SD card on own custom PCB

Hello,

I'm in the process of making a data logger and want to store data on an SD card.

I have used an SD card shield before, however now I am considering making the SD card slot an integrated part of the board rather than adding it in via a shield. Therefore I plan to use a surface mount device SD card slot.

Using a rework station, I plan to solder the SMD SD card slot onto a custom PCB.
From my research it appears that if I am using a 3.3v device (ESP32) then I can connect the pins from the SD card slot, directly to the ESP32 without anything in between? Or do I need to add some form of filtering or current limiting resistors?

Is there a schematic with the recommended hardware for including an SMD SD card slot.

Thank you,
Jock

Yes. If you look at the schematics for 3.3V SD card modules (e.g. Wemos mini shield) the only component other than the SD card adapter is a 0.1uF bypass cap.

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Do you have any other SPI devices on this 'custom PCB' ?

In terms of mechanical strength, this may not work very well. An SD card poses a fairly long arm/lever that can easily break away the card slot from the PCB unless it's very firmly mounted. Generally, hot-plate or reflow-oven soldering work better for this. In a pinch, a regular soldering iron can be used, but how well this works depends a bit on the geometry of the component you select. The one thing that will likely not work well is a hot air rework station, since those generally fail at sufficiently heating up the contacts on such large components.

I have some custom boards which include an SD-card holder. How well they are attached depends on both the holder as well as the footprint used in the PCB design software. I ordered the holders first, then created an exact footprint. The holders in my case also have some lips on the top shield that could easily be soldered with an iron onto the PCB. For the connections to the card i use a hot-air blower (re-work station) And all works really well.

On an ESP32(s) there are 2 SPI busses available, and most pins can be used.

I actually have 10K pullup resistors on MOSI, MISO, SCK & DAT2 as well. Those were also on the shield i used before, and as SMT resistors take up very little space i thought to just add them

No I don't, would I need some other components if that were the case?

ok noted, thanks for the advice.

any idea on the benefit of those pullup resistors?

No.

But on an EPP32, I have not found that the SD card is that reliable when there are other SPI devices on the same bus. I normally arrange to have the SD card on its own SPI bus which is possible on an ESP32.

tbh no idea.

no why ? an esp32 has multiple SPI busses, which will allow the use of more SPI devices actually simultaneously. More SPI devices on the same bus is of course also possible, but then only alternatingly.

Ok great, i'll keep that in mind if I need to use another SPI device on the same line. Thanks!

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