Metal Casting With Single Shelled PLA Masters

[3DTOPO] does a lot of metal casting (video link, embedded below). That’s obvious by the full and appropriate set of safety gear, a rarity on YouTube.

They had all the equipment to do it the normal way: craft or CNC out a master, produce a drag and a copy, make any necessary cores, and finally; pour the mold. This is a long and tedious process. It has a high rate of error, and there is a parting line.

Another set of methods are the lost ones. With these methods the master is produced out of a material like foam or wax. The master is surrounded by refractory and then melted, burned, or baked out of the mold. Finally the metal is poured in. Theoretically, a perfect reproduction is made without ever having to open the mold.
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[CNLohr]’s Glass PCB Fabrication Process

One of [CNLohr]’s bigger claims to fame is his process for making glass PCBs. They’re pretty much identical to regular, fiberglass-based PCBs, but [CNLohr] is building circuits on microscope slides. We’ve seen him build a glass PCB LED clock and a Linux Minecraft Ethernet thing, but until now, [CNLohr]’s process of building these glass PCBs hasn’t been covered in the depth required to duplicate these projects.

This last weekend, [CNLohr] put together a series of videos on how he turns tiny pieces of glass into functional circuits.

At the highest level of understanding, [CNLohr]’s glass PCBs really aren’t any different from traditional homebrew PCBs made on copper clad board. There’s a substrate, and a film of copper that is etched away to produce traces and circuits. The devil is in the details, and there are a lot of details for this build. Let’s dig deeper.

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Baby Monitor Rebuild is also ESP8266 Audio Streaming How-To

[Sven337]’s rebuild of a cheap and terrible baby monitor isn’t super visual, but it has so much more going on than it first seems. It’s also a how-to for streaming audio via UDP over WiFi with a pair of ESP8266 units, and includes a frank sharing of things that went wrong in the process and how they were addressed. [Sven337] even experimented with a couple of different methods for real-time compression of the transmitted audio data, for no other reason than the sake of doing things as well as they can reasonably be done without adding parts or spending extra money.

receiverThe original baby monitor had audio and video but was utterly useless for a number of reasons (French).  The range and quality were terrible, and the audio was full of static and interference that was just as loud as anything the microphone actually picked up from the room. The user is left with two choices: either have white noise constantly coming through the receiver, or be unable to hear your child because you turned the volume down to get rid of the constant static. Our favorite part is the VOX “feature”: if the baby is quiet, it turns off the receiver’s screen; it has no effect whatsoever on the audio! As icing on the cake, the analog 2.4GHz transmitter interferes with the household WiFi when it transmits – which is all the time, because it’s always-on.

Small wonder [Sven337] decided to go the DIY route. Instead of getting dumped in the trash, the unit got rebuilt almost from the ground-up.

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Learn Resin Casting Techniques: Cold Casting

Sometimes we need the look, feel, and weight of a metal part in a project, but not the metal itself. Maybe you’re going for that retro look. Maybe you’re restoring an old radio and you have one brass piece but not another. It’s possible to get a very metal like part without all of the expense and heat required in casting or the long hours in the metal fabrication shop.

Before investing in the materials for cold casting, it’s best to have practical expectations. A cold cast part will not take a high polish very well, but for brushed and satin it can be nearly indistinguishable from a cast part. The cold cast part will have a metal weight to it, but it clinks like ceramic. It will feel cool and transfers heat fairly well, but I don’t have numbers for you. Parts made with brass, copper, and iron dust will patina accordingly. If you want them to hold a bright shine they will need to be treated with shellac or an equivalent coating afterward; luckily the thermoset resins are usually pretty inert so any coating used on metal for the same purpose will do.

It is best to think of the material as behaving more or less like a glass filled nylon such as the kind used for the casing of a power tool. It will be stiff. It will flex a relatively short distance before crazing and then cracking at the stress points. It will be significantly stronger than a 3D printed part, weaker than a pure resin part, and depending on the metal; weaker than the metal it is meant to imitate.

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Tearing into Delta Sigma ADC’s

It’s not surprising that Analog to Digital Converters (ADC’s) now employ several techniques to accomplish higher speeds and resolutions than their simpler counterparts. Enter the Delta-Sigma (Δ∑) ADC which combines a couple of techniques including oversampling, noise shaping and digital filtering. That’s not to say that you need several chips to accomplish this, these days single chip Delta-Sigma ADCs and very small and available for a few dollars. Sometimes they are called Sigma-Delta (∑Δ) just to confuse things, a measure I applaud as there aren’t enough sources of confusion in the engineering world already.

I’m making this a two-parter. I will be talking about some theory and show the builds that demonstrate Delta-Sigma properties and when you might want to use them.

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What Could Go Wrong: SPI

Serial Peripheral Interface (SPI) is not really a protocol, but more of a general idea. It’s the bare-minimum way to transfer a lot of data between two chips as quickly as possible, and for that reason alone, it’s one of my favorites. But that doesn’t mean that everything is hugs and daffodils. Even despite SPI’s simplicity, there are still a few ways that things can go wrong.

In the previous article in this series, inspired by actual reader questions, I looked into troubleshooting asynchronous serial connections. Now that you’ve got that working, it’s time to step up to debugging your SPI bus! After a brief overview of the system, we’ll get into how to diagnose SPI, and how to fix it.

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How to Make a Custom LCD from Scratch

If you have ever wondered what it took to make your own custom graphic LCD from scratch, this video from [Applied Science] is worth a watch. It’s concise and to the point, while still telling you what you need to know should you be interested in rolling your own. There is also a related video which goes into much more detail about experimenting with LCD technology.

[Applied Science] used microscope slides and parts purchased online to make an LCD that displays a custom graphic when activated. The only step that home experimenters might have trouble following is coating the glass slides with a clear conductive layer, which in the video is done via a process called sputtering to deposit a thin film. You don’t need to do this yourself, though. Pre-coated glass is readily available online. (Search for Indium-Tin Oxide or ‘ITO’ coated glass.)

The LCD consists of a layer of liquid crystal suspended between two layers of conductive glass. An electrical field is used to change the orientation of crystals in the suspension, which modulate the light passing through them. Polarizing filters result in a sharp contrast and therefore a visible image. To show a particular shape, some of the conductive coating is removed from one of the layers in the shape of the desired image. The process [Applied Science] uses to do this is nearly identical to etching a custom PCB. Continue reading “How to Make a Custom LCD from Scratch”