Storm Detector Modules: Dancing in the Rain

Earlier, we had covered setting up an AS3935 lightning detector module. This detector picks up radio emissions, then analyzes them to determine if they are a lightning strike or some other radio source. After collecting some data, it outputs the estimated distance to the incoming storm front.

But that only gets you halfway there. The device detects many non-lightning events, and the bare circuit board is lacking in pizzazz. Today I fix that by digging into the detector’s datasheet, and taking a quick trip to the dollar store buy a suitable housing. The result? A plastic plant that dances when it’s going to rain!
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An Introduction to Storm Detector Modules

Lightning storm detectors have been around for a surprisingly long time. The early designs consisted of a pair of metal bells and a pendulum. When there was a charge applied, for example by connecting one bell to the ground and the other to a lightning rod, the bells would ring when a lightning storm was close by. In the mid 18th century, these devices were only practical for demonstration and research purposes, but very likely represent the earliest devices that convert electrostatic charge to mechanical force. A bit over a hundred years later, the first lightning detector was considered by some as the first radio receiver as well.

As soon as I found out about storm detector chips, I knew I would have to get one working. For about $25, I ordered an AMS AS3935 module from China. This chip has been featured before in a number of excellent projects such as Twittering lightning detectors, and networks of Sub-Saharan weather stations. While there’s an Arduino library for interfacing with this IC, I’m going to be connecting it up to an ESP8266 running the NodeMCU firware, which means digging into the datasheet and writing some SPI code. If any of the above tickles your fancy, read on! Continue reading “An Introduction to Storm Detector Modules”

Building a Portable Solar-Powered Spot Welder: Nearly Practical!

Last time, we covered storing and charging a 3000 Farad supercapacitor to build a solar-powered, portable spot welder. Since then, I’ve made some improvements to the charging circuit and gotten it running. To recap, the charger uses a DC-DC buck converter to convert a range of DC voltages down to 2.6 V. It can supply a maximum of 5 A though, and the supercapacitor will draw more than that if allowed to.

Capacitor charge current decreases with time as the capacitor charges. Source: Hyperphysics

After some failed attempts, I had solved that by passing the buck converter output through a salvaged power MOSFET. A spare NodeMCU module provided pulse width modulated output that switched the MOSFET on for controlled periods of time to limit the charging current. That was fine, but a constant-voltage charger really isn’t the right way to load up a capacitor. Because the capacitor plates build up a voltage as it charges, the current output from a constant-voltage charger is high initially, but drops to a very low rate in the end.

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Building a Portable Solar Powered Spot Welder: Charging Supercapacitors

Before Lunar New Year, I had ordered two 3000 F, 2.7 V supercapacitors from China for about $4 each. I don’t actually remember why, but they arrived (unexpectedly) just before the holiday.

Supercapacitors (often called ultracapacitors) fill a niche somewhere between rechargeable lithium cells and ordinary capacitors. Ordinary capacitors have a low energy density, but a high power density: they can store and release energy very quickly. Lithium cells store a lot of energy, but charge and discharge at a comparatively low rate. By weight, supercapacitors store on the order of ten times less energy than lithium cells, and can deliver something like ten times lower power than capacitors.

Overall they’re an odd technology. Despite enthusiastic news coverage, they are a poor replacement for batteries or capacitors, but their long lifespan and moderate energy and power density make them suitable for some neat applications in their own right. Notably, they’re used in energy harvesting, regenerative braking, to extend the life of or replace automotive lead-acid batteries, and to retain data in some types of memory. You’re not likely to power your laptop with supercapacitors.

Anyway, I had a week-long holiday, and two large capacitors of dubious origin. Sometimes we live in the best of all possible worlds. Continue reading “Building a Portable Solar Powered Spot Welder: Charging Supercapacitors”

Finding Your Motorbike Using Wi-Fi

An urban planner once told me that every car requires at least four times as much space as they actually occupy. Each needs a spot on the roads, and three available parking spaces: one at home, one at work, and one to shop. Motorcycles are much smaller, but they still spend most of their time parked.

Motorcycles are the primary means of transport in Southeast Asia, and learning to safely drive one is an essential part of adapting to life here. Assuming it’s not pouring rain and you’re not flooded past your ankles, it’s actually quite a pleasant experience… until you have to park.

Unlike the parking lots you may be familiar with, there’s no expectation that your bike won’t be moved. In fact, it might very well end up on another floor, in another parking lot, or behind hundreds of impassable parked bikes on the roof. In the latter case, the attendant will shrug and suggest you come back in a few hours. Eventually, this won’t even register as a frustration – you will simply reason that there are plenty of other things that are more convenient here, like the weather (recent typhoon aside) or unlimited symmetrical fiber to the home for USD 5 a month.

That being said, with a little technology the problem could be lessened a bit while waiting for automated parking lots to become commonplace. On rare occasions I see people with little radio emitters that make their headlights flash, but they’re not terribly common here and require carrying yet another thing on my already full key chain (homes here typically use several different locks). It seemed pretty easy to pull off something similar using my smart phone with an ESP8266 running NodeMCU. I had been meaning to try out the sleep modes to save battery power anyway, so off I went.

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Lunar New Year is Coming, Shipping Times May Vary

With one holiday period coming to a close, another looms on the horizon: Lunar New Year. That means three things in my mind: nice weather, a beautiful holiday with great food, and that I had better get all my orders for electronic parts for the next few months out immediately. In fact, I should have done it last month but I’m a bit closer to the source than many of you are.

In any case, Lunar New Year affects our ability to order neat gadgets at a time of year when some of us have received a little money to spend. So I thought I’d take a moment away from hacking to share with you how important this holiday is to much of the world so we can manage our expectations for quick global shipping accordingly.

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Hunting Rogue Access Points with the ESP8266

Cantennas outperform every consumer-grade Wi-Fi antenna I’ve had the bad luck of purchasing. Cantenna is a mashup of ‘can’ and ‘antenna’ creating the nickname for a directional waveguide antenna built from re-purposed steel cans. For anyone who has yet to build one, it makes an excellent afternoon project. Here are some build instructions and technical details. I went beyond that, and ended up catching a rogue WiFi access point in the process.

When I needed to extend the range of some ESP8266-based sensors, cantennas were right at the top of my list of things to try. It was easy enough to build one, attach it to a Wemos Mini D1 Pro, and call the job done… leaving me with plenty of time to over-engineer it, and I ended up down a bit of a rabbit hole.

The first thing I did was stop using cans. Canned goods are not only expensive in my corner of the world, but more importantly don’t lend themselves that well to making a standardized antenna in volume. I can also only eat so many beans! The latter reason alone is enough to consider an alternative design like a modular dish reflector.

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