Pros and cons of SD card versus USB memory stick for data logging
Don M
Posts: 1,653
I am looking at adding some data logging capabilities to my Propeller project. With the recent thread about "wear leveling" and life of the SD card media it got me to wondering which route would be better to take. I understand that there is a cost difference of adding just a socket and resistors (SD card) versus adding a socket and FTDI chip components (USB data logger option). I'm not concerned at this point with cost but more so with performance.
The data stream I'm looking to capture runs at 9600 baud and it is data that could be as short as 3 bytes or as long as 40 bytes. These data "streams" can happen as often as every 20mS.
Which format would offer the best performance and least trouble?
The data stream I'm looking to capture runs at 9600 baud and it is data that could be as short as 3 bytes or as long as 40 bytes. These data "streams" can happen as often as every 20mS.
Which format would offer the best performance and least trouble?
Comments
-- The SD card consumes less power and access is faster.
-- The USB data logger is finicky.
By that I mean you have the Vinculum monitor program in between your program and the USB stick. There is more to set up, more error conditions to handle, and the necessity for careful counting of bytes in each packet written. The Vinculum firmware is upgraded from time to time, which is a good thing, but USB keys themselves have variations. For example, some will not respond gracefully to the SUM or SUD commands to suspend operation for power savings. The internal operations of the Vinculum chip make it largely a black box.
There is variation in SD cards, but not so much, I believe, moreover the operation of Kye's SD driver and Tomas' FSRW are far more of an open book.