I've a device (An old NES cart, actually) that I've fitted with a USB port and a flash drive. I'm using it in a NES to Raspberry Pi conversion. My idea was to have a port on the side for connecting to the computer to upload data (movies, ROMs, music, etc.) and use the original 72 pin connector to connect to the Pi (using the original slot loader from the NES).

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Obviously 5v and Ground are soldered in parallel.

When I soldered up the USB port (basically just a USB extension cable), it works fine. However, when I add the data wires to open pins on the connector, the drive ceases to function.

I have no idea why this is happening. Any clues?

  • \$\begingroup\$ You want to have to usb connections from one flash drive, and not to use at the same time right? \$\endgroup\$
    – Passerby
    Mar 17, 2015 at 23:58
  • \$\begingroup\$ Yup. Only one will be used at any given time. \$\endgroup\$
    – watswat5
    Mar 18, 2015 at 1:58

1 Answer 1


USB uses very fast signals (480 Mbits/sec at high speed) to transmit data serially. As such, it is very sensitive to transmission-line effects in the cabling. What you have done is created a "stub" connection (whichever host port isn't being used at the moment) that really messes up the data signal because of the signal reflections from both the point where the three sets of wires are joined, as well as the open end of the stub.

Bottom line is, you simply can't do that. You might be able to install a physical DPDT switch to switch between the two host connections, but even that would be questionable.

  • \$\begingroup\$ I Finally got it to work. Stress tested it on both the USB port and 72 pin connector by copying 1000 files over and back and calculating the md5 for each. For some reason, soldering one wire to 2 separate pins (more reliable) wouldn't work, but having only one pin worked like a charm. \$\endgroup\$
    – watswat5
    Mar 18, 2015 at 21:33

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