Thanks for the information in this thread, it worked....then after about 2 weeks 24x7 usage, I had a crash on my Orange Pi One (not related to USB functionality I don't think, the system was probably doing a database import at the time). After this, the OTG port didn't seem to work any more in host mode. I tracked it down to not being any internal power on the the port, the USB data lines were OK. Examining the board schematic shows the power for the OTG port comes through 'U11' which in turn is controlled by a line from the H3 chip, but as my board didn't have U11 on the silkscreen I didn't get much further than that. I assumed I'd blown up that part of the board as nothing seemed to fix it and the rest of the system continued to work flawlessly after a reboot. That was not the case however, as a complete reinstall (Armbian stretch) from scratch and hey presto, the internal USB power is restored. In case it happens again, anyone have any idea how to troubleshoot powering of the OTG port in USB host mode when/if it goes wrong?