It's not circuitry, it's actually just a simple optical reader in the 2.0 machine that looks for the Keurig trademark printing around the rim of the K-Cup. Detractors call it Digital Rights Management (DRM) for coffee, and it's quite unpopular. YouTube is filled with "Keurig hack" videos with various schemes for both defeating their 2.0 DRM as well as hacks for getting access to the full menu for the machine (e.g., for brewing larger cups & karafes).
Regardless, their new DRM system on the 2.0 is easy to defeat. Easiest is to cut off the top from a used K-Cup and tape it onto any old K-Cups you still have around (or 3rd party K-Cups that don't want to pony up license fees to Keurig) to defeat the optical reader.
You can also order a free "Freedom Clip" from http://www.rogersfamilyco.com/index.php/revolution-begun-starts-now-fight-keurig/ that simply snaps into your 2.0 brewer to defeat the DRM system.
I ordered one a few weeks back (it was free) and it just came in the mail the other day. I snapped it in, and now I can use any K-Cup I want. It also makes dispensing hot water for tea or hot chocolate a lot easier because you don't have to hold the button down for that anymore.
The Freedom Clip is just a permanent clip with a colored paper disk that sits right in front of the optical reader. Regardless of whether the machine is empty or what's in it, it makes the machine think there's a valid trademarked K-Cup in the machine all the time. Works great, and easier than taping officially sanctioned foil lids on old K-Cups to defeat it.
BTW, love K-Cups - especially since myself & my wife drink flavored coffees almost exclusively, and never enough to make a whole pot (of boring unflavored coffee :P) worth it.
Thanks for this very informative update.
We have two Keurig machines. Actually one is an 4 year old single cup model (Mr. Coffee) we use in the RV.
I now know that when I go to get another one, I’ll get one that is not the 2.0 version. Even if I have to buy used.