Building A Portable Solar Powered Spot Welder: Charging Supercapacitors

February 28, 2018 by Sean Boyce 48 Comments

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

January 5, 2018 by Sean Boyce 18 Comments

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.

Continue reading “Finding Your Motorbike Using Wi-Fi” →

Lunar New Year Is Coming, Shipping Times May Vary

January 3, 2018 by Sean Boyce 27 Comments

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.

Continue reading “Lunar New Year Is Coming, Shipping Times May Vary” →

Hunting Rogue Access Points With The ESP8266

December 28, 2017 by Sean Boyce 32 Comments

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.

Continue reading “Hunting Rogue Access Points With The ESP8266” →

Using Gmail With OAUTH2 In Linux And On An ESP8266

December 14, 2017 by Sean Boyce 21 Comments

One of the tasks I dread is configuring a web server to send email correctly via Gmail. The simplest way of sending emails is SMTP, and there are a number of scripts out there that provide a simple method to send mail that way with a minimum of configuration. There’s even PHP mail(), although it’s less than reliable.

Out of the box, Gmail requires OAUTH2 for authentication and to share user data, which has the major advantage of not requiring that you store your username and password in the application that requires access to your account. While they have an ‘allow less secure apps’ option that allows SMTP access for legacy products like Microsoft Outlook, it just doesn’t seem like the right way forward. Google documents how to interact with their API with OAUTH2, so why not just use that instead of putting my username and password in plaintext in a bunch of prototypes and test scripts?

Those are the thoughts that run through my head every time this comes up for a project, and each time I’ve somehow forgotten the steps to do it, also forgotten to write it down, and end up wasting quite a bit of time due to my own foolishness. As penance, I’ve decided to document the process and share it with all of you, and then also make it work on an ESP8266 board running the Arduino development environment.

Continue reading “Using Gmail With OAUTH2 In Linux And On An ESP8266” →

Statistics And Hacking: A Stout Little Distribution

December 13, 2017 by Sean Boyce 18 Comments

Previously, we discussed how to apply the most basic hypothesis test: the z-test. It requires a relatively large sample size, and might be appreciated less by hackers searching for truth on a tight budget of time and money.

As an alternative, we briefly mentioned the t-test. The basic procedure still applies: form hypotheses, sample data, check your assumptions, and perform the test. This time though, we’ll run the test with real data from IoT sensors, and programmatically rather than by hand.

The most important difference between the z-test and the t-test is that the t-test uses a different probability distribution. It is called the ‘t-distribution’, and is similar in principle to the normal distribution used by the z-test, but was developed by studying the properties of small sample sizes. The precise shape of the distribution depends on your sample size. Continue reading “Statistics And Hacking: A Stout Little Distribution” →

Statistics And Hacking: An Introduction To Hypothesis Testing

December 1, 2017 by Sean Boyce 20 Comments

In the early 20^th century, Guinness breweries in Dublin had a policy of hiring the best graduates from Oxford and Cambridge to improve their industrial processes. At the time, it was considered a trade secret that they were using statistical methods to improve their process and product.

One problem they were having was that the z-test (a commonly used test at the time) required large sample sizes, and sufficient data was often unavailable. By studying the properties of small sample sizes, William Sealy Gosset developed a statistical test that required fewer samples to produce a reasonable result. As the story goes though, chemists at Guinness were forbidden from publishing their findings.

So he did what many of us would do: realizing the finding was important to disseminate, he adopted a pseudonym (‘Student’) and published it. Even though we now know who developed the test, it’s still called “Student’s t-test” and it remains widely used across scientific disciplines.

It’s a cute little story of math, anonymity, and beer… but what can we do with it? As it turns out, it’s something we could probably all be using more often, given the number of Internet-connected sensors we’ve been playing with. Today our goal is to cover hypothesis testing and the basic z-test, as these are fundamental to understanding how the t-test works. We’ll return to the t-test soon — with real data. Continue reading “Statistics And Hacking: An Introduction To Hypothesis Testing” →