Introdution

These are many open source and commercial about wifi sdcard out there. But it is too expensive, around $100, i dont try it yet, but i think it have much advantage like size, performance... Some diy cheaper, but the design have a common problem which they dont solve it yet.

As we known, to comminicate with sdcard device (diy product), we using 4 wires SPI line, so the writer must be Master and SD Card is slave, now we inject another Master to write Slave sd card, so we must solve problem multiple Master parallel write a sdcard. it may cause incorrect or event short circuit.

With several schematics i found out there, they use a pin to determine what ever sdcard are used by another master so the software will decide write to it or not. Even i hear the expensive having this problem too. But the problem still exists, what happen when we are writing to the card, the old master also doing same action ? Some time i saw these is a seller selling only an extend tf-card cable with $3, so why dont we make one by our self ?

My schematic design is almost same above but the key diffrence is the communication line between each master will be isolate, by the default startup, our esp8266 do nothing, and sdcard action as same as normal sdcard. when the esp8266 retrive command to read write sdcard, we can choose to detect another sdcard using it or interupt other master to capture permission to control sdcard.

In this tutorial you will learn about a ic multiplexer, demultiplexer 74HC4052, ofcouse there are many multiplexer, demultiplexer out these, but this ic suit for out project. It can be using as an analog switch. So the idea of project is: default sdcard will connect to the SPI1 line, so the Master1 can write/read it, when we want use esp8266 we will switch to SPI2 line so SPI1 will be float, it is safe enounght, huh ?

This project assume you aready have basic knownedge and programing several times with the esp8266, i will only explain about ciruit and 74HC4052.

Schematic explain:

comming soon

Software:

This project is base on ESP3D project (ref_1) but it is design to control 3d printer too, im only need sdcard feature, so i disable most of them, and modify UI to to manage upload/ delete files on the sd card. there are very limit pin on the esp8266 can be used, and i need a pin to control the led so im disabled feature to detect there is another master read/writing to sdcard. You should DIY your code to check that in your project.

NOTE:

• This board use most SMD items, althrought i try my best to make it smaller but it still big =)), though, im chosed big SMD items, so you can free practice your solder skills.
• You cannot CNC this board with the hobby machine, sadly :D
• If you order this board from pcbway, please choose board thickness 1mm, it will fit to sdcard slot.

References:

• ref_1: https://github.com/luc-github/ESP3D