MP3 Cassette Solution

Step 2 The trusty Cassette Adapter

These can be found nearly anywhere. Most major electrical outlets stock them, but they can be bought more cheaply from your local soiled sillys or clazy crarks. Hang onto the cable - this is useful for testing the audio playback before the final solder. The model that I used had a removable audio plug that could be plugged into either of the two 2.5mm sockets.