Check Soil Moisture At A Glance With This Useful Display

June 18, 2021 by Zoe Skyforest 6 Comments

Keeping soil moist is key to keeping most plants happy. It can be a pain having to dip one’s fingers into dirty soil on the regular, so it’s desirable to have a tool to do the job instead. [Andrew Lamchenko] built a capable soil moisture monitor, and equipped it with an E-ink display for easy readings at a glance.

The device is built around the NRF52810 or other related NRF52 microcontrollers, which run the show. Rather than using an off-the-shelf sensor to determine soil conditions, an LMC555CMX timer chip is used, a variant of the classic 555 timer designed for low power consumption. Combined with the right PCB design, this can act as a moisture sensor by detecting capacitance changes in the soil. The sensor is also able to send data using the MySensor protocol, allowing it to be used as a part of a home automation system.

The soil is tested periodically with the moisture sensor, and displayed on the attached e-ink screen. Since the e-ink display requires no electricity except when rewriting the display, this allows the sensor to operate for long periods without using a lot of battery power. The soil can be checked, the display updated, and then the entire system can be put to sleep, using tiny amounts of power until it’s time to test the soil again.

It’s a great example of design for low power applications, where component selection really is everything. We’ve featured [Andrew]’s projects before; he’s long been a fan of using e-ink displays to create long-lasting, low power budget sensor platforms. Video after the break.

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Just How Water Resistant Is The Casio F91W?

June 18, 2021 by Zoe Skyforest 25 Comments

Water resistance is an important feature of a modern watch. It makes wearing the watch far more practical in this modern world of sudden rainstorms and urban water balloon ambushes. The Casio F91W, one of the company’s most popular watches, is claimed to be water resistant to “30 meters”, which in ISO parlance, means it is suitable for splashes and rain resistance only. [Rostislav Persion] wanted to get a better idea of what this really meant, so set about investigating for himself.

The first step was to simply immerse the watch under 5.5″ of cold tap water while pressing the buttons and observing for any signs of water ingress. Already, the watch proved it is far more than just rain resistant, so [Rotislav] decided to disassemble the watch and learn how it achieved this.

Disassembly revealed that the watch’s case was entirely sealed, except for three buttons. The buttons, however, are specially designed in order to seal with the plastic case of the watch. Each button consists of a stainless steel pin, machined to be larger on the outside-facing side than the inside. The buttons also have a rubber O-ring seal to allow them to move in the case without allowing water to leak inside. [Rotislav] then compares the simple design to buttons used on watches with higher water resistance ratings, which boast multiple O-ring seals and more complex designs.

Given [Rotislav’s] results, we’d be far more confident getting our affordable Casio watches a little wet. Obviously, we wouldn’t expect to make a warranty claim if damage occurred from use outside the specs, but it’s clear the watch is far more capable than standards might suggest. If that’s not enough though, you can always set about modifying the watch to improve its water resistance even further.

LED Matrix Glasses Built With The Help Of Graph Paper

June 18, 2021 by Zoe Skyforest 5 Comments

These days, there’s all manner of addressable LEDs out there that can be easily used to produce blinky, flashy projects. However, there’s nothing stopping makers from doing things the old fashioned way, and hacking together an matrix out of raw LEDs. [Deepak Khatri] did just that with his own custom build.

Rather than rely on a PCB or other substrate to hold the matrix together, [Deepak] elected to freeform the design instead. A matrix of holes was cut in a cardboard template with the aid of graph paper. LEDs were then inserted into the holes in the requisite pattern, and their own leads soldered together to create the frame for the glasses. Additional wires that were needed were then installed, doubling as a bridge to allow the glasses to rest comfortably on the nose. Black epoxy was then used on the back side to block the light from blinding the wearer. The matrix is controlled by a pair of shift registers addressed by a microcontroller, and the display animates impressively smoothly.

it’s a fun build, and one that we suspect looks particularly impressive at night. They’d also make it easy for your friends to spot you in a dark club. We’ve seen some impressively stylish LED glasses over the years, too, dating all the way back to [macetech]’s pair from 2012. Video after the break.

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Blowing A 5000 A Fuse Takes Some Doing

June 18, 2021 by Zoe Skyforest 37 Comments

Fuses are generally there to stop excessive electrical currents from damaging equipment or people’s soft, fleshy bodies when faults occur. However, some people like to blow them just for fun, and [Photonicinduction] is just one of those people. He recently decided to push the boat out, setting his mind to the task of popping a 5000 A fuse in his own back yard. (Video, embedded below.)

The fuse looks quite haggard after the event

It’s not a job for the faint-hearted. The fuse is rated at 5,000 A — that’s the nominal rating for the currents at which it is intended to operate. Based on the datasheet, the part in question is capable of withstanding 30,000 A for up to five full seconds. To pop the fuse instantly takes something in the realm of 200,000 A.

