Sense Home Energy Monitor: First Impressions

Sense has come up with a really interesting approach to home power monitoring. Their Sense Home Energy Monitor uses DSP and machine learning to “listen” to the power being consumed by your house, in real time, and with something like 15-20W resolution.

The box contents: The Sense unit, two magnetic loops, power harness, WiFi antenna, and some miscellaneous parts.

A small monitoring unit (the red box near the center of the picture above) is wired into both phases of a home power panel. Two sense loops are connected to the two main power phases coming into the panel, and a WiFi antenna is routed outside the panel.

Sense, installed in the electrical panel.

Setup was relatively straightforward, with just a few snags. Sense (no doubt on the advice of their lawyers) recommends turning off the main breaker if you do the installation yourself. They are also very careful to remind you, multiple times, that the leads to the main breaker are always live.

After the pickup are clamps attached (very easy), the WiFi antenna in place (not too hard) and the power wired in (straightforward, but a little tricky to get the wires to seat properly), the software setup can begin. Half a minute or so after powering Sense on, it chimes a short tune to let you know it’s up and running. (If you look closely, you can see amber LEDs flickering behind the plastic casing even before the chimes sound.)

Once installed and connected to your WiFi (stay nearby, since initial setup involves connecting to the unit via Bluetooth with a phone or tablet), Sense will start monitoring your home’s power consumption. Resolution is impressive — while I can’t confirm the fifteen-to-twenty watt periodic fluctuations in power, I can already see the 3D printer cycling the bed heater on and off.

Check out what it can see already. The small fluctuations are the 3D printer cycling the heated bed. The large, kilowatt-level ones are baseboard heaters. Being able to monitor those will really help!

A real-time graph of power consumption.

Sense’s real strength will come with time. Over time, it can learn what devices are in your home by sensing how they “sound” when they power on and off. Already, just from reading the graphs, I’ve learned that my computer monitor takes about 100w, the 3D printer perhaps 100-200W when active, and that baseboard heaters are HUGE power hogs, clocking in at about a kilowatt each.

But eventually, Sense should be able to name them and tell how long they’re on. According to the developers, it can sometimes even tell when devices aren’t working correctly — for instance, seeing a furnace cycle several times before igniting.

It’s not cheap at $299, but worth it. I bet it pays for itself before summer’s out.

Posted in Electronics, High Voltage, Power, Reviews, Tools, Toys | Tagged , , , , , | Leave a comment

Analog Mechanical Computing

Civilization advances by extending the number of important operations which we can perform without thinking about them.

–Alfred North Whitehead

It’s fascinating to see how far we’ve come in just a few decades. Check out this old US Navy film from 1953 on how a mechanical firing computer works. They’re using custom-cut gears and cams to physically calculate algebraic and trigonometric functions. People (okay, this is 1953 — “men”) enter data by turning wheels and moving levers, and mechanical linkages in a purpose-built computer the size of a refrigerator turn this into firing solutions.

These days, a microcontroller priced lower than a cheap cup of coffee could do all of this easily. A smartphone wouldn’t even notice the extra computational load, and could effortlessly handle a fleet’s worth of such computations while showing you the HD video of how it used to be done.

Posted in Analog, Mechanical, Nostalgia | Leave a comment

3D Printer Workflow

Hobbyist 3D printing is really picking up speed. With printers under $200 and approaching the magic $100 retail price — and pretty decent larger printers readily available in kit form for around $400 — it’s becoming much easier for schools, Makerspaces, and hobbyists to get started making stuff.

One question beginners might have is, what is involved in making something, from idea to thing? Once everything is up and working, it’s easier than you think. A few programs all work together to get the job done.

The process has three basic parts: Design, Slice, and Print. The best way to learn something like this is to either do it or at least watch it done, so let’s walk through the creation of a 3D printed object from idea to thing. (All of these steps can be nearly as simple or as complex as you like — it’s a very expandable, customizable hobby with something for just about anyone.)

The Design phase is done on CAD software — either a traditional visual CAD program like SolidWorks or Autodesk Inventor. I use SketchUp, since it’s free and easy to learn.

Suppose you want to make a thing. For instance, I could use a paper towel dispenser in the kitchen and probably upstairs bathrooms (to help with cleaning up after foster cats.)

One way is to look online to see if someone else has come up with a design you can simply slice and print. Thingiverse is a great place to start, even if their site scripting doesn’t always play nicely with Chrome. (When in doubt, hit ctrl-F5 to reload the page. This usually works for me.)

