A Simple Yet Feature-Packed Programmable DC Load

February 28, 2020 by 13 Comments

If you’ve got the hankering to own a lab full of high-end gear but your budget is groaning in protest, rolling your own test equipment can be a great option. Not everything the complete shop needs is appropriate for a DIY version, of course, but a programmable DC load like this one is certainly within reach of most hackers.

This build comes to us courtesy of [Scott M. Baker], who does his usual top-notch job of documenting everything. There’s a longish video below that covers everything from design to testing, while the link above is a more succinct version of events. Either way, you’ll get treated to a good description of the design basics, which is essentially an op-amp controlling the gate of a MOSFET in proportion to the voltage across a current sense resistor. The final circuit adds bells and whistles, primarily in the form of triple MOSFETS and a small DAC to control the set-point. The DAC is driven by a Raspberry Pi, which also supports either an LCD or VFD display, an ADC for reading the voltage across the sense resistor, and a web interface for controlling the load remotely. [Scott]’s testing revealed a few problems, like a small discrepancy in the actual amperage reading caused by the offset voltage of the op-amp. The MOSFETs also got a bit toasty under a full load of 100 W; a larger heatsink allows him to push the load to 200 W without releasing the smoke.

We always enjoy [Dr. Baker]’s projects, particularly for the insight they provide on design decisions. Whether you want to upgrade the controller for a 40-year-old game console or giving a voice to an RC2014, you should check out his stuff.

Continue reading “A Simple Yet Feature-Packed Programmable DC Load” →

Cheap Sensors And An SDR Monitor Conditions In This Filament Drying Farm

September 14, 2019 by 3 Comments

We don’t know where [Scott M. Baker] calls home, but it must be a pretty humid place indeed. After all, he has invested quite a bit in fancy vacuum storage containers to keep his 3D-printer filament dry, with the result being this sensor-laden filament drying farm.

[Scott] wasn’t content to just use these PrintDry containers without knowing what’s going on inside. After a little cleaning and lube to get all the containers working, he set about building the sensors. He settled on a wireless system, with each container getting a BME280 temperature/humidity/pressure sensor and an SYN115 315-MHz ISM band transmitter module. These go with an ATtiny85 into a compact 3D-printed case holding a little silica desiccant. The transmitters are programmed to comply with ISM-band regulations – no need to run afoul of those rules – while the receiver is just an SDR dongle and a Raspberry Pi running rtl_433. The long-ish video below details design and construction.

The idea behind these vacuum containers would seem to be to pull out humid air and prevent it from coming back in. But as [Scott] quickly learned from his telemetry, following the instructions results in the equivalent atmospheric pressure of only about 2700′ (823 meters) elevation – not exactly a hard vacuum. But as [Scott] points out, it’s enough to get a nice, tight seal, and his numbers show a lowered and constant relative humidity over time.

Continue reading “Cheap Sensors And An SDR Monitor Conditions In This Filament Drying Farm” →

Prusa Printer Gets An LCD-ectomy, Gains A VFD

June 12, 2019 by 17 Comments

What’s wrong with the OEM display on a Prusa I3 Mk3? Nothing at all. Then why replace the stock LCD with a vacuum fluorescent display? Because VFDs are much, much cooler than LCDs.

(Pedantic Editor’s Note: VFDs actually run a little warm.)

At least that’s the reasoning [Scott M. Baker] applied to his Prusa upgrade. We have to admit to a certain affection for all retro displays relying on the excitation of gasses. Nixies, Numitrons, and even the lowly neon pilot light all have a certain charm of their own, but by our reckoning the VFD leads the pack. [Scott] chose a high-quality Noritake 4×20 alphanumeric display module for his upgrade, thriftily watching eBay for bargains rather than buying from the big distributors. The module has a pinout that’s compatible with the OEM LCD, so replacing it is a snap. [Scott] simplified that further by buying a replacement Prusa control board with no display, to which he soldered the Noritake module. Back inside the bezel, the VFD is bright and crisp. We like the blue-green digits against the Prusa red-orange, but [Scott] has an orange filter on order for the VFD to make everything monochromatic. That’ll be a nice look too.

A completely none functional hack, to be sure, but sometimes aesthetics need attention too. And it’s possible that a display switch would help the colorblind use the UI better, like this oscilloscope mod aims to do.

Continue reading “Prusa Printer Gets An LCD-ectomy, Gains A VFD” →

Old Nixie Display Rides Again As 3D-Printer Filament Meter

May 9, 2019 by 9 Comments

We’re not sure about the name of this Nixie tube filament meter that [Scott M. Baker] built. He calls it a “filadometer”, perhaps a portmanteau of “filament” and “odometer”, in which case it makes sense. It may not flow trippingly from the tongue and we can’t come up with anything better, but whatever moniker you use it’s actually a pretty cool build.

