My little girl loves pressing buttons. As soon as she became aware that buttons existed she was drawn to anything that has them. If the buttons actually do something, she’s absolutely enthralled. She’s a good kid, even as a toddler under the age of two, so she doesn’t tend to mess things up too often by, say, pressing the power button on the family XBMC machine or mashing remote controls left on the coffee table (though she does carefully press the buttons she’s familiar with).

I gave her a cheap keyboard a while back, which she enjoys playing with, but since it isn’t connected to anything, the fun of pressing those buttons wears off pretty quickly. Months ago I envisioned building a simple toy that would consist of little more than buttons and lights, with each button press activating a light of some sort.

Concept

Enter the LED Button Box! Six colored buttons, each controlling a colored LED, with a power switch and a small LED to indicate the power is on. Despite having a fair amount of experience with basic electronics and being capable of wielding a soldering iron with slightly greater than beginner skill level, I had to do a bit of reading to understand what I was getting myself into. Here’s the stuff I studied before I went out and started shopping for parts:

• Nearly everything you need to know about Light Emitting Diodes
• Resistors for LEDs

Once I had a grasp of what I wanted to build and how to piece the components together, I put together a shopping list.

Components

• (6) 10mm Diffused LEDs (red, blue, white, yellow, green, orange)
  • Amazon, or
  • Sparkfun
• (1) Toggle switch
• (6) Colored Tactile Buttons
• (1) 5mm violet LED (they’re so inexpensive, go for a variety pack!)
• 25′ red stranded wire (unsure of the gauge, I had this lying around already. Smaller is better)
• 25′ black stranded wire
• Solder
• Industrial adhesive (I used this and it worked very well)
• (1) 3x AA battery holder, with wires
• (10) 39 Ω resistors (I bought resistors at Jameco but you can also try Amazon)
• (10) 51 Ω resistors
• (10) 100 Ω resistors (didn’t end up using these)
• (10) 330 Ω resistors
• Medium sized acrylic box Updated: IP66 Polycarbonate Box (safer, stronger than original acrylic box featured in this post; I rebuilt this toy after the original box failed)

I also used the following tools, which you’ll need for this project:

Tools

• Soldering Station (I can’t possibly recommend anything less than the X-Tronic 4000 series. Don’t even bother with the cheap $12 Radio Shack soldering iron. Seriously.)
• Wire cutters
• 90 Degree needle nose pliers
• Wire stripper (I actually used a pair of scissors because I couldn’t find my strippers)
• Cordless drill (I prefer the Makita 18V but anything that can drill holes will work just fine)
• Drill bits
  • 1/16″
  • 3/32″
  • 1/2″
• Sharpie for marking where to drill your holes

Guide

Preparation

Just making sure I actually know wtf I’m doing before I go soldering things up!

Before I even started marking where I would drill holes, I wanted to make sure I understood how to wire up the components I had purchased. So I loaded some batteries into the battery case I bought and experimented with an LED and some resistors. I quickly realized I had no idea how to even determine which resistors were which, so I made liberal use of this handy resistor color code calculator (I actually bought a wide variety of resistors, much more than what’s in the parts list above. And they arrived un-labeled).

Once I understood how to use those parts, I tried adding a button into the mix. The buttons I purchased have four contacts, which turned out to be super useful once I did a little testing with a multimeter to figure out what those extra contacts are for. Here’s what I learned:

How to wire a 4-contact tactile switch for the LED Button Box

It doesn’t matter how the switch is oriented. The diagram to the left applies regardless of which contact you decide to use as your input. It was definitely handy to have that bypass output contact, because it meant I didn’t need to do a ton of splicing inside the box. Instead, each switch’s input was connected to the previous switch’s bypass output. Pretty cool!

Build It!

First, lay out the parts on top of the box, then break out a ruler and sharpie and mark where each component will be installed.

Place your components in roughly the position you’ll be installing them to get an idea of where everything will go before you begin marking and drilling

Next, drill two 1/16″ holes for each LED. I didn’t measure the distance between the LED leads, I just eyeballed it and it worked out pretty well. Go ahead and glue the LEDs into position with the high strength adhesive you got for this project.

You’ll use adhesive to secure the LEDs to the box after drilling your holes

Buttons are next. I thought I would be able to mount the button bodies inside the box and have just the caps sticking out, but the box I got was too thick so I wound up drilling holes for each contact instead, and mounting the buttons to the top of the box. I used a 3/32″ bit to drill the holes so it would fit the leads and soldered wire. This is also where I broke the top of my acrylic box by pressing too hard when I drilled the first hole. After that was repaired, I let the heat of the drill bit do most of the work and used minimal pressure to avoid additional cracks in the plastic.

