SparkFun Forums

[ping5]

Hello,

I had an idea today whilst trying to find my usb cardreader as i quickly filled up my SD card whilst taking pictures with my digi-cam. It would be nice to have a cable that acted like an SD or CF card but infact it was directly connected to a usb port, so that no data would be stored on the card, but be transfered transparently to a computer via usb, thus giving lots of storage.

There are many problems with this idea but i would like to see someone give it a try, professional photographers would love this idea, since they can have gigs of storage without the need to buy expensive SD/CF cards, just a cable, a laptop and a big hardrive,

One of the problems i can think off is that most camera don't like big SD/CF cards (over a gig?) so maybe it could be as simple a pretending its a 512mb card, but infact it never fills because once the picture is sent to the computer it stores it away so its no longer visable to the camera, so the card always has 512mb free space. Of course then you can't delete files from the cam it self, but its a good price to pay for gigs of storage.

Is this a workable idea? I've seen alot of amazing things come out of this community so i'm sure you can do something like this

thanks

[Philba]

it is certainly possible but several issues exist. speed will be slower, perhaps by quite a bit. being tethered to a computer, even if a notebook, seems more of a burden than a boon. SD cards are getting rediculously cheap these days.

[rod_vdb]

There is another major issue. With SD cards there are two ways to access them, paralell or serial.

Us hobbiests use SPI because the specs are released, however it is slow. Comercial SD stuff tends to use paralell because it is much faster, however you must pay for the specification.

High speed cards these days are hitting 40MB write speed, this is fairly difficult to acheive over USB and would almost certainly require a FPGA.

Some cameras can be connected to the computer by usb and save directly to the hard disc. Look out for canon's remote shooting software.

I know it is not exactly what you are looking for and I am sure that it is actually possible to do what you are asking but like most things it has some fairly trickey bits.

[bertrik]

I can see some practical problems... One of the main features of a digital camera (for me at least) is that it is *portable*, not tethered to a PC.

[daemondust]

Don't forget that the camera accesses the (usually) FAT16 filesystem on the card. You would probably have to powercycle the camera after "deleting" the files from the card since it's probably caching some of the filesystem information.

Why not have two sufficiently large (512MB 1GB?) cards and swap them between camera and a laptop set to automatically move the pictures? Two 1GB cards can be had for less than $45. The hardware required to make the interface you suggest would probably be much more expensive.

[prpplague]

I had an idea today whilst trying to find my usb cardreader as i quickly filled up my SD card whilst taking pictures with my digi-cam. It would be nice to have a cable that acted like an SD or CF card but infact it was directly connected to a usb port, so that no data would be stored on the card, but be transfered transparently to a computer via usb, thus giving lots of storage.

this is doable, in fact this is idea is basically what alot manufacturers use to test their boards that contain sd/mmc slots. when developing drivers for new boards, i use a FT2232 chip from ftdi . you can get pre made modules from http://www.dlpdesign.com . they do rs-232, rs-485, jtag, spi, i2c and gpios. this allows you to test and work with a wide range of devices. other devices that can be used this way are also the ezusb stuff http://www.elinux.org/wiki/EzUsb


so to summarize, it is possible to do what you are asking, but it might not really be practicle. these methods are really for debugging and testing, not really for solving a storage issue.

There is another major issue. With SD cards there are two ways to access them, paralell or serial.

Us hobbiests use SPI because the specs are released, however it is slow. Comercial SD stuff tends to use paralell because it is much faster, however you must pay for the specification.

just a side note, the SD Association has released a "brief" summary of the SD protocol as well some additional information on SDIO. it's not as detailed as what you would get from joining the association, but it is enough for most open source developers to make something usable.