Formal Errata Sheet Style

CEREBEL USB MIDI HOST – Identified Design Errors

1. MCU Clock Frequency: The MCU operates at 8 MHz, whereas the required frequency is 16 MHz.

2. Incorrect MIDI Output Circuit:

   • MIDI Pin 4 is connected to +5 V through a 220 Ω resistor.

   • MIDI Pin 5 is connected to 3.3 V through a 220 Ω resistor.
     This configuration is invalid because:
     a. A 5 V pull-up on Pin 4 cannot be combined with a 3.3 V signal on Pin 5.
     b. Both voltages must be equal to ensure proper operation of the receiving MIDI device.
     Otherwise, the optocoupler LED will remain continuously active (anode at 5 V, cathode at 3.3 V).

Recommended Corrections (by R. Meurer, midisoft.de):

1. Replace the MCU with a 16 MHz / 3.3 V version, or alternatively use a 16 MHz / 5 V MCU together with a 3.3 V voltage regulator.

2. Isolate MIDI Pin 4 and insert a 33 Ω resistor between MIDI Pin 4 and 3.3 V.

3. Replace the series resistor on MIDI Pin 5: change from 220 Ω to 10 Ω.

4. Update the device with the latest firmware (USB MIDI HOST by Yuuichi Akagawato).

Community Hardware Fix Guide Style

CEREBEL USB MIDI HOST – Hardware Issues & Fixes

Problems

1. The MCU runs at only 8 MHz — it should be 16 MHz.

2. MIDI OUT is wired incorrectly:

   • Pin 4 has +5 V via 220 Ω.

   • Pin 5 has 3.3 V via 220 Ω.
     This mix of 5 V and 3.3 V doesn’t work. Both lines must be at the same voltage, otherwise the optocoupler in the receiving device is always on (5 V on anode, 3.3 V on cathode).

Fixes (by R. Meurer, midisoft.de)

1. Use a 16 MHz / 3.3 V MCU. Alternatively, use a 16 MHz / 5 V MCU and swap the regulator to 3.3 V.

2. Cut the trace to Pin 4 and add a 33 Ω resistor between Pin 4 and 3.3 V.

3. Change the resistor on Pin 5 from 220 Ω to 10 Ω.

4. Flash the latest firmware (USB MIDI HOST by Yuuichi Akagawato).