As one of the early adopters of Arduboy I’ve enjoyed seeing the excitement around the creation of the mod chip. I even (with help from the community) managed my own epic repair.
While I could hop on the current flash mod buy - I sorta want to roll my own. Having an arduboy with a bundle of wires shoved into it scratches an itch of ‘make it mine’.
I know that the two chips are the W25Q128 & ATtiny85 - finding versions of these on digikey is easy enough, and I’m fairly confident I can find ones that will work. What isn’t clear in my searching around is the circuit layout. The flex circuit is two sided so it’s tough to figure out from an image. I’m sure @bateske has posted the actual schematic somewhere - but there are many revisions. If I’m going the DIY route - I’d really like to create a work-alike to avoid other issues.
The attiny85 is only necessary to reflash the bootloader onto the atmega32u4. If you have a usb icsp programmer (usbasp or even another arduino programmed with the arduino as isp program) you can just manually do this once and then it’s set.
The capacitor is just for bypass/decoupling to guard against possible power signal induced electrical noise. The resistor is to ensure the flash chip is disabled when the SDA pin is in it’s default state as an input. I’m not sure if @bateske included either of them on the production FX, as I’ve never seen a schematic for it.
As @sjm4306 said, you’ll need an ICSP (In Circuit Serial Programmer) to burn a new bootloader into the Arduboy to support the flash chip (which was the only job of the ATtiny85). If you don’t have one, then with proper wiring you can use either your second Arduboy or your dev kit as an ICSP.
The attiny85 (or attiny45) is used to conveniently program the bootloader and to keep the SDA pin high using internal pullup.
Adding the attiny will allow you to program the bootloader through the activator sketch or by pressing reset for 2 seconds (after attiny has been programmed) This last feature dubs as a restore feature in case the bootloader was corrupted.
However the attiny is not required to make use of the flash chip. The official Arduboy FX does’nt has an attiny85.
Without the attiny85 a 10K resistor needs to be connected to the flash chip select to ensure no ‘random’ data is written to the flash chip during special cases like start-up, programming the bootloader, non fx aware sketches.
The cap wasn’t added. The pull-up resistor was. It sits just right from the charging LED resistor.
As mentioned, the pain is hooking up a programmer and then running all the python scripts. For someone who is used to doing such things it’s very simple. But for users who programming and soldering is still new to them that’s why the FX is a great option.