sd card swithing - Page 1
Forum section: electronics / general

author: colombo
author_rank: Newbie
timestamp: July 16, 2013, 07:39:40 pm
content: Hi I'm new here in the forum and need help in thisBecause it is not possible to connect one sd card to two devices atthe same timeI am looking for a solution that will allow me to switch between the card and two devicesSo I drew this -I need to switch the input lines (sd card) between output A to B that representing my two devicesI guess there are many controlers thet can do it - But I do not know much about itI'm looking for the least complicated option, the cheapest, and most reliable9 inputs / outputs are actually nine contacts of the SD card, some of which transmit information / identification / Powerhttp://pinouts.ru/Memory/sdcard_pinout.shtml(I do not know if I should use all the sd card pins)

author: fcb
author_rank: Super Contributor
timestamp: July 16, 2013, 08:17:10 pm
content: Unless you need to make this small or fancy reading up on the specification of the SD card and doing it using logic (perhaps you have a size constraint?) then I would be tempted to common the ground pins (2 of the 9 pins) and 4x BT47 type DPCO relays to switch between cards.

author: colombo
author_rank: Newbie
timestamp: July 16, 2013, 09:51:14 pm
content: Very interesting but it's too bigand it is not abut size as it is about simplicity4x BT47 are too complicated. this is too many elements

author: David_AVD
author_rank: Super Contributor
timestamp: July 16, 2013, 10:19:38 pm
content: Sounds like you need to specify your requirements more clearly. Size, power, cost as well as the reason for the switching.

author: fcb
author_rank: Super Contributor
timestamp: July 17, 2013, 12:51:21 am
content: Quote from: colombo on July 16, 2013, 09:51:14 pmSo it's not about size..... but it's too bigAnd four relays is too complicated...

author: amyk
author_rank: Super Contributor
timestamp: July 17, 2013, 11:48:49 am
content: http://www.fairchildsemi.com/pf/FS/FSSD07.html

author: mrflibble
author_rank: Super Contributor
timestamp: July 17, 2013, 06:30:31 pm
content: Use whichever cpld you happen to have lying around. Or lemme guess, while a cpld based solution is not too big, it is too complicated. And of course cpld's do not have banana flavor and as such fail to conform to your unwritten flavor constraint. Well, so much for an otherwise damn fine plan.

author: fcb
author_rank: Super Contributor
timestamp: July 18, 2013, 03:59:52 pm
content: I got the impression this wasn't a volume/commercial project, so getting the FSSD07 will be tricky.I always thought the fun bit was solving the problem yourself..

author: abyrvalg
author_rank: Frequent Contributor
timestamp: July 18, 2013, 05:13:03 pm
content: CPLD way is not so straightforward for this task, data lines are bidirectional and direction must be decoded from cmd line protocol.

author: mrflibble
author_rank: Super Contributor
timestamp: July 18, 2013, 06:09:55 pm
content: An FSM that keeps track of the CMD line is far more straightforward to implement than poorly specified man-in-the-middle-attack SD card multiplexers...You mention "this task" ... but right now we don't even know exactly what "this task" is.So I think I'll wait for clarification by the OP.Or maybe colombo is taking fcb's suggestion and is having fun by solving the problem himself.

author: David_AVD
author_rank: Super Contributor
timestamp: July 18, 2013, 10:38:02 pm
content: The OP registered and posted on the same day, so quite likely that we won't hear back until the next project. Seems to happen a lot (post and run).

author: amyk
author_rank: Super Contributor
timestamp: July 19, 2013, 10:44:07 am
content: Quote from: fcb on July 18, 2013, 03:59:52 pmYou can ask for some samples.

author: colombo
author_rank: Newbie
timestamp: July 19, 2013, 02:01:47 pm
content: Hello againI'm sorry that I didn't responded since I published this post. And sorry for my EnglishI really appreciate your effort to helpThe original purpose of this project is to connect one sd card to two computers using an adapterTrue. It's really simple and inexpensive to use two sd cards or perform some synchronizationBut I need to write&read the same sd card directly (without the use of network)At first I thought I just plug the card in to both computers by bridgingBut then I checked a bit and realized it was a problem from all kinds of reasonsEspecially because of the dual voltage supplying that can even cause damage to the computerThat's how I understood only other option is to switch the sd card between the two computersAnd perform this task seems to make more sense with a microcontroller Than using electronic components(It can be applied also to other memory devices and other machinery besides computers!!)I need that connection to be small. and if possible not too complex. as fore cost.. Lowest Of course.I want to mention - I have a general knowledge of electronics and a little less of microcontrollers(I studied electronics in college in my past. But I have not used it since)

author: fcb
author_rank: Super Contributor
timestamp: July 19, 2013, 02:13:56 pm
content: Relays... Relays... Relays...

author: colombo
author_rank: Newbie
timestamp: July 19, 2013, 02:57:06 pm
content: Relays look like a suitable solution Because it is straightforward and simpleBut (Based on what I found online) the amount of ports/entries is very limitedAnd as you said earlier - I would have to use at least four, or even moreAnd it will no longer be small or simple. This also increases the complexity and the cost

author: abyrvalg
author_rank: Frequent Contributor
timestamp: July 19, 2013, 03:17:36 pm
content: Be aware that you'll need to steer the "card present" signals also - the switching process must be seen as card removal on one computer and card insertion on the other (to trigger init/deinit, or there will be card state mismatch)

author: mrflibble
author_rank: Super Contributor
timestamp: July 19, 2013, 03:26:51 pm
content: Dumb question: what's the use case for this sd card switching thingy?

author: dr.diesel
author_rank: Super Contributor
timestamp: July 19, 2013, 04:08:45 pm
content: Quote from: colombo on July 19, 2013, 02:01:47 pmI'm curious, you can wire (SD card switch hack) between the two computers but can't use network? Can you explain why?

author: Crazy Ape
author_rank: Regular Contributor
timestamp: August 12, 2013, 11:36:07 am
content: You might find abilateral switchthat will do the trick.