To achieve this mighty current, a capacitor bank was built to dump a huge amount of energy through the fuse. Built out of ten individual capacitor units wired up in parallel, the total bank comes in at 10,000 μF, and is capable of delivering 200,000 A at 3000 V. (Just not for very long.) The bank was switched into circuit with the fuse via a pneumatic switch rated at just 12,000 A.

The results are ferocious, with both the fuse and switch contacts blasting out hot metal and flashes of light when the power is dumped. It’s a heck of a display. We’ve featured big capacitor banks before too, though they pale in comparison to what we’ve seen here today.

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Upgrading The PowerBook 100 With A Fresh New Battery

June 17, 2021 by Zoe Skyforest 13 Comments

The PowerBook 100 was one of the earliest Apple laptops released, coming not long after the breakout Macintosh Portable. Unlike modern hardware, it relied on sealed lead acid batteries. [360alaska] has such a laptop whose original battery is long dead, so they set about building a replacement battery with lithium cells instead.

The battery and its associated support circuitry is a mite unconventional in its design, but it gets the job done. The build uses two lithium polymer pouch cells in place of the original four cell sealed-lead acid battery, to replicate the roughly 7.2V nominal voltage. Because of this, unfortunately the stock PowerBook charger can’t provide enough voltage to fully charge the LiPo cells up to their full 8.4 volts.

The workaround selected is that when the batteries fall below 80% state of charge, relays disconnect the cells from their series configuration powering the laptop, and instead connect each cell to its own single-cell charger board. Once charging is complete, the relays switch back out of charging mode so the batteries power the laptop once more. The only major drawback is that withdrawing the power adapter while the batteries are on charge will cut all power to the laptop.

It may not be perfect, but [360alaska] has succeeded in building a drop-in battery solution for the PowerBook 100 that can be used with the stock charger. Laptop batteries can be a fraught thing to deal with; often there are safeguards or DRM-type issues to navigate to get them to work around. Sometimes open-source designs are the best solution out there.

A Tidy Octave Mod For The Casio SK-1

June 17, 2021 by Zoe Skyforest 5 Comments

1985 saw the release of the Casio SK-1, a compact sampling keyboard that brought the technology to a lower price point than ever before. However, one drawback of this was that it comes stock with only a 2.5 octave keyboard. [Jonas Karlsson] wanted a little more range out of the instrument, so set about hacking in his own octave mod.

The build consists of fiddling with the SK-1’s microprocessor clock to change the pitch of the notes generated by the instrument. The original clock is generated by a simple LC circuit, which in this mod is fed to an inverter, and then a pair of flip-flops to divide the clock by four. The original clock and the divided version are then both sent to a mux chip. With the flick of the switch, either the original or downshifted clock can be sent to the microprocessor.

With the slower clock feeding the microprocessor, all the notes are downshifted an octave. The resulting sound, which you can listen to on Soundcloud, is similar to what you get when chopping down sample rates. It bears noting, however, that as this mod changes the master clock, other features such as rhythms are also effected.

It’s a great mod which gives the instrument a gloomier, grittier sound on demand. The Casio SK-1 has long been prized for its hackability; we’ve seen them completely worked over in previous mods. If you’ve got your own twisted audio experiments cooking up in the workshop, be sure to drop us a line.

How To Get Into Cars: Land Speed Racing

June 17, 2021 by Zoe Skyforest 12 Comments

Land speed racing is one of the oldest forms of motorsport, and quite literally consists of going very, very fast in (ideally) a straight line. The higher the speed your car can attain, the better! It’s about the pure pursuit of top speed above all else, and building a car to compete is a calling for a dedicated few. If you’d like to join them, here’s how to go about it.

Faster, Faster, Faster!

A great example of the “36HP” Volkswagen class, which challenges competitors to set land speed records using only classic VW engines, with categories for various levels of modification. Note the aero wheels and raked stance. Credit: Utah Salt Flats Racing Association

While taking the outright land speed record typically requires a jet-engined sled of singular design, there is plenty of land speed competition to be had in various classes for competitors fielding their own entries. There are vintage classes for older technology engines, still popular from the dawn of hotrodding, like Ford Flathead V8s and other contemporary motors. There are also classes split by engine displacement, number of cylinders, aerodynamic modifications, or the type of fuel used.

Racers often pick a record or set of records they wish to beat – for example, wanting to set the the fastest speed for a gasoline-powered, naturally-aspirated four cylinder – and build their car to that end. Alternatively, a racer might build a car with a large V8 engine, for example, to compete in one class, and then disable several cylinders on a later run to try and snatch records in lower classes as well. Continue reading “How To Get Into Cars: Land Speed Racing” →