This small FM transmitter circuit uses a 9 volt battery for its power source.
With 16 parts, this is actually one of the larger number of parts for FM transmitters listed on my site. However, that’s still a relatively few number of components, so it is not that difficult to build. (source – http://www.uoguelph.ca/~antoon/circ/fmt4.html ). You can also buy an FM transmitter if you would like. If you don’t want to buy one, then I suggest going through the list of parts and sourcing them from a place like DigiKey or Mouser electronics.