[LASMO] Storage devices

LASMO will need to get data from the storage devices where the animations will be stored. For that reason, we need to add to our PCB a USB connector and a SD connector, as well as identify the electrical needs of the devices once connected and active. So I looked for what kind of SD cards and USB drives were fitted for LASMO. (streaming of  ILDA files). Thanks to Pierre, we know that we’ll need a debit of approximately 500 kbps.

SD card

SD cards are divided in 3 categories according to their storage capacity, and are granted a speed class among 11 possibles. 

https://www.sdcard.org/developers/overview/speed_class/

According to this table, all the speed classes on the market are fitted for the application.

As for power supply, it is kind of standardized. Indeed, accessing SD cards with an SPI bus requires a voltage of 3.3V. After looking at the cards available for example on Mouser, the typical supply current is between 30 mA and 100 mA. 

USB drive

Thanks to the presentation on USB we had a moment ago, we know that USB 2.0 and USB 3.0 deliver theoritical debits up to 480 Mbps and 5Gbps respectively. That is largely enough for what we need.

We had arguments over which type of connector will be the best (between USB-A and USB-C) . We finally decided to go with the most common (for the moment) USB-A.

As for the power supply, if the voltage is almost always 5V, the current does change with the version of the protocol: maximum 500 mA for USB 2.0 and  maximum 900 mA for USB3.0.