This sensor only responds to 38 KHz modulated infrared light which makes it immune to disturbance caused by the ambient light. Specifications of a typical Digital Infrared Proximity Sensor module is ...

It should be a piece of cake if you program your Attiny85 chip (not Digispark) using your existing Arduino IDE with the help of one “USB tiny ISP (v2.0)” programmer. The software/Arduino sketch /* * ...