[chbot] 9.6" tablet for < NZ$300

[Charles Manning]

I've been working a lot with USB devices plugged into Android phones and
tablets in the last 18 months or so.

All the phones & tablets I've worked with (many) have been able to power
the devices that I have been plugging into them (up to 250mA or so) and
almost all (ore or two exceptions) have enumerated devices up to 500mA,
however there are some caveats:

1) It certainly does drain batteries quicker.
2) Be very careful about plugging in devices that draw more current than
they enumerate for. I made a stuff up in one release of fw where the device
said it wanted up to 200mA, but then drew 230mA for about 1 second during
initialisation and then dropped to under 100mA.That was enough to damage
the port.  Make sure the current stays below 100mA until enumeration is
complete. Three of the same tablets (Samsungs IIRC) blew their USB ports
and would no longer drive USB devices.
3) Type C connectors are getting popular. They are problematic. Type C OTG
adapters are very iffy. Get Micro AB connectors if you can.




On Mon, Aug 28, 2017 at 6:37 PM, Geoff <sdfgeoff at gmail.com> wrote:

> Be aware that most tablets cannot provide much power over OTG. They can
> provide enough to power a USB drive, and some can power a mouse. But when I
> tried to power a atmega32u2 development board via OTG, it was very
> dependent on the tablet make/model as to whether it could manage.
>
> Stackexchange
> <https://electronics.stackexchange.com/questions/181500/how-much-current-can-an-android-phones-usb-port-supply>
> says:
>
>> The OTG spec calls for at least 8mA and allows negotiation for higher
>> currents if the peripheral needs more power. OTG devices can provide up to
>> 500mA, but in realistic terms, handheld portable electronics don't have
>> 500mA to spare for external loads. 100mA is a commonly accepted realistic
>> maximum.
>
>
> So you may want to check with people who actually have the tablet you wish
> to buy.
>
> G
>
> On Mon, Aug 28, 2017 at 8:21 AM, Mark Atherton <markaren1 at xtra.co.nz>
> wrote:
>
>> Hi All,
>>
>> I have been looking around for a 10" tablet for a while and the Samsung
>> SM-T560 is currently on sale.
>>
>> Unit has quad core 1.3Ghz CPU, 1.5GB RAM, 8GB internal FLASH, uSD card
>> slot, but more to the point has WiFi and USB OTG - OTG being the deal-maker
>> here. Also running Android 4.4 which is getting on a bit.
>>
>> Main interest is Web surfing, video playback, and control of some
>> external home-cooked hardware via OTG (and associated 5V power).
>>
>> One test report claimed almost 9hrs of continuous video playback on a
>> single charge which is quite respectable.
>>
>> http://www.gsmarena.com/samsung_galaxy_tab_e_9_6-7295.php
>>
>> Is anyone aware of a significantly better value-for-money product in the
>> sub-$300 range (since I am picking it up, this includes GST, and $0
>> shipping).
>>
>> Thanks, Mark
>>
>>
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