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My phone (Motorola DROID RAZR MAXX) seems to have problems accepting touch input when connected to a non-OEM power source. When connected to my computer via USB, it accepts input fine, as it does when connected to an Xbox 360 through USB. When connected to the wall USB charger it shipped with, it also accepts input fine, but when connected to a third-party wall USB charger, the touch input goes crazy and starts selecting objects all over the screen where I'm not pressing. The charger did not do this with my previous Android phone.

Is this because there is some data connection it is looking for through USB so that it acts weirdly if not using an OEM charger or actually connected to a data-using device?

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    Let me guess: that 3rd party charger comes from HTC? In that case I can confirm the strange behavior to 100%. To me it seems they have some special PIN assignment which confuses Motorola devices (providing a strange signal on some additional PIN I'd guess). Some proof of my theory: XDA
    – Izzy ♦
    Feb 11, 2013 at 20:57
  • See also: PinOuts, note the "x" PIN which may be connected to GND for cable detection in some cases. If the Droid expects it one way, but the cable does it the other way, this might cause some confusion. In my case with the HTC cable, the "x" PIN seems to be grounded on the charger side (power connector; here the cable is connected with standard USB) -- as when I use the same cable with some other power connector, it works fine.
    – Izzy ♦
    Feb 11, 2013 at 21:06
  • @Izzy - yes, it does come from HTC.
    – SSumner
    Feb 12, 2013 at 0:57
  • Thanks for the confirmation! In that case, I convert my comments into an answer (see below). As stated, though Ales's EMI theory has its points, I agree with you that "my" theory is more likely to hit the point. But there was no scientific study on that (or all of us missed it) -- so I could be wrong as well ;)
    – Izzy ♦
    Feb 12, 2013 at 7:23

2 Answers 2

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Though Alex's answer has its point; but as the OP confirmed the second adapter in question is a HTC charger, I hold it more likely that a special "PIN usage" is the cause. As I explained in my comments to the question:

PinOuts describes how the PINs of the USB connector are used in general.

USB PinOuts screenshot from PinOuts.ru

Note the "x" PIN which, according to the description, may be connected to GND.

Now to my observation: As I was annoyed by the very same problem, I decided to dig a little deeper. I tried 3 different cables with the HTC power unit versus two other power units (one Motorola, one generic) on my Motorola Milestone 2. In short, all cables behaved exactly the same: connected to the HTC power supply, they caused the very same behaviour described in the question, i.e. unpredictable reactions to the touchscreen. Connected to any of the other power sources, there was no such effect. So the cause very clearly was the HTC power supply.

If EMI were involved, as Alex suggests, the same strange behaviour should appear here daily, as that HTC power supply is connected to a power source (and such must emmit those electro-magnetic disturbance), and my devices are often positioned not much more than 20cm from it. A connected cable might bundle that, true -- but I still hold my theory for more likely. And as one can find by looking at this XDA thread, HTC chargers do obviously use a different PIN layout -- which adds its weight to my arguments.

Besides: Other devices connected to the HTC charger (I tried with two tablets, none of them a HTC) did not show the effect. So with the EMI argument, the resumé would not be "HTC builds lousy adapters", but "Motorola builds lousy displays" ;)

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The effect you are observing has nothing to do with any "strange signals" like some suggested but with the quality of the power adapter. Capacitive touch screens are very sensitive to EMI and the low quality power adapter you are trying to use is interfering with the touch sensor controller in the phone.

Slightly more detailed description of the problem

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  • I don't think it's low quality - I think Izzy's comments is the reason. It's a HTC adapter.
    – SSumner
    Feb 12, 2013 at 0:57
  • It only proves that HTC makes crappy adapters. There's no "signal" on the ID pin of USB connector. Period. If there's an EMI noise - it's because of poor design and/or low quality.
    – user23414
    Feb 12, 2013 at 5:31
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    Or it proves that HTC makes better displays (not that sensitive to EMI, but as sensitive to touch as others) -- as the problem seems not to appear on HTC devices used with the very same adapter? How likely is that.
    – Izzy ♦
    Feb 12, 2013 at 7:03
  • Well, but the article linked may suggest a third variant: Do all Motorola devices use such a crappy touch screen controller as described there for the Photon and Atrix? Especially the Droid Razr Maxx (from the OP) and the Motorola Milestone 2 (mine)? That would explain why my tablets were not affected, provided they use a better controller. So I must admit, Alex made his point (@Alex: you just forgot to point out the crappy controller mentioned on the linked site. My apologies for not checking your provided source thoroughly enough before!) Will check that and come back then.
    – Izzy ♦
    Feb 12, 2013 at 15:20
  • A deeper look shows: what that site mentions as the worst touch screen controller is, according to their link, the Atmel mXT224. Look for it: [it] is undoubtedly one of the most popular ones as evidenced by a number of design wins (followed by a list of devices, including 3 Motorola, 3 HTC, and 10 Samsung devices (Galaxy S, Galaxy Tab, Nexus S amongst them)).
    – Izzy ♦
    Feb 12, 2013 at 15:36

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