Manipulating the internal clock of an Attiny85 with a heat gun
The internal clock of the Attiny is quite sensitive to the temperature of the chip.
We made a setup with two Attiny85 microcontrollers with the same code generating a 100 Hz square wave.
The output pins of of the two Attiny85s was connected to the terminals of a speaker.
By heating one or the other Attiny the frequency changes. It is very audible, how the two square waves goes in and out of phase.
We heated the chip with a reflow soldering iron with a precise temperature control. (To avoid accidentally frying the Attiny.