FigZ:
way ahead of you there ...
when I use the computers usb ports all is fine!
just this usb 1.1 hub
I have not looked into it that much further - it doesnt bother me since I figured out a way to measure the vcc
which actually was a good idea since I need this when I want to run my arduino off batteries.I just got fascinated by the whole bandgap idea because it doesnt involve sacrificing an analog pin.
thanks for your reply, and thanks for sharing your bandgap experiments
Your welcome, and bandgaping was fun but CB did most of the heavy lifting. I just wanted to see if it could be useful or not and wouldn't stop bugging him for help and ideas. To tell the truth I almost never find my projects using all the analog input pins (and if so I just switch to the mega board or my 644P soon to be 1284P board, so just tying the 3.3v to a AI pin and using that as a compensation/refence value is simple enough. Heck on one of my boards I have a jumper from the anode of the power led wired to a AI pin as a reference, it works.
But for serious ADC results I just use I2C ADC chips, either the TI 12 bit ADS1015 for 16 bit ADS1115, they are what real ADC is be all about. Adafruit has some nice breakout boards for them and has support library all set to go.
Lefty