Arduino Host USB Shield drives SPI MISO permanently

[KimSJ]

The current rev 2 Arduino Host USB Shield circuit has IC3, which buffers MISO, permanently enabled so that the line is always driven. This prevents the shield being used with any other SPI devices on that bus.

The solution is trivial: connect IC3 pin 1 (nOE) to the D10/SS signal (e.g. IC8 pin 2), instead of to GND. This is an urgent fix; it could and should be implemented immediately as a production patch/rework until the current board layout is revised!

Note: For owners of existing boards, if you have access to surface mount rework, you can easily unsolder IC3 and isolate Pin 1 (the track to GND is under the IC), then refit the IC and add a link to IC8 pin 2. If you don't have such facilities, lifting the IC may be hard. A hack which will probably work would be to cut the track from IC3 pin 4 to the SPI connector pin 1, and insert a 2k2 resistor. (This will not work if you want to have two or more Host USB cards, or course.)