The cheapest Micro SD card interface in the world

a micro-sd adapter with 7 0.1"-pitch header pins  soldered onto its contacts
micro-SD adapter + pins + solder = working SD interface

It’s only a serial SPI interface, but you can’t beat the price. It should only be used with 3.3 V micro-controllers like the Raspberry Pi Pico, since micro-SD cards don’t like 5 V directly at all.

You might want to pre-tin the pins and apply some extra flux on both surfaces, because these pads are thin and you don’t want to melt them. I used my standard SnAgCu lead-free solder without trouble, though.

label sticker image for 7 pins, from left to right DO, GND, CLK, 3V3, GND, DI, CS
got a label maker? This label’s the same length as an SD card is wide, as shown above.
Made entirely with netpbm

You only need to use one of the Ground connections for the card to work.

big trouble in little microSD

It was a bit of a fight to get the SparkFun microSD Shield working. At first, I thought it was my choice of cards. Then, on reading the manual (ahem), I discovered the section “I downloaded a FAT library for Arduino on my own from the Web but it’s not working! Why not?“. It seems that the SparkFun shield uses non-standard pins for signalling, which they consider a feature, but some consider a bug.

After fixing the code in the awesome sdfatlib library, I’ve now got it logging the temperature of a cooling container of hot water:

You might just be able to make out the LM35 pressed up against the measuring cup.

I remember making a right mess of this experiment in my school final Physics practical exam. I also used to do this in my first job when bored testing Campbell CR10 dataloggers, making a nice 1-d cooling curve with a thermocouple and a cup of hot water.

I think the heating came on a couple of times, as there shouldn’t be bumps in the curve. Here’s the data.