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Topic: USB OTG's Resistance between the ID and Gnd Contacts (Read 469 times) previous topic - next topic

card5

Hi all


I read in the past, that for a USB plug to be identifiable as "OTG", it has to have 5 contacts instead of 4,
(e.g. USB Micro),
and the ID and Gnd contacts in that usb plug should be connected with a Resistor, with some specific resistance.
This resistance indicates that this side of the cable, is OTG.

A non-OTG cable, will have both sides (plugs) of it without any resistor on the ID and Gnd contacts,
meaning complete disconnection.



So,
I decided to measure using a Multimeter, the resistance of the ID+Gnd contacts in all the Micro USB cables that I have
(that's 8 cables).
2 of these cables a should be OTG, since that's what it said when I bought them,
and the other 6 cables should not be OTG, or at least no-one specified that they are.


Here are the results:

The 2 cables that are supposed to be OTG, showed a connection bewteen the ID and Gnd contacts.
Not a resistance, but complete connection.

Out of the 6 cables that should be regular (non-OTG),
5 cables showed complete disconnection between the ID and Gnd contacts,
and 1 of the 6 showed a special result of 198.8KΩ resistance between ID and Gnd.
I assume you can call this 198.8KΩ a 200KΩ resistance, with a 1% deviation range for the resistor..


And so the 2 questions that arise from this short experiment are:

1) The Real OTG cables showed 0Ω connection,
   shouldn't that be some resistance and not 0Ω?

2) The non-OTG cables showed complete disconnection, like the should,
   but 1 of the 6 showed 200KΩ resistance, so what does this 200KΩ mean?
   Is there maybe some webpage with list of resistances between the ID and Gnd contacts, to know what each resistance mean?



Thank you all

mazur888

#1
Sep 03, 2019, 11:09 pm Last Edit: Sep 03, 2019, 11:12 pm by mazur888
yeah, in standard otg to use as usb ID pin is connected directly to GND that's why you are getting 0 Ohms. This mode is to use mouse, keyboard, camera, flash drive etc..

also different accesories use different resistance between ID and GND so phone can recognize what is connected straight away.
For example I was using i think 330R or 330K resistor (can't mind now)  for samsung phones, it was far quicker to put phone in to firmware flashing mode.

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