An Optocoupler Doorbell Notifier

Over the years we’ve seen several attempts at adding Internet connectivity to the lowly wired doorbell. Generally, these projects aim to piggyback on the existing wiring, bells, and buttons rather than replace them entirely. Which invariably means at some point the AC wiring is going to need to interface with a DC microcontroller. This is often where things get interesting, as it seems everyone has a different idea on how best to bridge these two systems.

That’s the point where [Ben Brooks] found himself not so long ago. While researching the best way to tap into the 20 VAC pumping through his doorbells, he found a forum post where somebody was experimenting with optocouplers. As is unfortunately so often the case, the forum thread never really had a conclusion, and it wasn’t clear if the original poster ever figured it out.

DIY optocouplers wrapped in electrical tape

[Ben] liked the idea though, so he thought he would give it a shot. But before investing in real optocouplers, he created his own DIY versions to use as a proof of concept. He put a standard LED and photoresistor together with a bit of black tape, and connected the LED to the doorbell line with a resistor. Running the LED on 60 Hz AC meant it was flickering rapidly, but for the purposes of detecting if there was voltage on the line, it worked perfectly.

Wanting something slightly more professional for the final product, [Ben] eventually evolved his proof of concept to include a pair of 4N35s, a custom PCB, and a 3D printed enclosure. Powered by a Particle Xenon, the device uses IFTTT to fire off smartphone notifications and blink the lights in the house whenever somebody pushes the bell.

If you’re still wondering why it’s so tricky to connect a microcontroller up to your door bell, a quick look at some of the similar projects we’ve covered should give you a pretty good idea of how annoying these systems can be to modernize.

USB Power Delivery For All The Things

The promise of USB Power Delivery (USB-PD) is that we’ll eventually be able to power all our gadgets, at least the ones that draw less than 100 watts anyway, with just one adapter. Considering most of us are the proud owners of a box filled with assorted AC/DC adapters in all shapes and sizes, it’s certainly a very appealing prospect. But [Mansour Behabadi] hasn’t exactly been thrilled with the rate at which his sundry electronic devices have been jumping on the USB-PD bandwagon, so he decided to do something about it.

[Mansour] wanted a simple way to charge his laptop (and anything else he could think of) with USB-PD over USB-C, but none of the existing options on the market was quite what he wanted. He looked around and eventually discovered the STUSB4500, a a USB power delivery controller chip that can be configured over I2C.

With a bit of nonvolatile memory onboard, it can retain its settings so he didn’t have to include a microcontroller in his design: just program it once and it can be used stand-alone to negotiate the appropriate voltage and current requirements when its plugged in.

The board that [Mansour] came up with is a handy way of powering your projects via USB-C without having to reinvent the wheel. Using the PC configuration tool and an Arduino to talk to the STUSB4500 over I2C, the board can be configured to deliver from 5 to 20 VDC to whatever device you connect to it. The chip is even capable of storing three seperate Power Delivery Output (PDO) configurations at once, so you can give it multiple voltage and current ranges to try and negotiate for.

In the past we’ve seen a somewhat similar project that used USB-PD to charge lithium polymer batteries. It certainly isn’t happening overnight, but it looks like we’re finally starting to see some real movement towards making USB-C the standard.

DIY Clapper Lets You Pick Your Components

One thing that always means the end of the year is close is the reappearance of TV ads for “The Clapper.” After all, who needs home automation when you can clap on and clap off? While we’re partial to our usual home automation solutions, [Utsource123] shows us that building a clapper can be a fun and easy project using several similar circuits. One with a few transistors and another one with a 555 because, after all, what can’t a 555 do?

Of course, these circuits usually have a microphone. We were trying to think of how you could make a sound-sensitive element out of common parts. After all, you don’t care about the fidelity of the microphone pickup, just that it hears a loud noise. The circuits are about what you’d expect. The transistor version uses one to amplify the microphone and another to switch on the LED. You’d need a bit more to trigger a relay. The 555 uses an even simpler preamp transistor as a trigger.

While we aren’t bowled over with the idea of a clapper, we imagine these circuits aren’t far removed from the ones you buy in stores. For about $16 you also get enough switching to handle a simple AC load, though. Maybe Alexa and Google should allow making clapping a wake up word?

This is sure simpler than the last clapper clone we saw. Then there’s the deluxe DIY version.

Flux Gate Magnetometers Make A Special Current Probe

There are moments when current measurement is required on conductors that can’t be broken to insert a series resistor, nor encircled with a current transformer. These measurements require a completely non-invasive technique, and to satisfy that demand there are commercial magnetometer current probes. These probes are however not for the light of wallet, so [ensgoldmine] has created a much cheaper alternative.

The Texas Instruments GRV425 flux gate magnetometer integrated circuit on its TI evaluation module provides the  measuring element placed at the tip of a probe as close as possible to the conductor to be measured, with another GRV425 module at the head of the probe to measure ambient magnetic field for calibration purposes.  An Arduino Due measures and processes the readings, chosen due to its higher-resolution ADC than the more ubiquitous Arduino Uno.

