Truely a smart phone

When I plug in my cell phone, how does it know that the power cord I used isn’t the one that came with the phone?

I use four different power cords with mine, purchased from a variety of sources. My phone has never mentioned anything to me about caring one way or another…it just seems grateful for the electricity.

Wrong voltage in.

Power cord? How old is this phone? I thought all cell phones had to either be mini-USB or whatever Apple’s cord is called.

I think it’s just sensing out of spec voltage, as I’ve plugged non-Motorola chargers with mini USB ends on them into my phone and gotten an “Unauthorized Charger!” message.

Munch- I’ve not heard of such a spec, but it would be nice. At my office, we have phones that take mini USB, some sort of micro USB, something that resembles a half-size Apple dock plug, and the old-style round plugs as well. Off the top of my head, I want to say the USB variants are for Motorola phones, the small dock plug is from a Samsung and the round plugs are Nokia.

It’s an EU standard now to use micro-USB for smartphones.

For some reason it’s apparently also standard to short the data pins together, which is why my X10 won’t charge from any of the car chargers I have. (But would if I could get myself together enough to solder a resistor in there).

It’ll work with any microUSB cable though.

Apple biases the data pins to specific voltage levels on their chargers. It let’s the attached device know if the charger can supply the required current.

That sounds about right. Then you’ve got HTC, who complicate things still further by fitting standard micro-USB ports to some of their phones and proprietary shapes to others. :smack:

Yes, my new iPhone with the old monster FM Modulator indicates “this phone will not charge with this unit”, bt it will do FM broadcast. Either voltage levels, or looking for some indication on the pins that it’s compatible.

It’s not just Apple. My last phone was a Motorola, and complained about having a microUSB plugged into it that wasn’t the one that came with it.

HTC Incredible… Micro USB I think. So it senses different voltage levels on certain pins? I also think the phone charges a little slower depending on which power cord I use (original cord, car charger or other manufacturer’s cord).

I think there’s some communication between the device and charger: It’s not specific to Apple, I think it’s part of the USB spec. So if the charger only supplies 5 V but no communication, the phone won’t charge properly.

If I’ve followed the topic in phone forums correctly : shorting pin 2 & 3 tells a Samsung phone a (Samsung) mains charger is connected. I haven’t tried it though. It would work on other types as well.

On standards: my girlfriends new phone has micro USB, but you can’t use that to charge the phone. It would have been too simple, I guess. Instead you need Nokia’s own small pin charger thingy.

It’s all rather proprietary. Without getting into many technical details, different manufacturers pick different ways of detecting valid chargers. Some will accept anything that provides 5V on Vusb.
(It’s really bad form to make something that mates with a mini or micro USB connector, but provides more than 5V on Vusb. In my experience, most manufacturers honor this convention.)

Some will check the data pins. Some will check for a resistive load on an ID pin. Some use other methods.


About a year ago, an entertaining article about reverse engineering the iPhone charging cable made the rounds. It’s still a fun read that explains how USB charging works and how the various Apple devices have played around with that standard over the years (and even a bit about why they might want to).

I know just about nothing about electricity; but fortunately, it’s a fairly non-technical article (circuit diagrams not withstanding) so it’s still an enjoyable read. (It doesn’t cover
non-Apple devices which undoubtedly use their own brands of trickery.)

Cool! That might explain why my friend’s Teac clock radio, with iPod socket, stubbornly refuses to charge my iPhone 4.

:: starts wanting to have a soldering iron in my hands once again ::