Circle Tracing

KOI is able to find and track circles in a scene.

Circle Tracing


Load the KOI Extension:

Loading Extensions

Blocks for circle tracing:


Sample Program




Threshold affects the detection rate, testing and fine tuning the value is needed for achieving the best results.

A higher threshold value decreases interference and noise, but detection difficulty increases at the same time, please trial and fine tune for different scenarios.

Program Flow

Download the program to Micro:bit, then press A on the Micro:bit.

The radius of the circle is shown on the Micro:bit while its coordinates are shown on the KOI.

Advanced Program

The information becomes more easily readable if we add an OLED screen.

Connecting an OLED

Connect an OLED panel to the I2C port of your Robotbit/Armourbit.


Sample Program

Load the extension for OLED:


Extension Version and Updates

There may be updates to extensions periodically, please refer to the following link to update/downgrade your extension.

Makecode Extension Update


1: There is no reaction after pressing the buttons on the Micro:bit.

· A: This is because KOI has a longer boot time than Micro:bit. When the power is turned on, Micro:bit has already ran the code for KOI initialization before KOI is ready.

· Solution: Reset your Micro:bit after KOI has been turned on. (The trick is to let KOI power on completely before initialization.)

2: Does KOI work with 3V input?

· A: No, KOI only works with 5V.

3: How do I improve detection rate?

· Adjust the threshold value.

· Keep a clean background.

· Make sure the circle has a sharp outline.