Diodes: The Switch You Never Knew You Had

Vishay's take on the 1N4148 data sheet (PDF), describing it as a switching diode.
Vishay’s take on the 1N4148 data sheet (PDF), describing it as a switching diode.

When looking across the discrete components in your electronic armory, it is easy to overlook the humble diode. After all, one can be forgiven for the conclusion that the everyday version of this component doesn’t do much. They have none of the special skills you’d find in tunnel, Gunn, varicap, Zener, and avalanche diodes, or even LEDs, instead they are simply a one-way valve for electrical current. Connect them one way round and current flows, the other and it doesn’t. They rectify AC to DC, power supplies are full of them. Perhaps you’ve also used them to generate a stable voltage drop because they have a pretty constant voltage across them when current is flowing, but that’s it. Diodes: the shortest Hackaday article ever.

Not so fast with dismissing the diode though. There is another trick they have hiding up their sleeves, they can also act as a switch. It shouldn’t come as too much of a shock, after all a quick look at many datasheets for general purpose diodes should reveal their description as switching diodes.

So how does a diode switch work? The key lies in that one-way valve we mentioned earlier. When the diode is forward biased and conducting electricity it will pass through any variations in the voltage being put into them, but when it is reverse biased and not conducting any electricity it will not. Thus a signal can be switched on by passing it through a diode in forward bias, and then turned off by putting the diode into reverse bias.

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DIY KVM Switch Lets You Use One Keyboard and Mouse With Multiple Computers

Here’s a quick DIY hack if you happen to have multiple computers at home or at the office and are tired of juggling mice and keyboards. [Kedar Nimbalkar] — striving for a solution — put together a keyboard, video and mouse switcher that allows one set to control two computers.

A DPDT switch is connected to a female USB port, and two male USB cables — with the ground and 5V wires twisted together and connected to the switch — each running to a PC. [Nimbalkar] suggests ensuring that the data lines are correctly wired, and testing that the 5V and ground are connected properly. He then covered the connections with some hot glue to make it a little more robust since it’s about to see a lot of use.

Now all that’s needed is a quick press of the button to change which PC you are working on, streamlining what can be a tedious changeover — especially useful if you have a custom keyboard you want to use all the time.

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Amazon Dash Reboots Your Pi

We all know feature creep can be a problem in almost any project. A simple idea can often become unusable if a project’s scope isn’t clearly defined in the beginning. However, the opposite problem sometimes presents itself: forgetting to include a key feature. [Zach] had this problem when he built a Raspberry Pi magic mirror and forgot to build a physical reset/shutoff switch. Luckily he had a spare Amazon Dash button and re-purposed it for use with his Pi.

The Raspberry Pi doesn’t include its own on/off switch. Without installing one yourself, the only way to turn off the device (without access to the terminal) is to unplug it, which can easily corrupt data on the SD card. Since [Zach]’s mirror was already complete, he didn’t want to take the entire thing apart just to install a button. There’s already a whole host of applications for the Dash button, so with a little Node.js work on the Raspberry Pi he was able to configure a remote-reset button for his mirror.

This is a similar problem for most Raspberry Pi owners, so if you want to follow [Zach]’s work he has done a great job detailing his process on his project site. If you’re looking for other uses for these convenient network-enabled buttons, he also links to a Github site with lots of other projects. This pizza button is probably our favorite, though.

An ESP8266 in Every Light Switch and Outlet

[Hristo Borisov] shows us his clever home automation project, a nicely packaged WiFi switchable wall socket. The ESP8266 has continuously proven itself to be a home automation panacea. Since the ESP8266 is practically a given at this point, the bragging rights have switched over to the skill with which the solution is implemented. By that metric, [Hristo]’s solution is pretty dang nice.

esp8266-smart-lightswitchIt’s all based around a simple board. An encapsulated power supply converts the 220V offered by the Bulgarian power authorities into two rails of 3.3V and 5V respectively. The 3.3V is used for an ESP8266 whose primary concern is the control of a triac and an RGB LED. The 5V is optional if the user decides to add a shield that needs it. That’s right, your light switches will now have their own shields that decide the complexity of the device.

The core module seen to the right contains the actual board. All it needs is AC on one side and something to switch or control on the other The enclosure is not shown (only the lid with the shield connectors is seen) but can be printed in a form factor that includes a cord to plug into an outlet, or with a metal flange to attach to an electrical box in the wall. The modules that mate with the core are also nicely packaged in a 3D printed shield. For example, to convert a lamp to wireless control, you use a shield with a power socket on it. To convert a light switch, use the control module that has a box flange and then any number of custom switch and display shields can be hot swapped on it.

It’s all controllable from command line, webpage, and even an iOS app; all of it is available on his GitHub. We’d love to hear your take on safety, modularity, and overall system design. We think [Hristo] has built a better light switch!

Bamboo Plant Becomes A Stylish Light Switch

If flipping a regular old light switch or pressing buttons isn’t an adequately pleasing way to use your appliances around the house, how about poking at the leaves of a plant to turn on your lamp? [Xkitz] has provided a thorough breakdown of how to turn any conductive object in your living space into a nifty capacitive touch switch that adds a bit of charm to such an everyday action.

Creating an electrostatic field around a conductive medium, the capacitive touch relay constantly monitors this field and will toggle when any minuscule change to the capacitance is detected. [Xkitz] uses a bamboo plant as his trigger. Gently touching any leaf will still act as an adequate trigger — as cool demonstration of how the electrostatic field works.

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Interesting Switch Autopsy

We put a lot of trust into some amazingly cheap components, sometimes that trust is very undeserved. Long gone are the days when every electronic component was a beautifully constructed precision lab instrument.  As [Rupert Hirst] shows, this can be a hard lesson to learn for even the biggest companies.

[Rupert]’s Nexus 5 was suffering from a well known reboot issue. He traced it to the phone’s power switch. It was always shorting to ground, even though it clicked like it was supposed to.

He desoldered the switch and pried the delicate sheet metal casing apart. Inside were four components. A soft membrane with a hard nub on the bottom, presumably engineered to give the switch that quality feeling. Next were two metal buckles that produced the click and made contact with the circuit board, which is the final component.

He noticed something odd and  busted out his USB microscope. The company had placed a blob of solder on the bottom buckle. We think this is because steel on copper contact would lead to premature failure of the substrate, especially with the high impact involved during each switching event.

The fault lay in the imprecise placement of the solder blob. If it had been perfectly in the middle, and likely many phones that never showed the issue had it there, the issue would have never shown up. Since it was off-center, the impact of each switching event slowly deposited thin layers of solder onto the copper and fiberglass. Finally it built up enough to completely short the switch.

Interestingly, this exact problem shows up across different phone manufacturers, somewhere there’s a switch company with a killer sales team out there.

Physical Kill Switch For Rogue Applications

Necessity is the mother of invention, but sometimes frustration is as good a motivator. [Maciej] does a bunch of statistics in his day job using SPSS. silaczLike most complicated pieces of software, it can get hung, and the only way to stop it is to manually kill the running processes. Apparently, that happened one time too many for [Maciej].

He took matters into his own hands, repurposing a big red emergency-stop button for the task. It’s mounted on a jar, and the microcontroller inside is configured as a USB keyboard. When he mashes the button, it opens the “Run…” menu and types out taskkill spssengine.exe for him.

We can totally see the therapeutic value of such a device. Plus, in case SPSS is gobbling up his system memory and everything’s approaching standstill, the vital seconds saved by the microcontroller’s quick-typing fingers could be a lifesaver.