Re: volts.py output problem
First observation is the code on at least some of the SD cards is definitely different, even though I purchased them all together. When I went through my own setup steps, a few things were different. The raspi-config system is totally different options.
Looking at a scope, I see there is a problem during the read sequence, which is driven from the Pi side. I can't tell if it's in the chip hardware or somewhere in the software driver for the i2c on the Pi side.
Here are a couple notes I am hoping some of you can play with. Then I will post a bunch of screen dumps in a follow up post of the suggestions you guys had above....
This may be a relevant post:
The person says they solved their problem "I had to load the module i2c-bcm2708 additionally to the already loaded module i2c-bcm2835. And after doing this I got a new folder in the /sys/module/ directory named i2c_bcm2708."
I don't know how you would load a module into an already loaded module. (Don't you just HATE HATE HATE when someone says they fixed it but don't post an actual command?).
Anyway, I think this problem is somewhere in one of the smbus modules or the low level i2c driver.
On both units I run lsmod.
On the working unit, I have i2c_bcm2708
On the non working newer unit I have i2c_bcm2835
I'm really hoping someone can help on this. I'll put some dumps in the next post. Thanks everyone. This i2c thing is critical to making the whole thing work like it's supposed to. I can say I'll never design anything with a Pi ever again. Dealing with that thing took a simple project and added about a thousand hours of un-necessary headache.