Pilaobo is an interactive robot built with a ATtiny85 microcontroller, two servos and one ultrasonic distance sensor and it can be used as base for any other simple robot.
When something gets close to it, it moves both arms between 45 to 135 degrees. The robot stops when it cannot detect anything close to it anymore.
It depends on the DigisparkSoftRcPulseOut library available on Arduino Library Manager.