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Home | Reverse engineering | BTMD v0.1 - v0.2 - v0.3 - v0.4 | References

BTMD v0.1

The first attempt at building a Bluetooth-enabled Minidisc player.

ℹ️ This version is obsolete. However, the v0.2 writeup references a lot of the information on this page, so reading is recommended nevertheless.

Requirements

  • Inspection of the reference materials
  • Electronics and soldering skills
  • Good equipment for soldering and troubleshooting (multimeter, oscilloscope, etc.)
  • Patience and perseverance

⚠️ This is not a beginner project. Even though this document may read like step-by-step instructions, not every detail is covered, and some intuition and skill is required.

Materials

Preparation of Bluetooth module

Open the casing of the Bluetooth transmitter. The approach that worked best was to clamp the casing in a vise to crack it open. The two halves separated rather cleanly.

Desolder the following:

  • Li-Ion battery
  • USB-C jack (USB1)
  • tactile switch (KEY1)
  • LEDs (D1 and D2)
  • the wires going to the 3.5mm audio plugs.

This will significantly reduce the total thickness of the module.

Preparation of Minidisc unit

Remove the back cover to expose the main PCB.

Detach the ribbon cable going to the front PCB, which handles the buttons and LCD screen on the front of the device. Separate the front casing from the MD mechanism. Be careful not to lose the little torsion spring.

Remove the front PCB. Cut both traces going to the End Search tactile switch (top right, next to the LCD), and expose a bit of the traces (on the side of the cut going to the switch). Solder wires to the exposed traces. The End Search switch will act as the power and pairing button for the Bluetooth module.

ℹ️ See the reverse engineering page to read more about how this button was chosen.

Remove the magnetic write head from the MD mechanism, as well as the little bracket holding it in place. This is necessary since otherwise these parts will collide with the Bluetooth module once everything is assembled.

⚠️ This obviously means that the MD unit is no longer a recorder, but only a player. A small price to pay for wireless glory! See the references for ways to easily load music onto Minidisc.

Wiring and integration

Mount the Bluetooth module and the voltage regulator module on the inside of the front plasic casing with double-sided tape. Wire everything up as per the schematic. Use Kapton tape to protect the PCBs against short circuits (especially to the sheet metal chassis of the MD drive unit), and to secure the wiring in place.

ℹ️ Use the service manual linked to on the references page to identify the necessary components and test points.

on MD unit on BT module
Power + IC901 pin 40 BAT+
- C314 cathode BAT-
Audio L TP101 L_IN
R TP201 R_IN
GND TP319 GND
Button 1 End Search (1) BAT+ via 10kΩ resistor
2 End Search (2) KEY1

Close everything back up. Enjoy!

And then realize everything you could have done better, and proceed with v0.2.

Known issues

  • Audible interference from Bluetooth module in transmitted audio (→ v0.2)
  • Status of Bluetooth module not visible from outside (powered? connected? pairing?) (→ v0.2)
  • Bluetooth module has to be turned on separately (additional button press) (→ v0.3)
  • Attempting to record onto disc or edit the TOC causes device to hang (since it cannot write to disc) (→ v0.3)
  • Bluetooth range is rather limited due to the closeness of the antenna to the sheet metal chassis of the MD mechanism.