Four 3/32″ holes for each tactile button

As you can see in the photo above, I also glued the battery holder into place. Pretty simple.

Next, I mounted the power switch on the side of the box. The body fit inside the box, with the actual switch protruding from a 1/2″ hole I drilled. This particular switch worked perfectly for the project, its hex nuts making it simple to secure the switch to the box without the need for adhesive.

Switch installed on side of box. 1/2″ hole was drilled and the component fit perfectly

Now it’s time to heat up the soldering station. My first soldering task was connecting the resistors to the positive lead of each LED. As you can see I’m not too great with a soldering iron, but hey it gets the job done 🙂

Resistors soldered to LED positive leads

Then I installed one button, in order to confirm that the overall design would function as I expected. After wiring this first button, I turned the power switch on. connected the negative lead from the battery pack to the negative contact on the first LED, then pressed the button. To my delight, it worked! So then I cut wires and put them into position in preparation for a bunch of soldering.

First button installed and wires cut, stripped, and placed for soldering to remaining five buttons

Another view of button wires in place and ready to be soldered to other buttons

Once all your buttons are wired up, with positive wires soldered in place, all that remains to install is the negative (black) wires connecting all the negative leads from the LEDs to each other, and then to the black wire coming from the battery pack. Since I am truly untalented with the soldering iron, my solution for this is rather unsightly. See below…

Black wires connecting negative terminals of each LED

Once the whole unit was functional, I decided it would be a good idea to have an LED indicator when the power is switched on. So I drilled a couple holes above the power switch and added a 5mm violet LED, then wired it up using available leads from the power switch and an LED. This LED was a little too bright, so I used a 330 Ω resistor on it so it remains suitably visible without being overly distracting.

Power LED lights up when the unit is turned on.

And here are a couple more shots of the completed device, fully functional.

Top-down shot of the finished product, completely wired and fully functional

Inside of LED Button Box while a couple buttons are activated

Final notes

Small Parts

When I first showed this to my daughter, within 90 seconds she had removed the caps from two of the buttons, which I immediately realized are fantastic choking hazards for a small child. So, I glued those puppies tightly to the button bodies. Another issue is that she also quickly figured out how to open up the box and started touching the insides. This isn’t especially dangerous, but it is likely to result in a non-working toy pretty quickly. So I used a small piece of nylon strap and screwed it into the top and front side of the box. I’m pretty sure that the screw holes will strip out after a half dozen battery changes, so hopefully I can come up with a better solution by the time that happens. Although, considering the batteries will likely last a very long time in this device, I may not even wind up changing them that often… my girls might outgrow the toy before we go through 15 AA batteries!

LED Brightness

I won’t attempt to even begin to theorize about the inner workings of a 21-month-old’s brain, so what I’m about to describe is highly mysterious to me but warranted a revision to my design nonetheless. This may not apply to older children, or really any children other than mine.

After about five minutes of playing with her brand new LED Button Box, my little girl began placing her eyeball directly over the brightest of the six LEDs (white) and pressing the button to activate it. She thought this was hilarious, but of course I’m sitting there wondering how many times she can do that before she permanently damages her eyesight. So I decided to reduce the brightness of the brightest two LEDs (white and green) by pulling the existing resistors and installing higher ohm resistors in their place. After some testing, I settled on a 470 Ω for the white LED and 390 Ω for the green. Now they are still bright enough to enjoy but not so bright that I worry it’ll blind my kid if she stares at it for a few seconds. And of course I’ll also be discouraging that behavior.

Future Revisions

This toy could be more fun with a variety of upgrades. Some ideas I’ve already had:

• Have each button generate a tone, like different beeps (might get very annoying to nearby adults, but I suspect children will really enjoy it)
• Add a couple “special” buttons to trigger pre-programmed functions:
  • Light show (flicker random lights while button is pressed?)
  • Activate all LEDs
• Add a new mode, with a selector switch to enable it, that would make the lights flicker or strobe with each button press, rather than just remain steadily lit

There are so many things one could do to make this toy more interesting, but most of them will require the use of a microcontroller, and that is a bit beyond my capabilities right now. Perhaps next winter I’ll be ready to tackle something more complicated as a holiday gift for my kids.

If you have built electronic toys for your kids I would love to hear about it. Please link similar projects in the comments section below!