Building a resistor substitution decade box

[George] built an incredibly tidy resistor substitution decade box. These devices feature a pair of connections and a way to select the resistance between the two of them. In [George's] case it’s a pair of banana jacks and these eight thumbwheel switches.

What you see above is the side of each thumbwheel switch. These are panel mount devices which show one digit with an up and down button to change the setting. As you can see, the PCB for each provides connections to which a set of resistors can be mounted. This is the difficult part which he goes to great lengths to explain.

At this point he’s got the resistor groups for each digit soldered in place, the next step is to stack the switches next to each other and connect them electrically. From there it’s off to a project box in which they will be mounted.

This project does a great job of explaining the assembly process. If you’re interested in the theory behind a substitution box check out this other project.

Children’s light up toy is an easy hand-made gift


While this year’s Christmas lists are dominated by electronic gadgets and other mass-produced toys, it wasn’t always like that. We’re not trying to sound like the old man yelling at the neighborhood kids to get off his lawn, but many of today’s gifts lack the personal touch found in old, hand-made toys.

[henlij’s] son is a budding electronics geek who loves playing with switches and lights, so he was inspired to build him a fun toy to pass the time. He constructed a simple box full of lights and switches that his son could toggle on and off to his heart’s content.

While there’s not a ton going on inside the box, we think that the idea is fantastic. With just a few dollars worth of simple components, anyone who knows their way around a soldering station can build something that will keep a child fascinated for hours.

There’s no reason to stop at buttons and lights either. If we were to build one, we would swap the bulbs out for LEDs, then add a wide variety of switches and dials along with speakers and any other components we could get our hands on.

The options are pretty limitless, so if you happen to know a child that gets a kick out of playing with buttons and switches, why not make him or her something special this year, much like [henlij] did for his son?

[Dino] tells us about transistor-based on/off switches


You know them, you love them, you take them for granted – they are single push button on/off switches. As [Dino] explains in the most recent episode of his Hack a Week series, they are typically implemented in the form of IC logic switches nowadays, but it wasn’t always that way. When they first came on to the scene in the 70’s, the single button soft switches were built using a set of transistors and a capacitor to get the job done, so [Dino] decided to research push on/push off transistor switches a bit and build his own.

After reading through a short tutorial, he was ready to go. As he explains in the video, the operation of the switch is fairly simple, though he did run into some odd issues when he prototyped the switch on a piece of breadboard. He’s looking for someone to explain why the unstable circuit suddenly performs better with the addition of a small capacitor between the battery’s positive lead and the circuit’s output, so if you have some insight, be sure to speak up in the comments.

In the meantime, check out [Dino’s] exploration of push on/push off switches below.

[Read more...]

Twittering wall switch lets Dutch hackers know when it’s time to play


Hack42, a hackerspace in Arnhem, Netherlands recently moved into some new digs, and they wanted an easy way to let their members know whether they were open or not. Fixed hours of operation typically do not fit this sort of organization, so that was out of the question. Instead, they built a switch into the wall** that will let their members know when they are open for business.

The switch separates the TX and RX pins of two Ethernet ports that reside in an old access point embedded in the wall. When the hackerspace is open, the switch is thrown and the circuit is closed. A cron job checks the state of the eth1 port once a minute, sending the “Open” status message to Twitter and IRC once it notices the status change. When the switch is thrown again and the eth1 port goes down, a “Closed” message is broadcast.

It is a simple but cool hack, and quite befitting of a hackerspace.

**No direct Google Translate link is available, though Chrome will translate it for you without issue.

[Thanks, _Danny_]