Home | Reverse engineering | BTMD v0.1 - v0.2 - v0.3 - v0.4 | References
An incremental improvement over v0.2: adding a small microcontroller circuit to have the Bluetooth module automatically start up once the MD player is turned on, greatly improving the user experience.
- ATtiny13A microcontroller
- 0.14mm² wire, multiple colors
- Resistor, 0805, 1kΩ
- Heatshrink tubing
- Kapton tape
- Double-sided adhesive tape
Flash the microcontroller with the provided firmware. The firmware is extremely simple: Upon power up, the microcontroller sets one of its output pins to HIGH for 3.2 seconds. This is long enough to trigger the Bluetooth module to turn on, but short enough not to trigger pairing mode. Afterwards, the pin is set LOW, and the microcontroller goes into sleep mode indefinitely. This functionality could surely also have been implemented using a small comparator circuit; however, the ATtiny was immediately available at the time, and requires zero supporting circuitry to work, and not even a PCB to sit on!
Attach wires to the microcontroller's leads as per the schematic, with an inline 1kΩ resistor on the output pin PB3 (pin 2).
Remove the plunger on the MD write protect detector switch (S803, "PROTECT DETECT"). This will cause any inserted MD to register as write-protected, regardless of the state of its write-protect tab. Since all hardware for writing to disc has been removed, this behavior is desirable; without this measure, any attempt to record to disc, or to edit the disc's TOC, would leave the device stuck in an endless loop attempting -and failing- to write the data.
(No photo of this step)
Wire the microcontroller as per the schematic. Connect the microcontroller's output pin to the Bluetooth module's button pin, in parallel to the wire coming from the front PCB's End Search button. This way, the button can still be used to pair new devices, or to force the Bluetooth module to turn on and off if needed.
Fix the microcontroller in place with double-sided tape. Cut out gaps in the front casing's internal ribs to route the wires.
Protect everything with Kapton tape and close it back up.
Your BTMD player now has auto-connect on power up functionality! 🎉
- Bluetooth range is rather limited due to the closeness of the antenna to the sheet metal chassis of the MD mechanism.