Op Amp Challenge: An Ultra-Cheap PH Sensor Amplifier

May 2, 2023 by Jenny List 19 Comments

It’s rare in 2023 for an instrument to be entirely analog, instead it’s more normal for a front-end to feed the analog-to-digital converter (ADC) in a microcontroller. Typically the front-end will do the job of transforming whatever the output range of the sensor is, and present it to the microcontroller in whatever range it accepts. [David] had exactly this problem with a pH sensor, and rather than buy an expensive module to do the job he designed his own.

The sensor in question produces a relatively tiny voltage of -0.414 to +0.414 volts, and requires a very high input impedance. A FET input op-amp is selected, with the ground of the sensor shifted upwards into the positive range by a voltage divider. This then feeds a second op-amp that amplifies the resulting DC voltage for the microcontroller input.

This circuit is an especially simple op-amp application, and is a typical one for a sensor interface where a DC voltage needs to be brought into range of a microcontroller. If you’re not used to op-amp circuits then take a look, this type of analogue circuit is not difficult and might just save your butt some time.

Want to know more about simple op-amp circuits? Have we got the video for you!

Getting Ready For Act 2 Of The Great American Eclipse

May 2, 2023 by Dan Maloney 41 Comments

It seems like only yesterday that the “Great American Eclipse” swept from coast to coast, and for those who were lucky enough to watch it from along the path of totality, it was a true life experience. No natural phenomenon can compete with the beauty of a total solar eclipse, and if there’s one thing I heard more than anything else in those golden moments after the Sun returned from behind the Moon, it was, “When’s the next one?” Everyone wanted to do it again, and for good reason.

Back in 2017, that question was kind of rhetorical; everyone knew the next eclipse to cross the United States was a mere seven years off. For me personally, the passage of time has not dampened my enthusiasm for eclipses one bit, and I suspect the feeling is mutual among the many people who gazed in wonder and childlike glee at the celestial proceedings of 2017. But except for the very lucky who live within the path of totality, mounting an expedition that optimizes the viewing experience takes preparation. Now that we’re a little less than a year away for the next one, it’s time to get geared up and make plans for the 2024 eclipse.

Where and When?

The 2017 eclipse’s “Great American Eclipse” moniker was well earned, as the continental United States was the sole beneficiary of the view. This time around, the US isn’t the only country along the path; Mexico and Canada will also get in on the fun. In fact, Mexico may well be the best place to watch the eclipse from, but more on that later. Continue reading “Getting Ready For Act 2 Of The Great American Eclipse” →

An IN-12B Nixie tube on a compact driver PCB

Modern Components Enable Cheap And Compact Nixie Driver Circuit

May 2, 2023 by Robin Kearey 14 Comments

Nixie tubes can add some retro flair to any project, but they can also complicate your electronics quite a bit: after all, you need to generate a voltage high enough to ignite the tube and then switch that between ten separate display segments. Traditionalists may want to stick with chunky mains transformers and those unobtainium 74141 segment drivers, but modern components allow you to make things much more compact, not to mention way cheaper. [CNLohr] took this to an extreme, and used clever design tricks and his sharp online shopping skills to make an exceptionally compact Nixie driver circuit that costs less than $2.50.

That price doesn’t include the tubes themselves, but [CNLohr] nevertheless bought the cheapest Nixies he could find: a pair of IN-12B tubes that set him back just $20. He decided to generate the necessary 180 volts through a forward converter built around a $0.30 transformer and a three-cent MOSFET, controlled by software running on a CH32V003. This is one of those ultra-cheap microcontrollers that manage to squeeze a 48 MHz RISC-V core plus a bunch of peripherals into a tiny QFN package costing just 12 cents.

The existing toolchain to program these micros left a lot to be desired, so [CNLohr] wrote his own, called
ch32v003fun. He used this to implement all the control loops for the forward converter as well as PWM control of the display segments – a feature that adds a beautifully smooth turn-on and turn-off effect to the Nixie tubes. There’s still plenty of CPU capacity left to implement other features, although [CNLohr] isn’t sure what to put there yet. Turning the tubes into a clock would be an obvious choice, but the basic system is flexible enough to implement almost anything requiring a numeric display.

The compactness of this circuit is impressive, especially if you compare it to earlier solutions. There’s plenty of fun to be had with cheap-yet-powerful micros like the ch32v003, provided you can find them.

Continue reading “Modern Components Enable Cheap And Compact Nixie Driver Circuit” →

Machine Vision Automates Trainspotting With Unique Full-Length Portraits

May 2, 2023 by Dan Maloney 11 Comments

As hobbies go, trainspotting is just as valid a choice as any — we don’t judge. But it does present certain logistical challenges, such as having to be in visual range of a train to be able to spot it. There’s also the fact that trains are very large objects, and they tend to move very fast. What’s a railfan to do?

If you’re also technically minded, you might try building an automatic trainspotting bot like [jo-m] has. It looks like the hardware end of “Trainbot” is pretty simple since it has been tested on both x86 and Raspberry Pi, and supports both video4linux and Pi cam. The magic is in the software, which is able to detect a train entering the frame, record images, and then stitch them together into one long image. The whole thing is coded in Go and has some interesting bits, like a custom image patch mapping package.