The write-up is interesting even if you have no need for a current probe, because of its introduction to these sensing elements. Because it’s a rare first for Hackaday, we’ve never taken a close look at them before other than as an aside when talking about a scientific instrument on Mars.

Atomic Pi Gets A 3D-Printed Mac Makeover

The Atomic Pi is a pretty impressive piece of kit for the price, but it’s not exactly a turn-key kind of product. Even to a greater extent than what you might normally expect with a “dev” board like this, the user is responsible for putting together the rest of the pieces required to actually utilize it. But with this design by [Renri Nakano], you can turn the Atomic Pi into something that’s dangerously close to being a practical computer, and a trendy one at that.

Inspired by the 2019 Apple Mac Pro “Cheese Grater”, this 3D printable enclosure for the Atomic Pi is equal parts form and function. It integrates the necessary power supply to get things up and running without the need for the official breakout board or power module, which is good, since at the time of this writing they don’t seem to be available anyway. Plus it has a cool looking power button, so that’s got to count for something.

There’s also an integrated USB hub to give the Atomic Pi a bit more expandability, and a short HDMI extension cable that puts a video port on the back of the case. [Renri] even thought to leave an opening so you could run the wires for your wireless antennas.

At this point, we’ve seen several projects that mimic the unique case design of the 2019 Mac Pro. The level commitment ranges from recreating the design in CAD and milling it out of aluminum to just sticking a Raspberry Pi inside of a literal cheese grater from the kitchen. Naturally we enjoy a well executed Internet meme as much as the next hacker, but all the same, we were glad to see [Renri] put in the effort to make sure this case was more than just a pretty face.

[Thanks to baldpower for the tip.]

Everything You Wanted To Know About Padauk MCUs And More

At this point you’d need to have lived underneath a rock somewhere on the dark side of the Moon to not have heard about these amazing, 3-cent microcontrollers. A number of places have pitched in on them, but comprehensive reviews, let alone a full-blown review of the entire ecosystem surrounding these Padauk MCUs have been scarce. Fortunately, [Jay Carlson] has put in a lot of effort to collect everything you could possibly want to know about anything Padauk.

The most important take-away is that these MCUs do not have any kind of communication peripherals. UARTs, I2C, and SPI all have to be done in software. They’re not very great at low-power or battery-powered applications due to high power usage. Essentially you’ll be using GPIO pins a lot. On the other hand, its multi-CPU context, FPPA feature is rather interesting, with the article covering it in detail.

As for the development tools, [Jay] came away very impressed with the In-Circuit Emulation (ICE) instead of running code on an MCU, as this can reduce development times significantly. This makes even the OTP (one-time programmable) property of most Padauk MCUs less significant than one might at first assume.

Then there’s the actual programming of the MCUs. The Micro C compiler Padauk provides essentially implements a sub-set of the C language, with some macros to replace things like for loops. Initially this may seem like a weird limitation, until you realize that these MCUs have 64 to 256 bytes of SRAM. That’s bytes, without any prefixes.

Finally, [Jay] shows off a couple of test projects, including a NeoPixel SPI adapter and bike light, which are all available on Github. The WS2812b project is something we have seen before, for example this project from [Anders Nielsen] (featured in the article image), which provides another take on this range of MCUs.

Did reading [Jay]’s article change your mind on these Padauk parts? Have you used these MCUs and ICE parts before? Feel free to leave your thoughts in the comments.

The Ultimate Guide To Artisan USB Cables

If you’ve gone through the trouble of building your own customized mechanical keyboard, the last thing you want to do is plug it into your computer with some plebeian USB cable from the local electronics shop. Your productivity, nay livelihood, depends on all those 1s and 0s being reproduced with the crisp fidelity that’s only possible with a high-end USB cable. Anything less would be irresponsible.

Or at least, that’s what the advertising on the back of the package would say if we tried to sell the custom USB cables built by [Josef Adamčík]. But alas, he’s decided to give away all the details for free so that anyone can build their own delightfully overengineered USB cables. Do you need a paracord USB cable with GX12 aviation connectors in the middle? Of course not. But you still want one, don’t you?

As [Josef] admits in his blog post, there’s nothing particularly special about what he’s doing here. If you can splice wires together, you can build your own bespoke USB cables. But what attracted us to his write-up was the phenomenal detail he goes into. Every step is clearly explained and includes a nice, well-lit, photo to illustrate what he’s doing. Honestly, when the documentation for soldering some USB connectors onto a wire looks this good, there’s no excuse why more substantial projects get little more than a few blurry shots.

Of course, even for those of us who are no stranger to the ways of the soldering iron, there’s likely a few ideas you can pull from this project. We particularly liked his tip for taping the USB connector to the workbench while soldering it rather than trying to get it to stay in a vise, and his method for adding a coil the cable with a wooden jig and a heat gun is definitely something to file away for future use.

Then again in an era where even the lowly-USB cable can potentially be a security threat, or simply not live up to published specifications, rolling your own might not be such a bad idea.