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.
Continue reading →
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.
I’m trying to set up a beginner’s electronics workbench, but organizing all of the components has been a hassle. I’ve got a cabinet with sixty-something little plastic drawers, but that seems inefficient for resistors when I might only have 5 of a particular value. It works well for other pieces like switches, buttons, and connectors, though.
I tried using small plastic envelopes in a recipe organizing box, and while it was nice being able to see them when an envelope was out on the desk, the envelopes were too floppy and it was impossible to flip through and find what I was after.
Then I remembered an unused two-drawer card file tucked away at my parents’ house that would be ideal. A2 envelopes were a perfect fit, and there was a sliding backstop in each drawer to keep it all packed tight.
Being a newbie to this electronics thing, I hadn’t yet memorized the resistor color codes, so I decided to print a color guide on each envelope along with the numeric value. The funny thing is that by making all of the envelopes in InDesign I’ve gotten pretty good at the color code system. I think they’ll still serve well as a check when I’m putting resistors back after a prototyping session.
The other night, with the envelopes all printed, I huddled over the piles and started sorting. First lesson learned: good light is a must. Under my lamp, red looked the same as orange looked the same as yellow. Brown and black? No difference between them! Eventually, with a few illuminations from a super-bright flashlight and a few particularly troublesome ones set aside for the morning, I got everything in its place and filed away.
Here’s the finished system. The resistors only take up about half of one drawer. What should I keep in the second drawer?
