Only two components are required, assuming that you have the iPhone:
- Application "Freqgen" which is free and available in the AppStore.
- Adapter that you have to make. Construction is very simple, and the whole process is shown further in instructable.
Step 1: Freqgen
Frequency is selected by typing the numeric value in the box with the keypad, rotary selector, using a small keyboard at the bottom of the screen, or by shifting octaves with octave up/down buttons.