Snap your circuit together
This project uses USB power -> cloudBit -> Oscillator -> Synth Speaker
Connect your cloudBit
Follow these instructions to connect your cloudBit to Minecraft: http://discuss.littlebits.cc/t/bitcraft-our-minecraft-mod-is-live/22949
Lay down your minecraft track
Put tracks down in a circular shape (so the pattern will repeat itself). Place detector plates where you want your notes. I put booster tracks everywhere else so the minecart wouldn't slow down during it's ride.
Connect redstone wire to your detector plates
Connect redstone wire to each of the detector plates you put down previously. The length of the wire will determine the note that is played: shorter wires will make higher notes, while longer wires will make lower notes, almost like plucking a string. You can make your wire as long as 15 blocks!
Short wires make high notes
Long wires make low notes
Connect the wires to the Cloud Gateway
Place a Cloud Gateway block a the end of each wire, so the orange connector is facing the redstone wire. Make sure they're all set to "Transmit", and connected to the same cloudBit. As the minecart travels around the loop, your cloudBit should receive signals from all of the Cloud Gateway blocks.
Put a cart on your track to play your song
Place a cart on your track and give it a push to hear the result! Try changing the wire lengths for different notes. Also, you can adjust the octave with the oscillator knob.