Unstable Operation of Arduino (HC-SR04 Ultrasonc sensor)

Hi, have you got filter and bypass capacitors around the voltage regulators, see their data sheet for info.
Can you post a CAD or picture of a hand-drawn circuit diagram in jpg,pdf or png for us please.
Even though you are supplying the voltregs off a battery, the perfomance of the regulators relys on noise and load transient filtering.

Hope this helps.

Tom.... :slight_smile: