Who Says Solder Paste Stencils Have To Be CNC Cut?

December 9, 2020 by Jenny List 19 Comments

Imagine having a surface mount kit that you’d like to stencil with solder paste and reflow solder, but which doesn’t come with a solder stencil. That was what faced [Honghong Lu], and she rose to the challenge by taking a piece of PET sheet cut from discarded packaging and hand-cutting her own stencil. It’s not a huge kit, the Technologia Incognita 2020 kit, but her home-made stencil still does an effective job.

So how does one create a solder stencil from household waste? In the video we’ve put below the break, she starts with her packaging, and cuts from it a square of PET sheet. It’s 0.24mm thick, which is ideal for the purpose. She then lays it over the PCB and marks all the pads with a marker pen, before cutting or drilling the holes for the pads. The underside is then sanded to remove protruding swarf, and the stencil can then be used in the normal way. She proves it by stenciling the solder paste, hand placing the parts, and reflowing the solder on a hotplate.

It’s clear that this is best suited to smaller numbers of larger components, and we’ll never use it to replace a laser-cut stencil for a thousand tiny 0201 discretes. But that’s not the point here, it’s an interesting technique for those less complex boards, and it’s something that can be tried by anyone who is curious to give stenciling and reflowing a go and who doesn’t have a project with a ready-cut stencil. And for that we like it.

Making your own stencils doesn’t have to include this rather basic method. They can be etched, or even 3D printed.

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This Automated Wire Prep Machine Cuts And Strips The Wire

December 9, 2020 by Dan Maloney 23 Comments

We’ve seen a fair number of automated wire cutting builds before, and with good reason: cutting lots of wires by hand is repetitive and carries the risk of injury. What’s common to all these automated wire cutters is a comment asking, “Yeah, but can you make it strip too?” As it turns out, yes you can.

The key to making this automated wire cutter and stripper is [Mr Innovative]’s choice of tooling, and accepting a simple compromise. (Video, embedded below.) Using just about the simplest wire strippers around — the kind with a diamond-shaped opening that adjusts to different wire gauges by how far the jaws are closed — makes it so that the tool can both cut and strip, and adapt to different wire sizes. The wire is fed from a spool to a custom attachment sitting atop a stepper motor, which looks very much like an extruder from a 3D-printer. The wire is fed through a stiff plastic tube into the jaws of the cutter. Choosing between cutting and stripping is a matter of aiming the wire for different areas on the cutter’s jaws, which is done with a hobby servo that bends the guide tube. The throw of the cutter is controlled by a stepper motor — partial closure nicks the insulation, while a full stroke cuts the wire off. The video below shows the build and the finished product in action.

Yes, the insulation bits at the end still need to be pinched off, but it’s a lot better than doing the whole job yourself. [Mr Innovative] has a knack for automating tedious manual tasks like this. Check out his label dispenser, a motor rotor maker, and thread bobbin winder.

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A UV Curing Wand For Everyone

December 6, 2020 by Matthew Carlson 12 Comments

The average person’s experience with an ultraviolet (UV) wand is getting a cavity at the dentist. However, anyone with a resin-based 3d printer knows how important a UV curing system is. Often times some spots on a print need a little bit of extra UV to firm up. [Mile] has set out to create an open-source UV curing wand named Photon that is cost-effective and easy to build.

What’s interesting here is that there are dozens if not hundreds of UV curing systems ranging from $5 LED flashlights to larger industrial flood systems. [Mile] dives right in and shows the trade-offs that those cheaper modules are making as well as what the commercial systems are doing that he isn’t. [Mile’s] Photon wand tries to be energy efficient with more irradiated power while staying at a lower cost. This is done by carefully selecting the CSP LEDs instead of traditional wire-bonded and making sure the light source is properly focused and cooled. From the clean PCB and slick case, it is quite clear that [Mile] has gone the extra step to make this production-friendly. Since there are two industry-standard wavelengths that resins cure at (364nm and 405nm), the LED modules in Photon are user-replaceable.

What we love about this project is looking past what is readily available and diving deep. First understanding the drawbacks and limitations of what is there, then setting a goal and pushing through to something different. This isn’t the first UV curing tool we’ve seen recently, so it seems there is a clear need for something better that’s what is out there today.

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Tiny Chain-Link Fence Made With Hand-Cranked Brilliance

December 6, 2020 by Danie Conradie 24 Comments

Chain link fences are woven with a mechanism that is almost hypnotic to watch, so [Levsha] decided to build his own tiny hand-crank tabletop version to make tiny copper wire fences.

Chain link consist of a series of wires bent and woven in a zigzag pattern. The zigzag bends are made by winding the wire around a rotating flat plate inside a stationary tube with a spiral slot in the side to keep the spacing of the bends consistent. [Levsha]’s version is roughly 1/10 scale of the real thing, and only does the bending and winding parts. Linking the bent wire together is up to the operator. All the components were machined on a lathe and CNC router, and beautifully finished and assembled on a wood base. The hardest part was the tube with the spiral slot, which took a few attempts to get right. [Levsha] initially tried to use steel wire, but it was too stiff and caused the winding mechanism to lock up. 0.4 mm copper wire turned out to be the best choice.

