Quantity   Component name
1 × ATtiny85 Microprocessors, Microcontrollers, DSPs / ARM, RISC-Based Microcontrollers
1 × Analogue Voltage Meter We've used 15V meters but other ranges will also work (as long as you rescale them properly)
2 × NPN transistor Used to detect signals from the magnetic sensor and to drive the voltage meter
2 × 10kΩ resistor Used to limit the current going to the reed switch and to control the voltage meter (via NPN)
1 × 4.0kΩ resistor Used to change the voltage range of the voltage meter
1 × CR2032 Coin Battery One battery should power the device for few months
1 × Voltage Regulator We've used Pololu step-up voltage regulator with shutdown pin
1 × Sigma magnet & reed switch The reed switch and magnet combo can be bought without the bicycle computer
1 × Blue LED Used for illuminating the dial
1 × 220Ω resistor For the LED sub-circuit