Oxygen Sensor

Hey Everyone,
I am trying to replicate the schematic shown here: Blogs de Medialab-Prado | Otro sitio realizado con WordPress where they use a KE-25 Oxygen Sensor with a TLC272 Op amp. However, I cannot find what V2 or U2 is. My guess is some voltage regulator? Also, does anyone have a good link to understand the op amp with the arduino (with code)? Thanks for any insight.

I cannot find what V2 or U2 is.

Where is V2?

U1 is the TLC271 www.ti.com/product/tlc271
U2 is any 5V regulator like an LM2930

Sorry, I meant V2/U2 (I couldn't tell the difference).