It's an odd one then as the two tests I've done show otherwise.

I've successfully injected +5V on two devices that clearly wouldn't work (and didn't work) on the N810's 100mA supply by disconnecting the internal +5V and Ground and running it through my own battery supply. This includes a larger SD Card reader that wouldn't power with the N810 supply, and a Huwaei HSDPA Modem that was detected fine (dmesg logs said so, but had no drivers installed) - without power injection the modem wasn't detected at all.


Strictly speaking you're right about power negotiation (part of Host Negotiation Protocol) - but I assumed that the host would try to initialize the device when in low power mode, retry negotiation despite there being insufficient power "just in case" there is enough residual power to kick things off - warn you that power is insufficient (draws a lot of current) but maintain the device connection if it can. Kind-of like a fallback.


It may well be down to USB2 sporting the: Battery Charging Specification 1.0: Released in March 2007.

Adds support for dedicated chargers (power supplies with USB connectors), host chargers (USB hosts that can act as chargers) and the No Dead Battery provision which allows devices to temporarily draw 100 mA current after they have been attached. If a USB device is connected to dedicated charger or host charger, maximum current drawn by the device may be as high as 1.5 A. (Note that this document is not distributed with USB 2.0 specification package.)



A lot of these devices "power up" when connected to dedicated PSUs -- my mobile phone for example, the Huwaei modem (blinks and negotiates a 3G connection as LED turns blue), a typical card reader lights green, a portable hard drive spins up. Perhaps when powered up with higher current (as is the case when using Power Injection or your own USB charger) their "power negotiation" protocols in HNP are skipped?


The Application note here: http://www.maxim-ic.com/appnotes.cfm...e_number/1822/ briefly covers OTG and has some interesting info on the type of circuitry involved.


*shrugs* All this is moot now anyway since you're saying there are conflicting reports on what works and what doesn't.





I'd probably go with a solution that a few others have mentioned - a pigtail. But add the right angle option so you could stick it to the back of the N810 and forget it's there.