ESP8266 Cycle Computer

Background

We purchased a cycle computer from Sunding and after configuration found that it reported the cycle speed well.

We wished to extract this speed information to show on an WS2812B Neopixel LED strip, but this device did not have any interface to plug an Arduino into it.

How it Works

The cycle computer works in the following manner:

• A magnet is placed on one of the spokes of the rear wheel of the cycle.

• A reed switch is placed on the frame of the bicycle, such that whenever wheel travel around, it will come as close to the reed switch as possible. So every time the magnet passes (on account of the rotation of the rear wheel due to pedaling) the reed switch will sense this magnet, and will make connection. The reed switch was part of the cycle computer package that we purchased.

• The cycle computer has two metal terminal to which this reed switch connects.

• When the reed switch is not physically connected to the computer, the two terminals of the cycle computer read a voltage of 3.3V, which is expected, because the cycle computer runs on a CR2032 3.3v battery.

• So the purpose of the reed switch is to connect the two terminals together, and that is how the cycle computer figures out that one revolution has completed.

• If you can measure the time duration between two reed switch closure events, then you can find out the speed of the cycle, by knowing the circumference of the wheel, because, that is the distance the wheel traveled in the time it took it to make one rotation.