How to Build an Inverter, and Why Not to Bother

It’s ridiculously easy to lay hands on a cheap DC-to-AC inverter these days. They’re in just about every discount or variety store and let you magically plug in mains powered devices where no outlets exist. Need 120- or 240-VAC in your car? No problem – a little unit that plugs into the lighter socket is available for a few bucks.

So are these commodity items worth building yourself? Probably not as [GreatScott!] explains, but learning how they work and what their limitations are will probably help your designs. The cheapest and most common inverters have modified square wave outputs, which yield a waveform that’s good enough for most electronics and avoids the extra expense of producing a pure sinusoidal output. He explains that the waveform is just a square wave with a slight delay at the zero-crossing points to achieve the stepped pattern, and shows a simple H-bridge circuit to produce it. He chose to drive the output section with an Arduino, to easily produce the zero-crossing delay. He uses this low-voltage inverter to demonstrate how much more complicated the design needs to get to overcome the spikes caused by inductive loads and the lack of feedback from the output.

Bottom line: it’s nice to know how inverters work, but some things are better bought than built. That won’t stop people from building them, of course, and knowing what you’re doing in this field has been worth big bucks in the past.

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High Voltage Switching with MOSFETs

Using a MOSFET as a switch is generally pretty simple. Make the gate voltage sufficient with respect to the source and current flows through the channel. However, if you are switching higher voltages, you may need some additional circuitry to protect the device’s gate and possibly the microcontroller driving the whole thing, too. [Lewis] discusses high voltage switching in the latest in his series of videos dealing with MOSFETs. You can see the video below.

You’ll see in the video a breadboard setup driving a 50 V load and also a higher-voltage H-bridge. There are three major topics covered: Using an optoisolator, using a gate bleeder resistor, and using a zener diode to limit gate voltage.

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Dive Inside This Old Quartz Watch

In an age of smartwatches, an analog watch might seem a little old-fashioned. Whether it’s powered by springs or a battery, though, the machinery that spins those little hands is pretty fascinating. Trouble is, taking one apart usually doesn’t reveal too much about their tiny workings, unless you get up close and personal like with this microscopic tour of an analog watch.

This one might seem like a bit of a departure from [electronupdate]’s usual explorations of the dies within various chips, but fear not, for this watch has an electronic movement. The gross anatomy is simple: a battery, a coil for a tiny stepper motor, and the gears needed to rotate the hands. But the driver chip is where the action is. With some beautiful die shots, [electronupdate] walks us through the various areas of the chip – the oscillator, the 15-stage divider cascade that changes the 32.768 kHz signal to a 1 Hz pulse, and a remarkably tiny H-bridge for running the stepper. We found that last section particularly lovely, and always enjoy seeing the structures traced out. There are even some great tips about using GIMP for image processing. Check out the video after the break.

[electronupdate] knows his way around a die, and he’s a great silicon tour guide, whether it’s the guts of an SMT inductor or a Neopixel close-up. He’s also looking to improve his teardowns with a lapping machine, but there are a few problems with that one so far.

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Completely Scratch-Built Electronic Speed Controller

Driving a brushless motor requires a particular sequence. For the best result, you need to close the loop so your circuit can apply the right sequence at the right time. You can figure out the timing using a somewhat complex circuit and monitoring the electrical behavior of the motor coils. Or you can use sensors to detect the motor’s position. Many motors have the sensors built in and [Electronoobs] shows how to drive one of these motors in a recent video that you can watch below. If you want to know about using the motor’s coils as sensors, he did a video on that topic, earlier.

The motor in question was pulled from an optical drive and has three hall effect sensors onboard. Having these sensors simplifies the drive electronics considerably.

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Traction Control Gets More Power to the Road for Tot-Sized Lamborghini

We’ve all heard the complaints from oldsters: “Cars used to be so simple that all you needed to fix them was a couple of wrenches and a rag. Now, you need a computer science degree to even pop the hood!” It’s true to some extent, but such complexity is the cost of progress in the name of safety and efficiency. And now it seems this complexity is coming way down-market, with this traction control system for a Power Wheels Lamborghini.

While not exactly an entry-level model from the Power Wheels line of toddler transportation, the pint-sized Lamborghini Aventador [Jason] bought for his son had a few issues. Straight from the factory, its 6-volt drivetrain was a little anemic, with little of the neck-snapping acceleration characteristic of an electric drive. [Jason] opted to replace the existing 6-volt drive with a 12-volt motor and battery while keeping the original 6-volt controller in place. The resulting rat’s nest of relays was unsightly but sufficient to see a four-fold increase in top speed.

With all that raw power sent to only one wheel, though, the Lambo was prone to spinouts. [Jason] countered this with a traction control system using optical encoders on each of the rear wheels. A NodeMCU senses speed differences between the wheels and controls the motor through an H-bridge to limit slipping. As a bonus, a smartphone app can connect to the Node for in-flight telemetry. Check out the build and the car being put through its paces by the young [Mr. Steal Your Girl] in the video below.

The Power Wheels platform is infinitely hackable – from repairs to restorations to enhancements of questionable sanity, it seems like there’s nothing you can’t do with these little electric vehicles.

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A Stepper Motor for Two Dimensions

We’ve all heard linear motors, like those propelling Maglev trains, described as “unrolled” versions of regular electric motors. The analogy is apt and helps to understand how a linear motor works, but it begs the question: what if we could unroll the stator in two dimensions instead of just one?

That’s the idea behind [BetaChecker’s] two-axis stepper motor, which looks like it has a lot of potential for some interesting applications. Build details are sparse, but from what we can gather from the videos and the Hackaday.io post, [BetaChecker] has created a platen of 288 hand-wound copper coils, each of which can be selectively controlled through a large number of L293 H-bridge chips and an Arduino Mega. A variety of sleds, each with neodymium magnets in the base, can be applied to the platen, and depending on how the coils are energized, the sled can move in either dimension. For vertical applications, it looks like some coils are used to hold the sled to the platen while others are used to propel it. There are RGB LEDs inside the bore of each coil, although their function beyond zazzle is unclear.

We’d love more details to gauge where this is going, but with better resolution, something like this could make a great 3D-printer bed. If one-dimensional movement is enough for you, though, check out this linear stepper motor that works on a similar principle.

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My DIY BB-8: Problems, Solutions, Lessons Learned

Imagine trying to make a ball-shaped robot that rolls in any direction but with a head that stays on. When I saw the BB-8 droid doing just that in the first Star Wars: The Force Awakens trailer, it was an interesting engineering challenge that I couldn’t resist. All the details for how I made it would fill a book, so here are the highlights: the problems I ran into, how I solved them and what I learned.

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