Switching Over To SMPS For Efficiency

August 11, 2019 by Bryan Cockfield 30 Comments

[Hesam Moshiri] has built a variable switch-mode power supply over on hackaday.io. When prototyping a new circuit, often the goal is to get a proof-of-concept working as soon as possible to iron out all of the bugs it might have. The power supply can easily be an afterthought, and for smaller projects we might just reach for an adjustable LM317 voltage regulator to dial in the correct voltage and then move on with the meat of the project. These linear regulators are incredibly inefficient though, so if you find yourself prototyping with one of these often enough, it might be worthwhile to switch to something better.

While it’s easy to simply buy a switch-mode power supply (SMPS) that has everything you need, and rated for 90% or higher efficiency at the same time, getting one with an adjustable output isn’t as easy. This one is based on the relatively popular LM2576-Adj chip which handles the switching frequency part of the circuit automatically. You will also need some large capacitors, an inductor (one of the disadvantages of an SMPS circuit) and a small potentiometer to use as the feedback control for the LM2576. This special pin allows the output voltage of the SMPS to be precisely controlled.

Granted, this project might not be breaking any new grounds, but if you’ve never given serious thought to your small breadboard circuit power supplies, it’s definitely worth looking into. An improvement from a linear regulator’s 30% efficiency to 90% efficiency from an SMPS will not only save you a ton of energy but also solve a lot of heat dissipation problems. If you don’t want to build a switch-mode supply 100% from scratch, though, it might also be possible to modify an existing one to suit your needs as well.

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” →

Spoiler Alert! Repairing A Race Car Can Get Complicated, Fast.

August 28, 2017 by James Hobson 37 Comments

[Big Fish Motorsports] has a vehicle with an adjustable rear spoiler system that broke in the lead up to a big race. The original builder had since gone AWOL so the considerable talents of [Quinn Dunki] were brought to bear in getting it working again.

Cracking open the black control box of mystery revealed an Arduino, a ProtoShield and the first major road block: the Arduino remained stubbornly incommunicado despite several different methods of trying to read the source code. Turns out the Arduino’s ATMega324 was configured to be unreadable or simply fried, but an ATMega128 [Quinn] had proved to be a capable replacement. However, without knowing how the ten relays for this spoiler system were configured — and the race day deadline looming ever larger — [Quinn] opted to scrap the original and hack together something of her own design with what she had on hand.

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An Adjustable Sit/Stand Desk For Under $100

January 23, 2015 by Rick Osgood 33 Comments

[Cornel Masson] is a 46-year-old computer programmer. He’s been working on his computer for the last 30 years. Computer work can be good for the wallet but it can be bad for our health, particularly the neck and back. You can purchase adjustable desks to allow you to change positions from sitting to standing, but unfortunately these desks are often expensive. [Cornel] took matters into his own hands and build his own adjustable riser for under $100.

To start, [Cornel] used a typical computer desk. He didn’t want to build the entire thing from scratch. Instead he focused on building a riser that sits on top of the desk, allowing him to change the height of both the monitor and keyboard. His design used mostly wood, aluminum stock, threaded rods, and drawer slides.

The main component is the monitor stand and riser. The riser is able to slide up and down thanks to four drawer slides mounted vertically. [Cornel] wanted his monitor to move up and down with ease, which meant he needed some kind of counter weight. He ended up using a gas strut from the trunk of a Nissan, which acts as a sort of spring. The way in which it is mounted makes for a very close approximation of his monitor’s weight. The result is a monitor that can be raised or lowered very easily. The stand also includes a locking mechanism to keep it secured in the top position.

The keyboard stand is also mounted to drawer slides, only these are in the horizontal position. When the monitor is lowered for sitting, the keyboard tray is removed from the keyboard stand. The stand can then be pushed backwards, overlapping the monitor stand and taking up much less space. The keyboard stand has small rollers underneath to help with the sliding. The video below contains a slideshow of images that do a great job explaining how it all works.

Of course if replacing the entire desk is an option go nuts.

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Print Your Own Adjustable Lenses

March 6, 2013 by Mike Szczys 23 Comments

[Christopher] is really going the distance with his liquid-filled 3D printed lens project. The idea is to create a bladder out of two pieces of clear plastic. It can then be filled with liquid at a variable level of pressure to curve the plastic and create an adjustable lens. He was inspired by the TED talk (which we swear we already covered but couldn’t find the post) given by [Josh Silver] on adjustable eyeglass lenses.

Don’t miss the video after the break. [Christopher] shows off the assembly process for one lens. Two 3D printed frames are pressure fit together to hold one piece of plastic wrap. Two of those assemblies are then joined with JB weld and some 3D printed clips that help to hold it. A piece of shrink tubing is used as a hose to connect a syringe to the bladder. By filling the lens assembly with water he’s able to adjust how it refracts light.

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