FreeDMO

Endless freedom for D.MO 550 series label writer printer.

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Wiring

Components needed:

• 1 × STM32F103 bluepill
  search for: STM32F103 bluepill / STM32F103 bluepill with STLinkV2
  ::ATTENTION:: Make sure your blue pill is using the correct STM32F103C8T6. Some places sell blue pills with STM32F103C6T6 which are not compatible.

• 2 × cable
  search for: 6 pin 1.25 mm / 6pin 1.25mm Wire To Board Connector / JST GH 6pin

• 2 × resistor 4.7kΩ

• 1 x USB UART -> TTL cable for uploading the firmware and some jumper cables for easy connection of the ground https://www.amazon.com.au/dp/B08761Z5K9

Install Tips:

1. Buy a USB UART -> TTL cable at the start of the project and upload the firmware before you start all the other steps. https://www.amazon.com.au/dp/B08761Z5K9
2. For firmware flashing you don't seem to be able to use the MicroUSB to upload it. You need to use the standard procedure and solder/jumper a USB UART interface or cable onto the BluePill. You don't need to connect all 4 pins to the board (you can but keep in mind one of them is used by later steps so you may have to solder). You only need to connect the TX, RX and ground wires because you can power it via the MicroUSB port - just plug that into a normal MicroUSB charger. But keep in mind the ground wire can just be jumpered onto the 4-pin ground wire sticking out the end of the blue pill temporarily whilst you are flashing the firmware. No real need to solder on a pin for the ground.
3. Check the colours on your JST GH 6pin cables are the same as the author. Mine were different hence nothing worked (cables purchased online seem to have different colour orders). I had to disconnect and swap the green and white wires, as mine were backwards compared to the ones the author used. You can use a needle and carefully disconnect the pins and change the order under a magnifying glass. You probably have one in your soldering station if you are soldering these tiny boards anyway. Once I did that, it all worked perfectly.

TROUBLESHOOTING NOTES:

• If you turn the printer on and insert paper, feed it and advance it to the first stop, and you get an error, then the main board is not connected to the JST GH 6pin cable (i.e. blue pill and RFID aren't connected).
• If you turn the printer on and it's not detecting any labels, you do the above, and it's still not detecting anything, then you have a dry solder somewhere on the blue pill (inspect them all with a magnifying glass), or one of the JST GH 6pin cables is not seated properly.
• When it works, you should see your printer detect your labels per whatever firmware options you selected (even if there's none in the printer). And when you print some, and then restart the printer, the count will reset to full. i.e. start at 120, print a label - now 119, restart it goes back to 120.

Assembly

→ Make sure that the cables are connected correctly.
The left cable goes to the RFID board, the right cable goes to the main board of the label printer.

Attaching the RFID board is optional. If you only want to emulate one specific label type you don't have to connect the RFID board and 2 x 4k7Ω resistors.

STM32F103 blue pill:

Connection to RFID board:

Connection to main board:

Firmware

Option 1: Install the required ARM toolchain from distribution

• install the ARM toolchain from distribution (e.g. on Debian-based GNU/Linux install the gcc-arm-none-eabi and libnewlib-arm-none-eabi packages)

• run make to compile the firmware

Option 2: Install required ARM toolchain GNU Arm Embedded Toolchain from ARM:

• download and unpack from here: https://developer.arm.com/tools-and-software/open-source-software/developer-tools/gnu-toolchain/gnu-rm/downloads

• open the Makefile and modify the first line GCC_PATH to point to the GNU ARM embedded toolchain bin folder
  e.g. GCC_PATH = ../gcc-arm-none-eabi-10.3-2021.07

• run make to compile the firmware

Option 3: Use the precompiled firmware

• a precompiled firmware binaries are available here: Download

  You can choose one of the firmwares which has a default SKU for emulation (used when no real RFID tag is present)

Download the firmware to the STM32F103 bluepill board

• after compilation you can find the firmware file freedmo.bin in the build folder

• you can write the firmware via

  • SWD download using JLink-V2 and ST's JLink-Utility

  or

  • Serial download using an UART adapter and ST's FlashLoader Demonstrator
    This is the same procedure as downloading an USB bootloader to the bluepill board:
    https://www.electronicshub.org/how-to-upload-stm32f103c8t6-usb-bootloader
    Just select the file freedmo.bin in "Download from file" (2)

STM32CubeMx

The project comes with the CubeMX .ioc file which can be used to modify pins and/or change to different CPU types. The complete code is inside of ST's magic BEGIN_USER_CODE / END_USER_CODE markers so "Generate Code" in CubeMX can be used without any problems.

STM32F103 pin assignment

D.MO RFID tag emulation

After startup of the printer a default tag emulation is used which can be defined in the firmware. The emulation will count down correctly until the end of the roll is reached. A power cycle / sleep+wakeup of the printer is enough to reset the emulated tag counter back to it's maximum.

If the original RFID board is also connected and a spool with D.MO RFID tag is found then the emulation data is updated with the data from this RFID tag. Just the counter will be emulated in this case. This enables the use of any D.MO format unless you have at least one original spool (you can peel the RFID label of that role and attach it to the inside of the printer).

Please consider dumping this data and providing it here for others (see: https://github.com/free-dmo/free-dmo-tag-dump).

D.MO uses it's own Originality Signature (own signing key) which is used to sign the UID of the tag. This is used to only allow D.MO's own SLIX2 tags. However when you can emulate the UID you also can emulate the corresponding signature bytes, you just need to dump them from a valid tag.
(see: https://github.com/free-dmo/free-dmo-tag-dump).

The firmware contains some D.MO SLIX2 tag dumps which you can choose from:
file: Src/main.c

#define SLIX2_TAG_EMU 1
//#define SLIX2_TAG_EMU 2
//#define SLIX2_TAG_EMU 3

It does not matter which TAG_EMU you use. All of them will work for now. Maybe... in future D.MO will release new printer / firmware which might block those UIDs... but then we only need to dump a new spool of labels to get a new and valid UID+signature.

The data about the labels (SKU, size, count, ...) is encoded in the standard SLIX2 data blocks. Inside of this data is no dependency to the UID or signature. This enables a "mix and match" of SLIX2 tag (UID+signature) and the media data used from the printer. Unfortunately the encoded data uses an unknown CRC32 algorithm which limits us to use existing dumped label formats only.

You can choose from the list of included label data by selecting the SKU:
file: Src/main.c

#define DMO_SKU_S0722430 // 54 x 101 mm, 220 pcs.
//#define DMO_SKU_S0722550 // 19 x  51 mm, 500 pcs.
//#define DMO_SKU_S0722400 // 36 x  89 mm, 50 pcs.

Happy printing... 😈