The ideia is to start a Bicycle odometer project, an instrument used to measure cruising speed of a bicycle. It accomplishes it by using a single reed (magnetic) sensor.

I plan to use an ESP8266 ESP-12 as the brains and six (6) LEDs to show the speed in increments of 5km/h. The product will be supplied by a 3,7V 400mAh Lithium battery, having a TP4056 board as the battery charger.

As already stated, the speed sensor will be a single reed switch paired with a magnet on the wheel. I plan to implement a RC low pass filter for the sensor to be read by the ESP-12.

The six LEDs will be charlieplexed, consuming only three pins of the ESP-12. The idea is to have each LED represent an increment of 5km/h in speed: 5+, 10+, 15+, 20+, 25+, 30+ km/h.

The idea is to make the ESP-12 sleep when there is no bicycle movement for more than 20 seconds, and have pin GPIO 16 wake the systems up when there is movement. Pin GPIO 16 will be the reed sensor pin, doubling its function: wake the system up and measure speed.

All the project code and schematic/PCB will be in this Github. Here is a sneak peak in the schematic diagram: