All posts in Electronics

Moon Phase Purse

I’ve been going through a moon phase recently (pun absolutely intended), and thought it would be fun to make a wearable or totable that displayed the current state of the moon. There would be a bit of hardware involved, so a purse seemed like the perfect vehicle—you’re already carrying a load of other things, so there’s no harm in the addition of a small battery pack or a pile of LEDs.

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Molotov Cocktail LED Lantern

LED candles not radical enough for you? How about some revolutionary chic in the form of an LED molotov cocktail! Let’s call this number two in my series of bad ideas sure to draw the attention of the local constabulary, the first being the screwdriver key that lets you “steal” your own car. Read on and learn how to make your own.

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Every year I throw an Oscar party with my friends, with lots of drinking, yelling at the TV, and low-stakes wagering. Everybody puts in a dollar as each category is announced, then that pot is split among everyone that made the right pick. After almost 20 years of doing it the same way, I finally got tired of counting out the change after each win. $1.65 times nine winners equals clinking coins for minutes.

So why not do what grocery stores and fast food restaurants figured out long ago and automate the change dispensing so any middle-school dropout can do it? I present to you the Change-O-Matic.

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The Counting Box, Version Two

My Counting Box article in MAKE magazine was meant as a short “How I Made This” story, not a detailed “How You Can Make This Yourself” guide. Because people might want some instructions to follow in order to make their own counting box, I built a new version and documented it.

But first, an update on Counting Box Version 1. It’s been in service for 17 months and is showing a count of 121,860. This is three less than the highest number it’s reached. My son doesn’t seem to be a fan of negative numbers because -93 is the lowest the box has counted. The increment button has been pushed 18,422 times and the decrement button 4227. It’s only been recharged twice that I know of, so that giant battery was total overkill.

Now here’s how to build your own.

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What do you get when you combine a pumpkin with the classic video game Tetris? Pumpktris! Fully playable, embedded in a pumpkin, and with the stem serving as a controller. Watch the video below to see it in action, then read on for the development story.

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iPhone-Charging USGI Flashlight

Last week I ordered a MintyBoost charging kit from AdaFruit. The MintyBoost is a circuit that takes power from a pair of AA batteries and outputs 5v through a USB port, so you can charge your phone or other similar device where you might not have access to another power source. It gets its name because it’s commonly built into an Altoids mint tin, but I wanted something a little heavier duty than candy and tiny batteries.

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The Counting Box

My son—now four, but three when I conceived this project—loves numbers and counting. More than a few times I’ve peeked in at night to find him asleep with a calculator in one hand and a flashlight in the other. And one of his favorite things to do with the calculator is incrementing “1 + = = = = = = = = = =” until he can’t keep his eyes open any more. I decided to build him a dedicated machine that would do nothing but count up and count down.

My initial concept was simple: a seven segment LED display so it could be read in the dark,  a rotary switch in the middle to choose the value to operate with, and big buttons for adding and subtracting.  Green makes the number get larger and red makes the number get smaller.

Below is the finished product. Click the “Continue Reading” link under the picture for details about the process of building and programming. I didn’t take a lot of photos through the build process because there wasn’t much to see, so I’ll illustrate relevant parts of the writeup with photos of the finished counting box. Also, please be aware that this is meant more as a documentation of my build process and the things I learned, rather than as a step-by-step how-to guide to make your own. I hope you’re still able to learn something or be inspired.

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Snap Circuits Repair

For my birthday a few months ago I got the SC-300 kit from Snap Circuits, and it’s been a great way to share electronics with my son as well as having fun myself. Overall, I really like the set, but my biggest complaint is that I’d like to see more explanations of the circuits, rather than just the assembly guide it has now. Why use a 100Ω resistor instead of 100kΩ? What’s that transistor doing? Curious minds will be left wanting answers to questions like these.

But anyway, on to the repair…

The C1 piece, a .02μF capacitor, broke off at one of the legs. This is understandable, since the capacitor sticks out to be bent and squished accidentally by clumsy fingers.

If you look closely, you can see the broken right leg.

You can order replacement parts, but the shipping cost was prohibitive. Time to crack the case and peek inside! A fingernail and a small flat screwdriver (the size you might use to tighten screws on your glasses) popped the part open at the tabs without too much trouble, but be careful because if you crack the plastic that’s going to be a lot harder to repair than a wire inside.

Looks simple enough.

The local Radio Shack didn’t have any .02μF capacitors, but they did have .022μF. We had circuits to build right away, and it should be close enough for everything in the kit. If I feel like getting it exactly right later I’ll add a .02μF to the parts order for my next project.

Close enough.

The leads desolder easily, but be sure you don’t keep the heat on too long or you might melt the plastic directly underneath. Put the new part in through the holes in the case, bend the leads, then trim them to fit the tabs. The tabs don’t have any holes for the leads to go through, so just hold the lead onto the existing solder and heat it up. When it was done, the bottom half of the case clipped right on and we were back in business.

All fixed up and good as new.

UPDATE 1/21/2013: A commenter reports that you can order free replacement parts at If you need to build that AM radio right away you could still fix things yourself, then order a replacement at the same time.

Backlit Skeeball Marquee

Some of my earliest dates with my wife were playing Skeeball at the Seaside arcade. I wanted to commemorate those good times, but our house doesn’t have room for a full Skeeball game, so I thought I’d give her the next best thing — a backlit scoreboard.

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