Flexcable twl

DSi modchip PCB and flex-cable

[!IMPORTANT] This PCB is still a work-in-progress and has bugs.

This repository contains the KiCAD design files for the DSi modchip and the cable flex-PCB.

Notes

Currently, you'll have to order and make these yourself. I don't think making them widely available already is a good idea, there's still a few bugs left in the design.

The issues with the modchip PCB itself are listed here. Additionally, inserting a cable into the modchips USB socket too forcefully can cause the modchip PCB to snap in half, which is bad.

I haven't actually gotten the flex-cable to work properly. There are problems with either a too large parasitic capacitance on the glitch signal line, or bad contacts between the flexPCB and the glitching MOSFET. I suggest deadbugging the crowbar MOSFET instead, if that's something you're capable of.

Ordering/fab instructions

The modchip is a 4-layer board that should be 0.8 mm thick. I've gotten it fabbed successfully from both Aisler (at 1.6mm thickness) and JLCPCB.

The flex-cable consists of two layers, needs stiffner in certain places, and has been fabbed from JLCPCB.

Bill of Materials

Modchip main components

These are all the components required for the core functionality of the modchip.

[!NOTE] J5 is optional, and is only needed when you use the flex-cable. It can be omitted when deadbugging the crowbar MOSFET.

[!TIP]

• For Q4, several compatible components exist: Diodes DMC{2710U,3400S,3401L}DW, Toshiba SSM6L35FU.
• For SW1 and SW2, you can use one of the following:
  • C&K {RKB,PTS81[05]}2SJ[GKM]250SMTR LF
  • Alps Alpine SKRPABE010
  • E-Switch TL3365AF180QG
  • CUI TS20-42-25-WT-160-SMT-TR
  • Wurth 434123025826 or 434133025816
• For U1, you could try using the RP2350A once its erratum E9 has been fixed in hardware.
• For U2 and U4, any similarly-sized 3.3V >100MHz QSPI flash chip should work. Requirements on U4 are lower (only 1-bit SPI, 16 MHz) but it's often cheaper to buy the same chip in bulk.
• For Y2, try e.g. ECS-120-18-33 or ABM8(G)-12.000MHZ-18

Modchip optional: USB connector

[!IMPORTANT] You most likely want this, though technically everything can be done using an SWD debugger instead.

[!IMPORTANT] Use only one of U3 or U7, never both!

Modchip optional: LED

It indicates the status, except it doesn't work because there's no proper 5V rail available when plugged into the DSi.

Modchip optional: WiFi module carrier

With a few extra components, you can make the modchip act as a real interposer PCB between the DSi motherboard and the WiFi module.

[!NOTE] Only short JP1 if you intend to talk to the WiFi module in a standalone (i.e. non-interposer) manner.

[!TIP] Instead of a MIC5317, many other SOT-23-5 LDOs such as the MIC5504-1.8YM5 can be used instead. I tend to pick ones with a low quiescent current. Do pay attention to the pinout, though, as it sometimes changes even between SOT-23-5 parts of the same vendor.

Modchip optional: I2C level shifter

This can be a neat extra if you want to talk to the DSi's I2C bus. This was used during modchip development, but isn't required at runtime.

[!TIP] Instead of a PCA9306 (from either TI or NXP), an LSF0102 (from TI or Nexperia) or Nexperia NCA9306 can be used as well.

Flex-cable

The flex-cable only needs a single IRFHS8342PbF as crowbar MOSFET. There's also a footprint for a small 0402 series resistance at the gate (e.g. 200 Ohm), but it can be shorted.

Installing the modchip, flashing firmware and payload

See the guide.

License

CERN OHL-S v2