DIY Socket For Prosthetics Contains Power Supply, Charger

July 6, 2018 by Donald Papp 5 Comments

Innovation in prosthetics is open to anyone looking to enhance the quality of life, but there’s an aspect of it that is sometimes under-served. The DIY Prosthetic Socket entry to the Hackaday Prize is all about the foundation of a useful prosthesis: a custom, form-fitting, and effective socket with a useful interface for attaching other hardware. While [atharvshringaregt] is also involved with a project for a high-tech robotic hand with meaningful feedback, socket fitting and design is important enough to be its own project.

The goal is not just to explore creating these essential parts in a way that’s accessible and affordable to all, but to have them include a self-contained rechargeable power supply that can power attachments. Thoughtful strap placement and a power supply design that uses readily available components with a 3D printed battery housing makes this DIY prosthetic socket a useful piece of design that keeps in mind the importance of comfort and fitting when it comes to prosthetics; even the fanciest robot hand isn’t much good otherwise.

Circuit VR: Simple Buck Converters

July 6, 2018 by Al Williams 19 Comments

The first thing I ever built without a kit was a 5 V regulated power supply using the old LM309K. That’s a classic linear regulator like a 7805. While they are simple, they waste a lot of energy as heat, especially if the input voltage goes higher. While there are still applications where linear regulators make sense, they are increasingly being replaced by switching power supplies that are much more efficient. How do switchers work? Well, you buy a switching power supply IC, add an inductor and you are done. Class dismissed. Oh wait… while that might be the best way to do it from a cost perspective, you don’t really learn a lot that way.

In this installment of Circuit VR, we’ll look at a simple buck converter — that is a switching regulator that takes a higher voltage and produces a lower voltage. The first one won’t actually regulate, mind you, but we’ll add that in a future installment. As usual for Circuit VR, we’ll be simulating the designs using LT Spice.

Interestingly, LT Spice is made to design power supplies so it has a lot of Linear Technology parts in its library just for that purpose. However, we aren’t going to use anything more sophisticated than an op amp. For the first pass, we won’t even be using those.

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Wrangling RC Servos Becoming A Hassle? Try Serial Bus Servos!

July 5, 2018 by Roger Cheng 24 Comments

When we need actuators for a project, a servo from the remote-control hobby world is a popular solution. Though as the number of servos go up, keeping their wires neat and managing their control signals become a challenge. Once we start running more servos than we have fingers and toes, it’s worth considering the serial bus variety. Today we’ll go over what they are and examine three products on the market.

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These Capacitors Are A Cheap Gimmick

July 3, 2018 by Al Williams 31 Comments

If you search through an electrical engineering textbook, you probably aren’t going to find the phrase “gimmick capacitor” but every old ham radio operator knows about them. They come in handy when you need a very small capacitor of unknown value. For example, if you are trying to balance the stray capacitance in a circuit, you might not know exactly what value you need, but you know it won’t be very much. That’s when you want a gimmick capacitor.

A gimmick capacitor is made by taking two strands of insulated wire and twisting them together; the length and the tightness of the twist determine the capacitance. Tightening or loosening the twist, or trimming some of the wire off, makes it tunable.

These are most commonly found in RF equipment or high-speed logic because of the small capacitance involved — usually about 1 to 2 pF per inch of twist or so. The thicker the insulation, the less capacitance you’ll get, so it is common to use magnet wire or something else with a thin insulating layer. You can take this one step further and decrease the spacing by stripping down one wire as long as it isn’t going to touch anything else.

Obviously, the insulation needs to be good enough for the voltage on them, an important consideration in tube circuits, for instance. But other than that, a gimmick capacitor is a straightforward tool to have in your box of design tricks. Can we take this further? Continue reading “These Capacitors Are A Cheap Gimmick” →

Coolest Way To Watch 3D Printing: Lights, Camera, Octolapse!

July 2, 2018 by Tom Nardi 23 Comments

Octoprint is a household name for anyone into 3D printing and anyone regularly reading Hackaday. Described by creator Gina Häußge as “the snappy web interface for your 3D printer”, Octoprint allows you to control effectively any desktop 3D printer over the local network or Internet. It even has webcam support so you can watch your printer while it works, meaning you can finally put that video baby monitor back into the crib with Junior.

