This article is part of our “Get Coding” series.
The clever people at Ozobot taught the Evo some nice little tricks. The robot has sensors on the bottom that can determine the color of the material underneath. Given a row of those sensors, the Evo can follow a line. Here’s a little diagram to help.
In this diagram (looking from the top down), you can see the seven color sensors on the bottom of the Evo. Sensors 1 and 2 (on the left side of the Evo) read “white”. Sensors 3, 4, and 5 read “black”. Sensors 6 and 7 read “white”. From this, the Evo knows it is on top of a black line. If it strays to the left or right too far, the sensors will detect this and be able to compensate by telling the wheels to turn a bit.
The Evo is even smart enough to follow curved lines by using this same pattern – read the color underneath all seven sensors, and update the speed of the wheels to keep following the line.
Now, there are a few important details. First off, the line has to be about 1/4″ thick so it gets noticed by multiple sensors. Otherwise the Evo gets confused. Second, the Evo can only figure out changes in the line (turns, curves, etc) a little bit at a time. If the line zig zags all over the place, the Evo will get confused.
But wait, there’s more! The Evo has another trick up its sleeve. Since it can read colors, and since it has a little bit of memory, the robot can detect a sequence of colors and interpret those as instructions. Welcome to programming by markers or stickers! Here’s another diagram to help out.
When the Evo detects a color, it takes note of the how long the color lasts and what color (if any) comes after it. So if the black line becomes red and stays that way, the Evo just starts following the red line. But if the colors switch around as in the diagram, it compares the sequence of colors with the chart below. If it finds a match, it will do the behavior from the chart. In the diagram, the Evo reads “Blue + Red + Green”. If you look at the code chart below, you’ll see that “Blue + Red + Green” tells the Evo to “Go Right”. That way the robot knows which way to turn when it reaches the intersection.
Getting Started with the Experience Pack
The easiest way to get used to these color codes is to use the Experience Pack from Ozobot (link to website or download PDF). As of the time of writing this article, Ozobot will actually send you one for free if you fill out their form, but you can also print it yourself from the PDF and use the markers that came with the Ozobot (or any other blue, green, red, and black markers).
The Experience Pack will let you practice, going from “complete the path” all the way up to a simple maze.
Once you’ve worked your way through the Experience Pack, you’re ready to keep going with Color Codes or proceed to Visual Programming with Ozobot Blockly (next part of our series coming soon)!
As a side note, the Ozobot Evo App for your tablet or phone has a section under the “Play” menu for the Experience Pack. This isn’t necessary, but it will award badges for completing various tasks along the way. If your kid likes to get rewarded for their progress, let the App do its thing.