Sukander decides the first one to make will be a cadence sensor. Made from two reflective infrared(IR) sensors mounted on top of the chain ring pointing at the teeth of the sprocket, they will be able to measure the presence and absence of the teeth of the cog as it is turned by the cyclist so producing a pulse determined by the speed of cycling forwards or backwards. It sounds simple in theory and brilliantly Sukander realises it fast and its mounted on lab bike. Turning the pedal steps through a sample producing a kind of time stretch and pedalling backwards plays backwards through the sound. Great. Another product of bike instrument is that it encourages all kinds of weird cycling, standing on top of the pedal rocking and backwards and forwards grinning being one. Note that our cadence sensor also needs a microcontoller with which to connect it to the Pi, simply as the Pi is/will be already busy running its OS handling the GPS, audio playback etc, and a dedicated mc, such as the Teensy, see below, will make a faster system, avoiding any latency.