L7805CV won't go higher than 7.5
The link recommends a fairly moronic way to increase the voltage from a 7805, and incorrectly equates the 78xx parts with the LM317. 

One of the differences is that the internal currents (a few mA) that the regulator uses goes out the output of an LM317 and out the GND of a 7805. The ADJ terminal of an LM317 typically sources 50uA of current, not 5-8mA, so a resistor divider is reasonable. The LM317, OTOH, has a requirement for a minimum output current to keep the output in regulation. The 7805, since it dumps the internal current out the GND pin works fine down to no load. 

If, for some reason, you want to increase the output voltage of a 7805, use a zener diode between the GND terminal and ground, 6.2V will give you 11.2V out. 

The dropout voltage of a 7805 is around 2V typical at 1A (somewhat less at lower current, can be worse over temperature), so if you want 12V out, you need to give it 14 or 15VDC in.