The filadometer started life as something completely different and utterly typical for Nixie tube projects – a temperature and humidity gauge. [Scott] decided to recycle the eight-tube display to keep track of his Prusa, and in doing so he reveals a pretty remarkable degree of forethought in his design process. The original Nixie display has all the usual trappings – the driver chips, the shift registers, and the high voltage power supply. What stands out is the modularity of his design: the tube sockets and drivers live on a backplane PCB, with a Raspberry Pi and a separate HV supply board plugging into it. The original display had a Model B Pi, so there was plenty of room for a new Zero W. A new printed case and a little programming to capture the filament use from Octoprint is all it took to put this nifty little build back in action. The video below shows the details.

We’re always excited to see new videos from [Scott] because we learn so much from looking over his virtual shoulder. If you haven’t checked out his stuff, take a look at his homage to the 8″ floppy or his dual-port memory hack for retro gaming.

Continue reading “Old Nixie Display Rides Again As 3D-Printer Filament Meter” →

Well-Protected USB Power Strip Makes It Easy To Plug In

February 24, 2019 by 24 Comments

When we get a new device these days, somewhere in the package is likely to be a wall-wart USB power supply. We look for a place to plug in the little switch-mode dongle, rearrange a few plugs in the mains power strip, and curse its designers for the overly cozy outlet spacing. And all the while that USB-A plug on the power supply cable taunts us with its neat, compact form factor. If only there were a USB power strip.

Unwilling to suffer such indignity any longer, [Scott M. Baker] took matters into his own hands and designed this USB power distribution system. We were surprised to hear that he was unable to find a commercial USB power strip, but even if he had, it likely wouldn’t have had the bells and whistles that he added to his. The circuit went through a couple of revs, but each was focused on protection of the connected USB devices. He included both overcurrent protection, in the form of an electronic fuse built around a TPS2421 hot-swap controller, and overvoltage protection using a crowbar circuit with the usual zener-SCR arrangement. There’s also a transient voltage suppression diode to keep any inductive spikes at bay. Interestingly, each USB outlet has all these protections – it’s not just one protected bus feeding a bunch of USB outlets in parallel, but individual modules with all the circuitry. The modules are gangable and live inside a laser-cut acrylic case. The video below shows the design and build process in some detail.

We have to say that we always learn a lot about circuit design from [Scott]’s projects. You may recall his custom Atari 2600 controller or his dual-port memory retro game console, both interesting and instructive builds in their own right.

Continue reading “Well-Protected USB Power Strip Makes It Easy To Plug In” →

Using E-Paper Displays For An Electronic Etch A Sketch

November 9, 2018 by 12 Comments

Electronic things are often most successful when they duplicate some non-electronic thing. Most screens, then, are poor replacements for paper. Except, of course, for E-paper. These displays have high contrast even in sunlight and they hold their image even with no power. When [smbakeryt] was looking at his daughter’s Etch-a-Sketch, he decided duplicating its operation would be a great way to learn about these paper-like displays.

You can see a video of his results and his findings below. He bought several displays and shows them all, including some three-color units which add a single spot color. The one thing you’ll notice is the displays are slow which is probably why they haven’t taken over the world.

The displays connect to a Raspberry Pi and many of the displays are meant to mount directly to a Pi. The largest display is nearly six inches and some of the smaller displays are even flexible. It appears the three color displays were much slower than the ones that use two colors. To combat the slow update speeds, some of the displays can support partial refresh.

The drawing toy uses optical encoders connected to the Raspberry Pi. The Python code is available. Even if you don’t want to duplicate the toy, the comparison of the displays is worth watching. We were really hoping he’d included an accelerometer to erase it by shaking, but you’ll have to add that feature yourself. By the way, in the video, he mentions the real Etch-a-Sketch might work with magnets. It doesn’t. It is an aluminum powder that sticks to the plastic until a stylus rubs it off.

We’ve seen these displays many times before, of course. If you are patient enough, you can even use them as Linux displays.

Continue reading “Using E-Paper Displays For An Electronic Etch A Sketch” →

New Controller For Retro Console

October 12, 2018 by 4 Comments

In the world of retro gaming, when using emulators and non-native hardware it’s pretty common to use whatever USB controller happens to be available. This allows us to get a nostalgic look while using a  configurable controller. One thing that isn’t as common is using the original hardware while still finding a way to adapt a modern controller to an old console. This is exactly what you need though, when you’re retro gaming on a platform with notoriously terrible controllers.

[Scott] enjoys his Atari 5200 but the non-centering and generically terrible joystick wasn’t well received even in the early 80s when the console was in its prime. He decided that using a Dual Shock controller from a Playstation 2 would provide a much better gaming experience, and set about building an adapter. He found that in a way the Dual Shock controller was an almost perfect pairing for the Atari because it has two analog control sticks built-in already. There’s also an array of information on pairing the Dual Shock controller with AVR microcontrollers, so he wouldn’t have to reinvent the wheel. From there, it was just a matter of pairing communications protocols between the two pieces of hardware.

The project page goes into quite a bit of detail on SPI communication protocols and the needs of both the Atari and the Playstation controller. If you’re a retro gaming fan, really into communication protocols, or have always had a love-hate relationship with your Atari because the controllers were just that bad, it’s worth checking out. If this is too much, though, there are other ways to get that Atari nostalgia.

Thanks to [Baldpower] for the tip!

Continue reading “New Controller For Retro Console” →