While the “M” in MIDI stands for “musical”, it’s possible to use this standard for other things as well. [s-ol] has been working on a VJ setup (mixing video instead of music) using various potentiometer-based hardware and MIDI to interface everything together. After becoming frustrated with drift in the potentiometers, he set out to outfit the entire rig with custom-built encoders.
[s-ol] designed the rotary-encoder based boards around an FPGA. It monitors the encoder for changes, controls eight RGB LEDs per knob, and even does capacitive touch sensing on the aluminum knob itself. The FPGA communicates via SPI with an Arduino master controller which communicates to a PC using a serial interface. This is [s-ol]’s first time diving into an FPGA project and it looks like he hit it out of the park!.
Even if you’re not mixing video or music, these encoders might be useful to any project where a standard analog potentiometer isn’t accurate or precise enough, or if you just need something that can dial into a specific value quickly. Potentiometers fall short in many different ways, but if you don’t want to replace them you might modify potentiometers to suit your purposes.
Continue reading “Upgrading A MIDI Controller With An FPGA”
[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.
Perhaps you’ve played a flight simulator before, using something like a mouse and keyboard. That’s a fine experience, but like any other activity you can get a lot more out of it if you put a little more effort into the experience. Some will upgrade to a joystick for a modest improvement, and others will build incredible accurate cockpit replicas down to the smallest detail. The builders of these “pits” are always looking for ways of improving their setups, and it’s from this world that we find a method of building specialized, inexpensive hall-effect sensors.
A hall-effect sensor is a circuit that outputs a voltage based on the presence of an external magnetic field. These can be used to make compasses, but with a permanent magnet in close proximity can also be used to create a potentiometer-like device at lower cost and with higher precision than a similarly-priced pot. There was a method of building these in the simulator world using the housing of a Bic pen and some strong glue, but [LocNar] has improved on this method as well. He repurposed some bearings and some stock metal tubing in order to fabricate a professional-level sensor at a fraction of the cost.
This build is essentially a solution for anyone needing a potentiometer that’s easier to build, less expensive, has higher precision, and interacts with a digital input in a much more predictable (and programmable) way. Certainly this has applications in the simulator world, but will work for many other applications. If you’ve never thought about the intricacies (and shortcomings) of potentiometers, some other folks have taken a deep dive into that as well.
Thanks to [Keith O] for the tip!
Potentiometers, or variable resistors, are a standard component that we take for granted. If it says “10k log” on a volume pot, than we fit and forget. But if like [Ben Holmes] you are modelling electronic music circuitry, some greater knowledge is required. To that end he’s created a rig for characterising a potentiometer to produce a look-up table of its values.
It’s a simple enough set-up in which a voltage controlled current source feeds the pot while an Arduino with a motor controller turns it through a stepper motor, and takes a voltage reading from its wiper via an analogue pin. Probably most readers could assemble it in a fairly short time. Where it becomes interesting though is in what it reveals about potentiometer construction.
Audio potentiometers are usually logarithmic. Which is to say that the rate of change of resistance is logarithmic over the length of the track, in an effort to mimic the logarithmic volume response of the human ear in for example a volume control. If you are taught about logarithmic pots the chances are you’re shown a nice smooth logarithmic curve, but as he finds out in the video below that isn’t the case. Instead they appear as a set of linear sections that approximate to a logarithmic curve, something that is probably easier to manufacture. It’s certainly useful to know that for [Ben]’s simulation work, but for the rest of us it’s a fascinating insight into potentiometer manufacture, and shows that we should never quite take everything for granted.
Continue reading “Characterising A Potentiometer With A Stepper Motor”
Whether with projects featured here or out in the real world, we have a tendency to focus most upon the end product. The car, solar panel, or even robot. But there’s a lot more going on behind the scenes that needs to be taken care of as well, whether it’s fuel infrastructure to keep the car running, a semiconductor manufacturer to create silicon wafers, or a control system for the robot. This project is one of the latter: a human interface device for a robot arm that is completely DIY.
While robots are often automated, some still need human input. The human input can be required all the time, or can be used to teach the robot initially how to perform a task which will then be automated. This “keyboard” of sorts built by [Ahmed] comes with a joystick, potentiometer, and four switch inputs that are all fully programmable via an Arduino Due. With that, you can perform virtually any action with whatever type of robot you need, and since it’s based on an Arduino it would also be easy to expand.
The video below and project page have all the instructions and bill of materials if you want to roll out your own. It’s a pretty straightforward project but one that might be worth checking out since we don’t often feature controllers for other things, although we do see them sometimes for controlling telescopes rather than robots.
Continue reading “A HID For Robots”
Here’s a rec-room ready hack: an automatic drink dispenser.
[truebassB]’s dispenser operates around a 555 timer, adjusted by a potentiometer. Push a button and a cup pours in a few seconds, or hold the other button to dispense as much as you want.
The dispenser is made from MDF and particle board glued together, with some LEDs and paper prints to spruce it up. Just don’t forget a small spill sink for any miscalculated pours. You needn’t fret over the internals either, as the parts are easily acquired: a pair of momentary switches, a 12V micro air pump, a brass nozzle, food-safe pvc tube, a custom 555 timing circuit — otherwise readily available online — a toggle switch, a power supply plug plus adapter and a 12V battery.
Continue reading “Push Button, Receive Beverage!”
Deep in the bowels of the Digikey and Mouser databases, you’ll find the coolest component ever. Motorized linear potentiometers are a rare, exotic, and just plain neat input device most commonly found on gigantic audio mixing boards and other equipment that costs as much as a car. They’re slider potentiometers with a trick up their sleeve: there’s a motor inside that can set the slider to any position.
The mechanical keyboard community has been pushing the boundaries of input devices for the last few years, and it looks like they just discovered motorized linear pots. [Jack] created a motorized sliding keycap for his keyboard. It’s like a scroll wheel, but for a keyboard. It’s beautiful, functional, and awesome.
The hardware for this build is just about what you would expect. A 60 mm motorized linear pot for the side-mount, or 100 mm mounted to the top of the keyboard, is controlled by an Arduino clone and a small motor driver. That’s just the hardware; the real trick here is the software. So far, [Jack] has implemented a plugin system, configuration software, and force feedback. Now, messing with the timeline in any Adobe product is easy and intuitive. This device also has a ‘not quite vibration’ mode for whenever [Jack] gets a notification on his desktop.
Right now, [Jack] is running a group buy for this in a reddit thread, with the cost somewhere between $55 and $75, depending on how many people want one. This is a really awesome product, and we can’t wait for Corsair to come out with a version sporting innumerable RGB LEDs. Until then, we’ll just have to drool over the video [Jack] posted below.
Continue reading “Wherein The Mechanical Keyboard Community Discovers Motorized Linear Potentiometers”