TapeBuddy64 USB device disconnects when tape drive starts (possible overcurrent)

[jestemkojak]

USB device disconnects when tape drive starts (possible overcurrent)

I have assembled this project, but every time I start the tape drive (play, rewind, etc.), the device disconnects from USB. This appears to be caused by excessive current draw when motor starts.
I managed to read one tape only by starting the tape drive before launching the software. It still disconnected, but was able to restart.

I tested this on two computers and also with different Datasette units, with the same result each time.

On Linux (raspberry), the system reports an “overcurrent warning”, which seems to confirm the power issue. I also tried powering the drive from two USB ports simultaneously, but this did not change the behavior.

Do you have any ideas how this could be fixed or mitigated?

[jestemkojak]

I did some measurements. I think it's a voltage drop on 5V (below 4V) that resets the ch304 and in effect disconnects from usb.

Current spike on motor start (300mA seems reasonable for USB):

Voltage drop on ch340 VCC pin during motor start

[jestemkojak]

Some more observations:
Using a shorter (~30cm) and thicker usb cable mitigated the issue for my c2n unit. However TapeBuddy still disconnected with my noris data Datenrekorder DR1535. I'm adding a PWM-based soft-start feature in #30