Computer Logic Lesson #3: Crossovers

A few weeks ago we dug into how ramps are like wires in an electronic computer. This 3rd installment of the educator guide explains the importance and role of the crossover. When most of your class has started puzzle 5, you can pause to share this lesson with them. When I worked with 4th grade classrooms at our local school, I found the attention getter “Eyes up, marbles down!” worked well. Also, if you can pull apart an old appliance or computer and pull out the circuit board, that is even better! The older the circuit board is, the more clearly you can see the wires.

Computer Logic Lesson #3: Crossovers

In puzzle 5, the “crossover” part is introduced. It looks like this:

The purpose of the crossover is to let the paths of the marbles cross over each other. A marble coming in the left side exits on the right. A marble coming in the right side exits on the left.

What do crossovers look like in an electronic computer?

The crossover acts like two wires crossing over each other, but not touching each other. Electricity can move along each of the wires, but the crossing paths don’t interfere with each other. It would be impossible to create complicated circuits without wires that cross.

Because the crossover allows the paths of the marbles to cross over each other without interfering with the path of the next marble, they are performing one small component of what happens in a circuit board.

Circuit boards are used in electronic computers to keep all the wire connections sturdy, safe, and fixed in place. A circuit board is made of a hard, flat material. On the surface is a thin layer of copper, etched into a carefully designed pattern of wires that connect the electronic components on the board. A circuit board is comprised of many more elements than just crossing wires. Circuit boards house transistors, CPUs, and much more. Below is an example of a circuit board. You can see the copper wires connecting all of the electronic parts.


If the wires on a circuit board are all on a flat surface, how do they cross over each other without touching? Most circuit boards actually have multiple layers of copper wires sandwiched between insulators. Little holes called “vias”, connect wires in the various layers of copper.  In the picture above you can see lots of little vias connecting the various layers of the circuit board, allowing the copper wires to cross over and under each other without touching.

In computer chips, there are also multiple layers of tiny wires that cross over and under each other, sort of like how overpasses allow cars to drive over other roads.

(Yan'an East Interchange, Shanghai, China – Getty Images)

 As you work through the challenges with your students, you will unlock more parts. Our educator blog and our educator guide share how each of the parts in Turing Tumble correspond to the parts in an electronic computer. This tangible interaction with a mechanical computer will allow students to see, hear, and feel how a computer works. Enjoy watching the discovery as their minds are opened to engaging STEM with more confident exploration.

Leave a comment