FEDEVEL
Platform forum

Anik , 07-27-2024, 07:16 PM

I want to access a same SD card from two deivce. And I thought about this with relay. I can use 4 DPDT relay. But this device willbe very big. Is it possible with any other way?? Like if I use Multiplexer/Demultiplex IC for it. But it must be all pin bidirectional. Please give me any better suggestion.

Anik , 07-27-2024, 07:17 PM

https://www.lcsc.com/product-detail/Signal-Switches-Multiplexers-Decoders_Texas-Instruments-SN74CBTLV3257DBQR_C481393.html

IC link

QDrives , 07-27-2024, 07:53 PM

Robert made a video once on his 3D printer to add WiFi to it. That was a SD card too.
However I cannot find it.
But yes, I would guess that simple logic buffers can be used for it.

Anik , 07-27-2024, 07:59 PM

Yes I have seen the video maybe year ago. But it need to be simple. And full speed configuration of SD card.

Anik , 07-27-2024, 08:00 PM

And about the buffer I could not found and bidirectional IC. Everyone is Unidirectional

QDrives , 07-27-2024, 08:07 PM

Which signal is bi-directional?
What about analog switches?

Anik , 07-27-2024, 08:08 PM

Read write on SD card, is there not need bidirectional?

QDrives , 07-27-2024, 09:30 PM

But do you want to access it from two devices at the same time?

Anik , 07-28-2024, 01:34 AM

If possible at the same time willbe better. Otherwise there willbe a switch to change device.

Robert Feranec , 07-28-2024, 03:16 AM

there are chips for this. I started working on similar project, but I had no time to finish and tweak it, but I did manufacture the board and works ok. it is used in these videos https://youtube.com/shorts/ECpjj_4lMH4?feature=share

Robert Feranec , 07-28-2024, 03:16 AM

https://youtube.com/shorts/ONvW9_bEJ8Q?feature=share

Robert Feranec , 07-28-2024, 03:16 AM

if it helps, here is schematic

Robert Feranec , 07-28-2024, 03:18 AM

Robert Feranec , 07-28-2024, 03:19 AM

be careful, it is not final schematic, I only created this for fun and for fast test

Robert Feranec , 07-28-2024, 03:20 AM

also by aware, the reason why I never finished this project is, in many devices you need to somehow emulate the event of inserting the SD card so you need to toggle CD (card detect) pin on the device where you are connecting the SD card

Robert Feranec , 07-28-2024, 03:25 AM

theoretically you could access it from two same devices at the same time, but realistically before the communication starts, device will set registers in the SD card and these settings may be different between different devices. So in reality access from multiple devices at the same time may be hard to implement.

Anik , 07-28-2024, 03:26 AM

I understand,

Anik , 07-28-2024, 03:26 AM

I will research more about this

Anik , 08-01-2024, 11:13 AM

@Robert Feranec Sir, I dont need to access same time. Its needed to access memory by switching each other. I have separate them fully also with 3.3V power where every analog channel can handle 100mA power. That means The Memory will also be disconnected everytime from other device. Maybe the register willbe reset?? And it will work??

Robert Feranec , 08-02-2024, 08:03 AM

maybe it will work (i did not fully check your schematic, at the first sight I would at least add decoupling capacitors), I am just interested to know why you don't use the chip I have in my schematic - the chip specifically designed to MUX SD cards? TS3A27518E datasheet specifically says Applications: "SD-SDIO and MMC two-port MUX". I am just curious