Although there is no practical use for this device that we can see, the craftsmanship is excellent, and it is one of those videos that reminds us how badly we want some machine tools.

Fine attention to detail is really what makes videos like this enjoyable to watch. Wee seen a few other such project, like a beautiful scratch-built lathe, or a pneumatic powered drone that can’t fly.

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Transforming Work Light Is More Than Meets The Eye

December 4, 2020 by Tom Nardi 3 Comments

While it does use the same M12 batteries, this impeccably engineered work light isn’t an official Milwaukee product. It’s the latest creation from [Chris Chimienti], who’s spent enough time in the garage and under the hood to know a thing or two about what makes a good work light. The modular design not only allows you to add or subtract LED panels as needed, but each section is able to rotate independently so it points exactly where you need it.

Magnets embedded in the 3D printed parts mean the light modules not only firmly attach to one another, but can be stuck to whatever you’re working on. Or you could just stack all the lights up vertically and use the rocket-inspired “landing legs” of the base module keep it vertical. Even if the light gets knocked around, the tension provided by rubber bands attached to each fold-out leg means it will resist falling over. In the video after the break [Chris] says the little nosecone on top is just for fun and you don’t have to print it, but we don’t see how you can possibly resist.

The same PCB is used on both ends of the light modules.

Of course, 3D printed parts and magnets don’t self-illuminate. The LED panels and switches are salvaged from cheap lights that [Chris] found locally for a few bucks, and a common voltage regulator board is used to step the 12 volts coming from the Milwaukee battery down to something the LEDs can use. He’s designed a very slick reversible PCB that’s used on either end of each light module to transfer power between them courtesy of semi-circular traces on one side and and matching pogo pins on the other.

As we saw in his recent Dremel 3D20 rebuild, [Chris] isn’t afraid to go all in during the design phase. The amount of CAD work that went into this project is astounding, and serves as fantastic example of the benefits to be had by designing the whole assembly at once rather than doing it piecemeal. It might take longer early on, but the final results really speak for themselves.

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Circuit VR: Squaring With Schmitt Triggers

December 4, 2020 by Al Williams 6 Comments

In the fantasy world of schematic diagrams, wires have no resistance and square waves have infinitely sharp rise times. The real world, of course, is much crueler. There are many things you can use to help tame the wild analog world into the digital realm. Switches need debouncing, signals need limiting, and you might even need a filter. One of the basic elements you might use is a Schmitt trigger. In

In this installment of Circuit VR, I’m looking inside practical circuits by building Schmitt triggers in the Falstad circuit simulator. You can click the links and get to a live simulation of the circuit so you can do your own experiments and virtual measurements.

Why Schmitt Triggers?

You usually use a Schmitt trigger to convert a noisy signal into a clean square digital logic level. Any sort of logic gate has a threshold. For a 5V part, the threshold might be that anything under 2.5V is a zero and at 2.5V or above, the signal counts as a one. Some logic families define other thresholds and may have areas where the signal is undefined, possibly causing unpredictable outputs.

There are myriad problems with the threshold, of course. Two parts might not have exactly the same threshold. The threshold might vary a bit for temperature or other factors. For parts with no forbidden zone, what happens if the voltage is right at the edge of the threshold?

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Exhaust Fan-Equipped Reflow Oven Cools PCBs Quickly

December 3, 2020 by Dan Maloney 6 Comments

With reflow soldering, sometimes close is good enough. At the end of the day, the home gamer really just needs a hot plate or an old toaster oven and a calibrated Mark I eyeball to get decent results. This exhaust fan-equipped reflow oven is an attempt to take control of what’s perhaps the more challenging part of the reflow thermal cycle — the cool down.

No fan of the seat-of-the-pants school of reflow soldering, [Nabil Tewolde] started with a cast-off toaster oven for what was hoped to be a more precise reflow oven. The requisite temperature sensors and solid-state relays were added, along with a Raspberry Pi Zero W and a small LCD display. Adding the cooling assist started by cutting a gaping hole cut in the rear wall of the oven, which was then filled with a short stretch of HVAC duct and a stepper-controlled damper. The far end of the duct was fitted with a PC cooling fan; while it seems sketchy to use a plastic fan to eject hot air from the oven, [Nabil] says the exhaust isn’t really that hot by the time it gets to the fan. At the end of the reflow phase of the thermal profile, the damper opens and the fan kicks on, rapidly cooling the oven’s interior.

Unfortunately, [Nabil] still needs to crack open the oven door to get decent airflow; seems like another damper to admit fresh air would help with that. That would complicate things a bit, but it still wouldn’t be as over-the-top as some reflow builds we’ve seen. Then again, that calibrated eyeball thing can work pretty well too, even without a toaster oven.

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