Project #3 in Dhananjay Gadre’s book is an RGB color mixer. It again uses an ATtiny13, this time to drive a 3-watt RGB LED to whatever color the user dials in.
Because the current is higher, the components are larger through-hole versions. There is a TO-220 transistor plus heat sink for each channel and a small block of aluminum under the LED to dissipate heat.
To utilize six pins on an ATtiny13, the reset pin must be disabled, which means it must be programmed in a high-voltage serial mode.
I wrote build instructions as my third Instructable.