Finally, A Differently Useless Machine

Traditionally, the useless machine is a simple one that invites passersby to switch it on. When they do, the machine somehow, some way, turns itself off; usually with a finger or finger-like object that comes out from the box in what feels like an annoyed fashion. Honestly, that’s probably part of what drives people to turn them on over and over again.

But [Bart Blankendaal] has managed to turn the useless machine on its head. When this machine is switched to the on position, unseen forces inside the box will spin the toggle switch around 180° to the off position.

What’s really happening is that an Arduino is getting a signal from the toggle switch, and is then rotating it on a ball bearing with a stepper motor driven through an H-bridge.

It shouldn’t be too hard to make one of these yourself, given that [Bart] has provided the schematic and STLs. If we weren’t living in such touchy times, we might suggest building one of these into your Halloween candy distribution scheme somehow. Sell the switch as one that turns on a candy dispenser, and then actually dispense it after three or five tries.

Many see useless machines as tangible examples of existential quandary. Here is one that takes that sentiment a bit further by snuffing out a candle.

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Abused Hard Drive Becomes POV Clock

We all know that there’s not much to do with an old hard drive. Once you render the platters unreadable and perhaps harvest those powerful magnets, there’s not much left of interest. Unless, of course, you turn the whole thing into a persistence-of-vision clock.

At least that’s what [Leo] did when he created “PendoLux”. The clock itself is pretty simple; like any POV project, it just requires a way to move an array of flashing LEDs back and forth rapidly enough that they can trick the eye into seeing a solid image. [Leo] put the read head mechanism of an old HDD into use for that, after stripping the platters and motor out of it first.

The voice coil and magnet of the head arm are left intact, while a 3D-printed arm carrying seven RGB LEDs replaces the old heads. [Leo] added a small spring to return the arm to a neutral position, and used an Arduino to drive the coil and flash the LEDs. Getting the timing just right was a matter of trial and error; he also needed to eschew the standard LED libraries because of his heavy use of interrupts and used direct addressing instead.

POV clocks may have dropped out of style lately — this hard drive POV clock and a CD-ROM version were posted years ago. But [Leo]’s clock is pretty good looking even for a work in progress, so maybe the style will be making a comeback.

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Build Your Own Grid Tie Inverter

Inverters that convert DC into AC are pretty commonplace, some cars even have standard AC receptacles in them for you to plug in your favorite appliance. However, there’s a particular type of inverter called a grid tie inverter that allows you not only to make AC, but also inject it back through an AC outlet to power other devices in conjunction with the normal AC service. Why? Maybe you want to use your own generator or solar power. In some cases, the power company will pay you if you produce more power than you consume. Maybe you just want to know you can do it. That seems to be the motivation behind [fotherby’s] build, which is quite substantial.

The setup only handles about 60 watts, but it does all the functions you need: DC to AC conversion as well as phase and voltage matching. Actually, just converting DC to AC is almost trivial if you don’t care about the waveform. But in this case, you do care that you can create an AC signal to match the one already on the line.

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FET Based Motor Driver Is Better Than L298N

If you want to build a small robot with a motor, you are likely to reach for an L298N to interface your microcontroller to the motor, probably in an H-bridge configuration. [Dronebot] has used L298N chips like this many times. In the video below, he uses a TB6612FNG instead, taking advantage of the device’s use of MOSFETs. The TB6612 may be a little more expensive, but it’s clearly worth it.

You can get breakout boards for the tiny chips. [DroneBot] looks at several ready-to-go breakout boards. They are not drop-in compatible, though. For example, the L298N can operate motors from 4.5 to 46V while the TB6612 can go from 2.5 to 13.5V on the motor voltage. The L298N also handles more current. However, because of its relatively low efficiency, it needs a heat sink. The TB6612 boasts up to 95% efficiency and also has a low current standby mode. Of course, the TB6612 drops much less voltage which is great if you are using low voltage motor.

