Schematics and PCB layout made using KiCad (http://kicad-pcb.org/).

ATTiny85's firmware is built using PlatformIO (http://platformio.org).

Before uploading the firmware I used the Arduino IDE and an "Arduino as ISP" to burn the 8 Mhz bootloader, you may get incorrect timing otherwise. I have not yet bothered to figure out how to do this with just PlatformIO.