Niftymitter is an open source short range FM transmitter based on the open source hardware design by Tetsuo Kogawa.

Version 0.1 is designed to be housed within a 3mm acrylic or bamboo body, with a variety of options for hacking. The transmitter is tiny and handy for small scale radio broadcasts, building a distributed PA system for performances, linking your personal audio player to your car radio, or for general audio experimentation.

I am currently working on v0.21 which is a bit of a radical redesign, so v0.1 is posted for completeness.

ISSUES in v0.1:

• too bulky
• acrylic prone to failure at corners
• cable tie construction troublesome - not very secure, ends tend to catch on things.

The project's home is at http://www.openthing.org/products/niftymitter

As this is now a deprecated design, I am working on more complete instructions for v0.21. The main thing you need to know if you want to make this version is that the electronics are described on Tetsuo Kogawa's site here:
http://anarchy.translocal.jp/radio/micro/howtosimplestTX.html

And I used this switch from Rapid (UK supplier):
http://www.rapidonline.com/productinfo.aspx?tier1URL=Electronic-Components&tier2URL=Switches&tier3URL=Push-Button-Switches&tier4URL=Miniature-SPST-LED-latching-push-switch&moduleno=71429&kw=78-0188

This thing is so wee, it makes more sense to cut two at a time, so the file contains parts for two.