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Stepper-Controlled Chop Saw Automates A Tedious Job

We’re not going to question why [Absorber Of Light] needs to cut a bazillion little fragments of aluminum stock. We assume his reasoning is sound, so all we’re interested in is the automated chop saw he built to make the job less tedious, and potentially less finger-choppy.

There are probably many ways to go about this job, but  [Absorber] leaves few clues as to why he chose this particular setup. Whatever the reason, the build looks like fun, with a long, stepper-driven threaded rod pushing a follower down a track to a standard chop saw. The aluminum stock rides in the track and gets pushed out a set amount before being lopped off cleanly as the running saw is lowered by a linear actuator. The cycle then repeats until the stock is gone.

An Arduino controls the stock-advance stepper in the usual way, but the control method for the linear actuator is somewhat unconventional. A second stepper motor has two cams offset by 180° on the shaft. The cams actuate four microswitches which are set up in an H-bridge configuration. The stepper swivels back and forth to run the linear actuator first in one direction then the other, with a neutral position in between. It’s an interesting approach using mechanical rather than the typical optical isolation. Check it out in action in the video below.

We’ll admit to some curiosity as to the use of the coupons this rig produces, so maybe we’ll get lucky with some details from [Absorber Of Light] in the comment section. After all, we knew exactly what the brass tubes being cut by the similar “Auto Mega Cut-O-Matic”  were being used for.

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Split Flap Clock Keeps Time Thanks To Custom Frequency Converter

Why would anyone put as much effort into resurrecting a 1970s split-flap clock as [mitxela] did when he built this custom PLL frequency converter? We’re not sure, but we do like the results.

The clock is a recreation of the prop from the classic 1993 film, Groundhog Day, rigged to play nothing but “I Got You Babe” using the usual sound boards and such. But the interesting part was getting the clock mechanism keeping decent time. Sourced from the US, the clock wanted 120 VAC at 60 Hz rather than the 240 VAC, 50 Hz UK standard. The voltage difference could be easily handled, but the frequency mismatch left the clock running unacceptably slow.

That’s when [mitxela] went all in and designed a custom circuit to convert the 50 Hz mains to 60 Hz. What’s more, he decided to lock his synthesized waveform to the supply current, to take advantage of the long-term frequency control power producers are known for. The write-up goes into great detail about the design of the phase-locked loop (PLL), which uses an ATtiny85 to monitor the rising edge of the mains supply and generate the PWM signal that results in six cycles out for every five cycles in. The result is that the clock keeps decent time now, and he learned a little something too.

If the name [mitxela] seems familiar, it’s probably because we’ve featured many of his awesome builds before. From ludicrous-scale soldering to a thermal printer Polaroid to a Morse-to-USB keyboard, he’s always got something cool going on.

Electromechanical YouTube Sub Counter Trades Clicks For Clacks

Acquiring a new YouTube subscriber is a blessed event that deserves far more fanfare than a phone notification. But maybe blinkenlights don’t really do it for you anymore, or you simply prefer to be soothed sonically rather than visually. Well, what could be more satisfying than the crisp clack of an electromechanical 7-segment display? Six of them, of course. These things look great, they sound great, and once they’re set, they don’t need power to stay that way.

These displays switch between black and white by reversing current flow through their electromagnets, so [Zack] turned to the H-bridge in order to use them with DC. One H-bridge for each segment of six displays adds up fast, though. To get around this, [Zack] tied one pole of each electromagnet together for a common signal input, and used the other pole to control each segment individually. Then, he was able to tie all the A segments together, all the B segments, and so on, and only needs 13 H-bridges to do it all.

There was just one thing [Zack] didn’t count on. Once he got the board soldered up and running, the displays started acting funny. The low impedance of the coils was causing them to influence each other over the common path, so he added diode arrays to keep them in line.

[Zack]’s using an ESP32 to get the 411 through the Google API, and four octal serial switches to drive the displays. Even more satisfying than all those clacks is the displays’ operational economy baked into [Zack]’s code—as they count up, any segments common to the first digit and the next digit remain on. Increment your way past the break to check out the build video.

Not focused on numbers, but still want to celebrate each new sub? Try a dancing robot or a Tetris twist.

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