I am using RTC DS1307
and I was curious about the HC-SR04 distance sensor
so I powered Pi off, plugged the sensor and powered Pi on
used http://www.bytecreation.com/blog/2013/1 ... or-hc-sr04
after this the RTC didn't work so I powered Pi off and unplugged HC
then powered Pi on.
the RTC started to work again but time/date weren't set, I had to set it again
unplugging RTC and plugging it back never made me lost it's time/date