While the core functionality of Octoprint is fantastic alone, its true power is unlocked through the plugin system and the community that’s sprung up around it. With plugins, Octoprint can do everything from control RGB light strips in your printer’s enclosure to sending status messages via Discord. One particularly popular plugin that has been making the rounds lately is Octolapse by [FormerLurker]. This plugin provides a comprehensive intelligent system for creating time-lapse videos of prints.

What does that mean? Well, instead of simply taking a picture every few seconds like you’d do traditionally, Octolapse actually keeps track of the printer’s motions while its running. It can then take a picture at the opportune moment to create a number of user-selected effects. More importantly, it can even take control of the printer directly; moving the hotend away from the print before taking a picture. The effect is that the print simply “grows” out of the bed.

I thought it would be interesting to take a closer look at Octolapse and see just what it takes to create one of those awesome time-lapse videos. It turned out to be somewhat trickier than I anticipated, but the end results are so fantastic I’d say it’s a technique worth mastering.

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Move Aside Mercury: Measuring Temperature Accurately With An RTD

June 28, 2018 by Sean Boyce 40 Comments

Temperature is one of the most frequently measured physical quantities, and features prominently in many of our projects, from weather stations to 3D printers. Most commonly we’ll see thermistors, thermocouples, infrared sensors, or a dedicated IC used to measure temperature. It’s even possible to use only an ordinary diode, leading to some interesting techniques.

Often we only need to know the temperature within a degree Celsius or two, and any of these tools are fine. Until fairly recently, when we needed to know the temperature precisely, reliably, and over a wide range we used mercury thermometers. The devices themselves were marvels of instrumentation, but mercury is a hazardous substance, and since 2011 NIST will no longer calibrate mercury thermometers.

Luckily, resistance temperature detectors (RTDs) are an excellent alternative. These usually consist of very thin wires of pure platinum, and are identified by their resistance at 0 °C. For example, a Pt100 RTD has a resistance of 100 Ω at 0 °C.

An accuracy of +/- 0.15 °C at 0 °C is typical, but accuracies down to +/- 0.03 °C are available. The functional temperature range is typically quite high, with -70 °C to 200 °C being common, with some specialized probes working well over 900 °C.

It’s not uncommon for the lead wires on these probes to be a meter or more in length, and this can be a significant source of error. To account for this, you will see that RTD probes are sold in two, three, and four wire configurations. Two-wire configurations do not account for lead wire resistance, three-wire probes account for lead resistance but assume all lead wires have the same resistance, and four-wire configurations are most effective at eliminating this error.

In this article we’ll be using a 3-wire probe as it’s a good balance between cost, space, and accuracy. I found this detailed treatment of the differences between probe types useful in making this decision.

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Buttery Smooth Fades With The Power Of HSV

June 18, 2018 by Kerry Scharfglass 20 Comments

In firmware-land we usually refer to colors using RGB. This is intuitively pleasing with a little background on color theory and an understanding of how multicolor LEDs work. Most of the colorful LEDs we are use not actually a single diode. They are red, green, and blue diodes shoved together in tight quarters. (Though interestingly very high end LEDs use even more colors than that, but that’s a topic for another article.) When all three light up at once the emitted light munges together into a single color which your brain perceives. Appropriately the schematic symbol for an RGB LED without an onboard controller typically depicts three discrete LEDs all together. So it’s clear why representing an RGB LED in code as three individual values {R, G, B} makes sense. But binding our representation of color in firmware to the physical system we accidentally limit ourselves.

Last time we talked about color spaces, we learned about different ways to represent color spatially. The key insight was that these models called color spaces could be used to represent the same colors using different groups of values. And in fact that the grouped values themselves could be used to describe multidimensional spacial coordinates. But that post was missing the punchline. “So what if you can represent colors in a cylinder!” I hear you cry. “Why do I care?” Well, it turns out that using colorspace can make some common firmware tasks easier. Follow on to learn how!

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