Crossing Wheatstone Bridges

The Wheatstone bridge is a way of measuring resistance with great accuracy and despite having been invented over 150 years ago, it still finds plenty of use today. Even searching for it on Hackaday brings up its use in a number of hacks. It’s a fundamental experimental device, and you should know about it.

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Resistance in Motion: What You Should Know About Variable Resistors

Adjusting the volume dial on a sound system, sensing your finger position on a touch screen, and knowing when someone’s in the car are just a few examples of where you encounter variable resistors in everyday life. The ability to change resistance means the ability to interact, and that’s why variable resistance devices are found in so many things.

The principles are the same, but there are so many ways to split a volt. Let’s take a look at what goes into rotary pots, rheostats, membrane potentiometers, resistive touchscreens, force sensitive resistors, as well as flex and stretch sensors.

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Joysix, Six Degree of Freedom Mouse Made From Retractable Key Rings

[Nicolas Berger] submits his six degree of freedom mouse project. He hopes to do things like control a robot arm or fly an alien mothership.

We thought the construction was really neat; suspending a wooden ball in the middle of three retractable key rings. By moving the ball around you can control the motion of a cube displayed on the computer. We first thought this was done by encoders or potentiometers measuring the amount of string coming out of the key fobs. However, what’s actually happening is a little bit cleverer.

[Nicolas] has joined each string with its own 2 axis joystick from Adafruit. He had some issues with these at first because the potentiometers in the joysticks weren’t linear, but he replaced them with a different module and got the expected output. He takes the angle values from each string, and a Python program numerically translates the output from the mouse into something the computer likes. The code is available on his GitHub. A video of the completed mouse is after the break.

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Breadboards Go to Pot

Solderless breadboards are great for ICs and discrete components like resistors, capacitors, and transistors (at least the through hole kind). They aren’t so good at holding big components like potentiometers. Sure, you can jam trimmers in maybe. You can also solder leads to a pot, but that’s not pretty and tend to pull out when handled. [PaulStoffregen] got tired of it, so he put together some good looking PC boards that mount a 6mm shaft pot securely to a breadboard.

[Paul] noticed that having delicate or knobless adjustments on a breadboard inhibited people from playing with demo circuits. The new set up invites people to make adjustments. The pictures and video show an early version with six pins, but [Paul] added two more pins on the recent batch to increase the grip of the breadboard.

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Design in Package Flexibility into Your Next PCB

To err is human.  And to order the wrong component foot print is just part of engineering. It happens to us all; You’re working hard to finish a design, you have PCBs on the way and you’re putting in your order into your favorite parts supplier. It’s late, and you’re tired. You hit submit, and breathe a sigh of relief. Little do you know that in about a week when everything arrives, that you’ll have ordered the wrong component package for your design.

Well, fear not. [David Cook] has a solution that could save your bacon. He shows you how to design multiple footprints into your board to avoid the most common mistakes such as voltage regulators with different pin-outs than expected. Other uses for the trick include, common trim pots with different pin spacing and a layout for decoupling caps that will fit both a 0.1″ and 0.2″ footprints.

We’ll file this under the “Why Didn’t I Think of That” category. It’s a super simple hack, but that’s what we love about it. We could see this being very handy for people who often scavenge parts. Also, for makers that sell just a bare PCBs (without parts) to those that want just a board. No, it won’t save you if your need an SMD and you mistakenly ordered a dip, but at the end of the day, it’s a nice trick to keep up your sleeve.  You might never know when you’ll need it.

Arduino Synth Guitar Really Rocks

[Gr4yhound] has been rocking out on his recently completed synth guitar. The guitar was built mostly from scratch using an Arduino, some harvested drum pads, and some ribbon potentiometers. The video below shows that not only does it sound good, but [Gr4yhound] obviously knows how to play it.

The physical portion of the build consists of two main components. The body of the guitar is made from a chunk of pine that was routed out by [Gr4yhound’s] own home-made CNC. Three circles were routed out to make room for the harvested Yamaha drum pads, some wiring, and a joystick shield. The other main component is the guitar neck. This was actually a Squire Affinity Strat neck with the frets removed.

For the electronics, [Gr4yhound] has released a series of schematics on Imgur. Three SoftPot membrane potentiometers were added to the neck to simulate strings. This setup allows [Gr4yhound] to adjust the finger position after the note has already been started. This results in a sliding sound that you can’t easily emulate on a keyboard. The three drum pads act as touch sensors for each of the three strings. [Gr4yhound] is able to play each string simultaneously, forming harmonies.

The joystick shield allows [Gr4yhound] to add additional effects to the overall sound. In one of his demo videos you can see him using the joystick to add an effect. An Arduino Micro acts as the primary controller and transmits the musical notes as MIDI commands. [Gr4yhound] is using a commercial MIDI to USB converter in order to play the music on a computer. The converter also allows him to power the Arduino via USB, eliminating the need for batteries.

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Digitally Controlled Pot Taper

Those twisty knobs connected to potentiometers aren’t necessarily a strict linear progression from one resistance to another. Potentiometers have a taper. Yes, sometimes it’s a linear taper that’s a straight line from one resistance to another, but you can find log (audio) taper pots, and anti-log taper pots. It’s been this way for a hundred years, and now we have a pot with a digitally controllable taper thanks to a guitar pedal that fits in your shoe.

For the last few years, [John] has been hard at work creating the SoulPedal, a shoe insert that’s the wireless, wearable alternative to expression pedals, wah pedals, and every other guitar effects pedal that uses an ankle. [John] got the idea by replacing the light-sensitive resistor in a wah pedal with a force sensitive resistor in his shoe. It worked, but there were wires. Now the SoulPedal is based on a TI SoC +Radio with all the niceties you would expect.

When designing the ‘base station pedal’, [John] realized he had a digital pot with two channels, and the entire device only uses one of these channels. Instead of letting that little bit of silicon go to waste, [John] wired these two digital pots in parallel, allowing the user to customize the taper of a digital pot. If you’re asking yourself, ‘why’, the answer is, ‘because he could.’

It’s an interesting application for sure, and while this digitally controllable pot can replicate the linear, log, and anti-log tapers, the really interesting thing will be to see what non-standard tapers sound and feel like.