Electronics Project: Sophie’s 3-LED Traffic Light

by Ben N on November 16, 2017


Yesterday, my Crazy Circuits arrived in the mail. After dinner, the Little Girl (Sophie, just turned 7 years old) and I decided we would play with them.

I thought the first thing we would do is a simple LED circuit – just a battery going to an LED. Well, we barely had that done before she wanted to skip straight to something fun and useful, and much more complicated!

IMG_7302She decided that she wanted to make a traffic light! I had already been fiddling with one of the slide switches. Of course, it turns out I was trying to use it wrong. When I actually bothered to read the SUPER EASY INSTRUCTION CARD for the component, I realized it was a two-way switch, instead of just a plain make-or-break switch. Even better than that, the example on the reverse side of the switch card was A TRAFFIC LIGHT project!

But that traffic light only had two lights! I asked Sophie if that was OK. She said ‘No, real traffic lights have three colors, so we have to do that.’

It only took us a minute to realize that our kit had two slide switches in it, and by using both, the combination of switches would allow us to activate any of the three lights. Sophie choose one each of red, yellow, and green of the Lego block LEDs. We fed power from the positive side of the battery to the first switch. If the switch was up, it would route power to the red light. If it was down, it would route power to the second switch. That one was connected so that the up position would send power to the yellow light and down would route power to the green light.

We laid out all the components on the green Lego “circuit board” so we would know where to lay the traces we would make with the conductive tape. If something didn’t look right we just moved the component to where it would complete the circuit and make it easy to run the conductive tape. Once we were happy with our layout, we then put down the tape.

IMG_7558When I was originally explaining how we would design the circuit, Sophie didn’t quite understand. She asked if I could draw it out. So, I did, but I drew it as the electrical schematic. She understood that right away! Who knew that first-graders were so good with engineering diagrams!? I guess that’s one thing that I’ve learned as a parent so far is not to underestimate children.

Looking at what we designed, I also realized that it was starting to look like a really basic computer. At the core of computing is simply a bunch of switches – ones and zeros – depending on the combination of which are on, data can be stored, or something can be created like an image on an LCD television monitor. We had gone from just learning how to light up a single LED to COMPUTER SCIENCE in a span of less than ten minutes!

The conductive tape can be a little small to work with my big fingers, but I found that the laser-cut acrylic components which were included to connect to servos is the perfect thickness to use as a tool to press the conductive tape down between the bumps of the Lego board. The components fit well on the board, the trick is to not use TOO MUCH conductive tape. Just have the tape go over the top of the Lego bump to whatever hole is being used to make the connection to the Crazy Circuits component.

Once the Traffic Light was wired up, Sophie popped in the battery, and the light came on. (The one over her head AND the one on the circuit board!) It’s pretty cool when you can actually SEE those moments of learning!

IMG_7562Using a COMBINATION of the two switches will activate either the Red, the Yellow, or the Green light. All three use a common ground – the negative side of the LEDs all join together and are routed to the negative of the battery. (This is exactly how 12V power works in a car! It’s super common that if something electrical doesn’t work in a car, it’s often a bad connection to the negative ground!)

POLARITY is an important concept, and applies to both batteries and LEDs. The convention with Crazy Circuits is that the positive side is has a color, and the negative side is white. A bit like “Home and Away” sports team jerseys or Regular and Diet soft drink cans!
The colored markings helped Sophie make sure all the polarities were right for the circuit to function.

Sophie then realized that we had no OFF switch for our circuit. I asked her if real traffic lights had an OFF switch. She thought for a moment, and then said “No, they don’t, they’re always on.” When I asked her what would happen if the lights were out, her eyes got big and she exclaimed “All the cars would crash!”

(In a completely unrelated event, I once was driving at about dawn on a very early summer day. I had already driven through several round-a-bouts. It was only when I got to a traffic light that I realized that power for the entire town was still out from a thunderstorm the previous night! Round-a-bouts are designed to work even in a power failure.)

My daughter played with the switches, memorizing which positions activated which lights. Once she had that down pat, she decided we need to do something with it. She quickly improvised a game where she pretended to drive a car, but had to drive based on what I made the traffic light do. Pretty soon we were taking turns driving and operating the lights. We even had conversations on rules of the road, “Right-Hand Red”, round-a-bouts vs. traffic lights, and brought speed limits into the game.

In a bit of trickery, when it was my turn to operate the traffic light, I secretly swapped out the green LED for a blue LED. When she ran the red light, I quickly flipped the switch back and forth, alternative RED & BLUE, I make a police siren sound, pulled her over, and put her in jail! (She had to spend 30 seconds on the sofa.)

All together we spent well over an hour designing a project and playing with it. I can’t think of the last toy that she’s had that could hold her attention for that long.

At the end of all of that, I asked Sophie if she wanted to make a video, showing how her project worked. She said yes. I tried to keep it simple and let HER make the video. She told me just to do an introduction, and that then she would take over. I hit record on my smart phone, did the intro, and she took it from there. That’s the video at the top of this blog entry.

With the one electronic kit, we went from lighting up a single LED to learning about switches, computer science, Drivers’ Ed, civil engineering, car repair, law enforcement, freeform play, and even media production!

I’ll mark this one up as a parenting WIN!

Stay Crazy everybody!



Leave a Comment

You can use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>

Previous post:

Next post: