Download firmware (bootloader): https://github.com/micronucleus/micronucleus (in firmware/releases/t85_default.hex) Program with ArduinoISP: "C:\Program Files (x86)\Arduino\hardware\tools\avr/bin/avrdude" -CC:"\Program Files (x86)\Arduino\hardware\tools\avr/etc/avrdude.conf" -v -pattiny85 -cstk500v1 -PCOM4 -b19200 -Uflash:w:t85_default.hex:i -U lfuse:w:0xe1:m -U hfuse:w:0x5d:m -U efuse:w:0xfe:m
Upload arduino sketch: Install micronucleus drivers (in micronucleus driver installation folder) Install digistum in Arduino IDE: add to board url http://digistump.com/package_digistump_index.json Install "Digistump AVR boards" under the Tools... Board... Board Manager... Choose Digispark default 16.5MHz.
You must insert / reinsert the ATTiny85's USB plug after the sketch has compiled and is ready to upload.