I found a few interesting designs, but nothing that really jumped out at me. So an alternative is to simply design your own. That’s the real beauty of a 3D printer: you can design something completely new, and fabricate it in the course of a few hours (even while you’re doing something else.)

The first step in the design is to get the specifications you need. In this case, measuring a full roll of paper towels is a good start. If that works, an empty one will work, too. Measuring a paper towel roll, I found that it was about 11″ long by 5″ wide, with a 1.5″ diameter center hole. (Normally, I do designs in metric, but if the target part is already specified in inches, that makes more sense here.)

So we need a 1.5″ diameter cylinder in the center (or maybe 1.4″ diameter to allow it to turn freely). It should be at least an inch or two long, and mounted to the wall in a way that will allow more than 2.5″ of clearance from the wall to the center of the roll. (I’ll use 3″ so it doesn’t scrape.) On the part near the wall, I’ll add holes for drywall screws, adapted from a previous design.

A first draft of (half of) a paper towel holder, ready to be sliced.

Next, the model needs to be sliced. This step involves turning the 3D model into actual print head movement commands that the 3D printer can understand. For this, the model is exported as an .STL file, which is just a list of the 3D triangles making up the surface of the object.

This .STL file is then imported into a slicing program. For now, we’ll use Cura — a popular freeware slicer with a nice GUI interface.

Several decisions need to be made prior to slicing, since this is the step where the specific manufacturing parameters are chosen. Specifically, we’ll go with:

  • 0.3mm (300 micron) layer height. This is basically “draft” quality, resulting in coarser layers, but more than adequate for a utilitarian part like this.
  • 1.2mm shell thickness. Since I’m using an 0.4mm nozzle size, this means that the slicer will use three outside layers in X/Y.
  • 1.2mm top and bottom layer thickness. Similarly to the shell thickness, this means that four top and bottom layers will be printed (since the layer height is 0.3mm.)
  • 25% infill. This controls how much of the internal volume is filled with plastic. Larger infill percentage makes for stronger parts — at least up to a point. 25% usually works well.
  • 190C hot end temperature. I’ve found this works well for the PLA filament I use.
  • 70C heated bed temperature, and
  • 40mm/sec printing speed

Once these settings are chosen, Cura will update the sliced model automatically. The next step is to save the resulting .gcode file to be sent to the printer.

The towel holder model is positioned on the printer plate and sliced, turning it into G-Code movement commands.

Finally, the .gcode file is sent to the printer. This can be done directly via SD card, but an easier option is to use OctoPrint — a 3D printer server with a nice GUI interface. When baked into the Raspberry Pi-specific OctoPi image, the result is almost a plug-and-play networked 3D printer.

The sliced parts, imported into OctoPrint.

At this point, assuming your printer is already leveled and calibrated, you can just load filament, hit Print, and wait for the parts to appear in a few hours.

The completed parts, ready for installation.

From design to completed project in an evening. That’s why they call it Rapid Prototyping!

Posted in 3D Printing, HOW-TO | Leave a comment

Non-Newtonian Motion…?

The EM drive, weird as it sounds, just keeps passing peer review. It’s starting to look like we’ve found something genuinely new here — an inertial drive! Until recently, that was considered science-fantasy by most — a way of changing velocity without “pushing” against something else.

In short, it throws Newton’s third law of motion out the window.

This copper frustum could end up being as famous as the first transistor.

It’s a very small effect — about 1.2 millinewtons per kilowatt, give or take ten percent or so. That’s a very subtle effect — one millinewton is about one twentieth of the force needed to lift a dime — but one that can be constantly applied over hours, days, weeks, months, or years, with no propellent needed.

If it works — if this effect is real — we’ll be able to build much more efficient (meaning faster, cheaper, and larger) long- and medium-distance spacecraft.

And if past technologies are any indication, the test model is probably terribly inefficient. Faraday’s first electric motor, after all, was just a wire spinning around in a mercury bath. From such humble beginnings, however, came all of our modern electric motor technology.

TL;DR (physics geeks): Don’t look now, but conservation of momentum might not be a thing, after all.

TL;DR (everyone else): If this works, we just got a LOT better at building spaceships. Not faster-than-light better (at least this year), but way, way better. Like go-to-Mars-for-the-week-someday better.

Posted in Current Events, Mad Science, Science | Leave a comment