Quantity   Component name
1 × Teensy 3.1 starting point, can eventually consider alternative uC
1 × 0.96 I2C OLED screen OLED is simpler (monochrome) and nicely readable in daylight
1 × LiPo battery charger with protection circuit (TP4056+DW01)
1 × LiPo battery (1s, 100-500mAh) small enough to fit inside a case, large enough to last a couple of days
1 × Bluetooth serial module HC05 Optional: to communicate with Android device
1 × Latched bipolar hall effect sensor 3.3V (FS177) To measure wheel revolutions using two opposing magnets
2 × Strong magnets