Here’s a new chip from FTDI which brings a nice little feature to the USB-to-serial converter family: charging detection. That means that it is capable of detecting when a battery charger is connected. What does that actually mean? The top of the datasheet gives you the short version, but let’s look at the investigation [Baoshi] undertook to test the full extent of this particular feature. We agree with him that the listed capability leaves those in the know with a lot of questions:
USB Battery Charger Detection. Allows for USB peripheral devices to detect the presence of a higher power source to enable improved charging.
Obviously the chip will be able to tell when a charger is connected, alerting the device when it’s time to start lapping up the extra milliamps. But what type of chargers will actually trigger the detection circuit? After rigging up the test circuit shown above he ran through several scenarios: connected directly to the PC USB port, via externally powered and non-powered USB hubs, and with multiple wall wart chargers. Full results of the tests are included in the post linked above.
[via Dangerous Prototypes]
For enumeration for USB 2.0, your device would have a 1.5K pull up
resistor on one of the data lines.
Dumb charger: D+ & D- shorted, so D+ and D- lines are logic level high
because of the 1.5K pullup
Apple charger: D+ & D- are 2V or 2.8V which are LVTTL high. (*)
So if you could read the logic levels of D+ and D-, you can identify
whether or not you are connected to a “dumb” charger.
Note: logic threshold chart: http://www.interfacebus.com/voltage_LV_threshold.html
ATmega has a logic high threshold (VIH) of VCC * 0.6 (min).
For VCC=3.3V, VIH= 1.98V. So you can read the D+/D- as digital I/O levels for V-USB.
The FT230X isn’t particularly new; Hackaday featured an article about my breakout board for the chip a while back: http://hackaday.com/2012/05/11/usb-connectivity-that-is-so-very-very-small/
or mine, for that matter.. :)
http://hackaday.com/2013/04/06/rolling-your-own-minimal-usb-to-serial-arduino-programmer/