Trainbot gives an unusual view of a train, one that most of us accustomed to watching a train pass at a crossing have never seen. By stitching small chunks of the train as it passes, Trainbot is able to show the entire train in a single image, which would be impossible to do except for being very, very far away from the track. [jo-m] also built a web interface for Trainbot where you can check out the comings and goings yourself. Each passing train’s image is accompanied by data like its velocity and acceleration, length of the train, and time of passage. There’s also a GIF of the original source video, which is pretty cool.

Here in the States, we don’t have a lot of passenger trains to spot, but we do have some really long freight trains. It’d be interesting to see how this works with a train that’s over a mile long; that would be quite an image. Looks like someone at least has the hardware in place to give it a try.

Recreating A Non-Standard USB Cable

May 1, 2023 by Jenny List 31 Comments

USB is a well-defined standard for which there are a reasonable array of connectors for product designers to use in whatever their application is. Which of course means that so many manufacturers have resorted to using proprietary connectors, probably to ensure that replacements are suitably overpriced. [Teaching Tech] had this problem with a fancy in-car video device, but rather than admit defeat with a missing cable, he decided to create his own replacement from scratch.

The plug in use was a multi-way round design probably chosen to match the harshness of the automotive environment. The first solution was to hook up a USB cable to a set of loose pins, but after a search to find the perfect-fitting set of pins a 3D printed housing was designed to replace the shell of the original. There’s an ouch moment in the video below the break as he receives a hot glue burn while assembling the final cable, but the result is a working and easy to use cable that allows access to all the device functions. Something to remember, next time you have a proprietary cable that’s gone missing.

Continue reading “Recreating A Non-Standard USB Cable” →

ESA’s Jupiter-bound Probe Hits Antenna Snag

May 1, 2023 by Tom Nardi 27 Comments

While the few minutes it takes for a spacecraft’s booster rocket to claw its way out of Earth’s gravity well might be the most obviously hazardous period of the mission, an incredible number of things still need to go right before anyone on the ground can truly relax. Space is about as unforgiving an environment as you can imagine, and once your carefully designed vehicle is on its way out to the black, there’s not a whole lot you can do to help it along if things don’t go according to plan.

That’s precisely where the European Space Agency (ESA) currently finds themselves with their Jupiter Icy Moons Explorer (Juice) spacecraft. The April 14th launch from the Guiana Space Centre went off without a hitch, but when the probe’s 16 meter (52 foot) radar antenna was commanded to unfurl, something got jammed up. Judging by the images taken from onboard cameras, the antenna has only extended to roughly 1/3rd its total length.

The going theory is that one of the release pins has gotten stuck somewhere, preventing the antenna from moving any further. If that’s the case, it could mean jiggling the pin a few millimeters would get them back in the game. Unfortunately, there’s no gremlins with little hammers stowed away in the craft, so engineers on the ground will have to get a little more creative. Continue reading “ESA’s Jupiter-bound Probe Hits Antenna Snag” →

Squeeze Over A Minute Of Movie Filming Onto A 35mm Still Cartridge

May 1, 2023 by Jenny List 14 Comments

There’s an allure to shooting film in the digital age which isn’t quite satisfied by digital filters for your smartphone camera. Aside from the technical challenge of working with a medium limited in sensitivity compared to its electronic replacement there are aesthetic reasons for wanting to shoot with particular lenses not found on any modern cameras. Sadly though, movie film in formats such as Super 8 is expensive to buy and even more expensive to develop.

It’s a problem [Blaž Semprimožnik] addressed with his Okto 35 camera, a unique design that fits a minute and 7 seconds of 8mm-like movie filming onto a much cheaper roll of 35mm still camera film. How does it achieve this feat? By splitting the width of the film into four parallel tracks of 8mm-sized frames.

The camera is a 3D printed design, with all mechanical functions performed by stepper motors to avoid the complex gear trains that would have been found in cameras from the home movie heyday. Each frame advance is a single sprocket hole on the 35mm film, and the track selection is performed automatically by moving the C-mount lens assembly sideways.

The result is a camera which is definitely unconventional, but which delivers something very close to that 8mm experience at a much lower cost per frame. There’s no reflex viewfinder or through-the-lens light metering, but since this is a camera likely to be used by enthusiasts rather than by 1970s consumers we’re guessing this won’t be a problem for most users.

There doesn’t appear to be anything in the way of downloadable STL files or other resources, probably because there’s a possibility he might put the camera into limited production. For the amount of work that he’s evidently put in we wish him luck, and given that the bench on which this is being written has more than one 8mm camera on it, we’re even slightly tempted by one. You might be too, after you’ve watched the video below the break.

This is a novel approach to a 35mm movie camera for still film cartridges, but it’s by no means the first. Previous ones we’ve seen have been full-frame designs though, capturing only a few seconds per roll.

Continue reading “Squeeze Over A Minute Of Movie Filming Onto A 35mm Still Cartridge” →