a max current draw of 19.2A. The only other thing powered with 5V is the wi-fi dongle at around 400mA. We therefore need at least 20A on the 5V rail.

The regulators

Alexis suggested that we use the regulators that CyL3D used as the 3.3V current draw is similar to theirs and their 5V rail can give up to 50A. The detailed schematics will be in a next post regarding the mainboard.

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