Conductive Concrete Confounds Circuitry

There’s a fairly good chance you’ve never tried to embed electronics into a chunk of concrete. Truth be told, before this one arrived to us via the tip line, the thought had never even occurred to us. After all, the conditions electronic components would have to endure during the pouring and curing process sound like a perfect storm of terrible: wet, alkaline, and with a bunch of pulverized minerals thrown in for good measure.

But as it turns out, the biggest issue with embedding electronics into concrete is something that most people aren’t even aware of: concrete is conductive. Not very conductive, mind you, but enough to cause problems. This is exactly where [Adam Kumpf] of Makefast Workshop found himself while working on a concrete enclosure for a color-changing barometer called LightNudge.

While putting a printed circuit board in the concrete was clearly not workable, [Adam] was hoping to simplify manufacturing of the device by embedding the DC power jack and capacitive touch sensor into the concrete itself. Unfortunately, [Adam] found that there was a resistance of about 200k Ohm between the touch sensor and the power jack; more than enough to mess with the sensitive measurements required for the touch sensor to function.

Even worse, the resistance of the concrete was found to change over time as the curing process continued, which can stretch out for weeks. With no reliable way to calibrate out the concrete’s internal conductivity, [Adam] needed a way to isolate his electronic components from the concrete itself.

Through trial and error, [Adam] eventually found a cheap method: dipping his sensor pad and wire into an acrylic enamel coating from the hardware store. It takes 24 hours to fully cure, and two coats to be sure no metal is exposed, but at least it’s an easy fix.

While the tip about concrete’s latent conductivity is interesting enough on its own, [Adam] also gives plenty of information about casting concrete parts which may be a useful bit of knowledge to store away for later. We have to admit, the final result is certainly much slicker than we would have expected.

This is the first one we’ve come across that’s embedded in concrete, but we’ve got no shortage of other capacitive touch projects if you’d like to get inspired.

Pumpkin Piano Promises a Gourd Time

Fall – it’s that time of year that brings falling leaves, Hallowe’en, and a pumpkin version of everything that you hold dear. In this case, it’s not a latte – it’s [Robert Vorthman]’s Pumpkin Piano.

[Robert] took a straightforward approach to the build, pressing a Raspberry Pi into service as the backbone of the operation. This is combined with an Adafruit breakout board for the MPR121, which is a chip that provides 12 capacitive touch-sensitive inputs. These are connected to the bountiful produce which make up the piano keys in this fun holiday hack. [Robert] uses some Python code that talks to fluidsynth, a software synthesizer that uses Soundfont files to create different sounds. It’s all wrapped up with some Neopixels that flash when each vegetable is triggered.

The build would make a great party piece for just about any fall gathering, and [Robert] has done a great job of rolling up all the hardware and software required in the write-up. For another take on a vegetable-based orchestra, check out last year’s Harpsi-gourd.

Hacking Touch Screens to Count Pulses

Heart rate sensors available for DIY use employ photoplethysmography which illuminates the skin and measures changes in light absorption. These sensors are cheap, however, the circuitry required to interface them to other devices is not. [Petteri Hyvärinen] is successfully investigating the use of capacitive touchscreens for heart rate sensing among other applications.

The capacitive sensor layer on modern-day devices has a grid of elements to detect touch. Typically there is an interfacing IC that translates the detected touches into filtered digital numbers that can be used by higher level applications. [optisimon] first figured out a way to obtain the raw data from a touch screen. [Petteri Hyvärinen] takes the next step by using a Python script to detect time variations in the data obtained. The refresh rate of the FT5x06 interface is adequate and the data is sent via an Arduino in 35-second chunks to the PC over a UART. The variations in the signal are very small, however, by averaging and then using the autocorrelation function, the signal was positively identified as a pulse.

A number of applications could benefit from this technique if the result can be replicated on other devices. Older devices could possibly be recycled to become low-cost medical equipment at a fraction of the cost. There is also the IoT side of things where the heart-rate response to media such as news, social media and videos could be used to classify content.

Check out our take on the original hack for capacitive touch imaging as well as using a piezoelectric sensor for the same application.

Controlling a Moog Werkstatt with a Capacitive Touch Jankó Keyboard

[Ben Bradley], a member of Freeside Atlanta, built a capacitive touch Jankó keyboard for the Georgia Tech Moog Hackathon. Jankó Keyboards are a 19th-Century attempt to add a more compact piano keyboard. There are three times as many keys as a traditional piano but arranged vertically for (supposedly) greater convenience while playing–an entire octave can be covered with one hand. But yeah, it never caught on.

[Ben]’s project consists of a series of brass plates wired to capacitive touch breakout boards from Adafruit, one for each of the Arduino Mega clone’s four I2C addresses. When a key is touched, the Arduino sends a key down signal to the Werkstatt while using a R-2R ladder to generate voltage for the VCO exponential input.

The most recent Moog Hackathon was the third.  Twenty-five teams competed from Georgia Tech alone, plus more from other schools, working for 48 hours to build interfaces with Moog Werkstatt-Ø1 analog synths, competing for $5,000 in cash prizes as well as Werkstatts for the top three teams.

We’re synth-fiends here on Hackaday: we cover everything from analog synths to voltage controlled filters.

Via Freeside Atlanta, photo by [Nathan Burnham].

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World’s Thinnest Morse Code Touch Paddle

Morse code enthusiasts can be picky about their paddles. After all, they are the interface between the man and the machine, and experienced telegraphers can recognize each other by their “hands”. So even though [Edgar] started out on a cheap, clicky paddle, it wouldn’t be long before he made a better one of his own. And in the process, he also made what we think is probably the thinnest paddle out there, being a single sheet of FR4 PCB material and a button cell battery. This would be perfect for a pocketable QRP (low-power) rig. Check it out in action in the video below.

There’s not much to a Morse code paddle. It could, of course, be as simple as two switches — one for “dit” and one for “dah”. You could make one out of a paperclip. [Edgar]’s version replaces the switches with capacitive sensing, done by the ATtiny4 on board. Because this was an entry in the 1kB challenge, he prioritized code size over features, and got it down to a ridiculous 126 bytes! Even so, it has deluxe features like autorepeat. We’d have to dig into the code to see if it’s iambic.
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Touch Piano Hits All the Right Notes

We love a good musical build, and this one is no exception. For their ECE4760 final project, [Wendian Jiang], [Hanchen Jin], and [Lin Wang] of Cornell built the nicest-looking touch piano we’ve seen in a while. It has five 4051 multiplexers that take input from 37 capacitive touch keys fashioned from aluminium foil and copper tape. Thanks to good debounce code, the sounds are clean even though the keyboard is capable of four-note polyphony.

A PIC32 and a Charge Time Measurement Unit (CTMU) module generate a small, steady current that charges up the keys. The PIC scans the pins continuously waiting for touch input. When human capacitance is detected, the value is compared with the base capacitance using the ADC and the sound is generated with the Karplus-Strong algorithm.

The group’s original plans for the project included a TFT screen to show the notes on a staff as they are played. While that would have been awesome, there was just too much going on already to be able to accurately capture the notes as well as their duration. Check it out after the break.

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Play Music with your Painting Using Teensy

[sab-art], a collaboration between [Sophia Brueckner] and [Eric Rosenbaum], has created a touch-sensitive musical painting. Initially, basic acrylic paint is used for the majority of the canvas. Once that is dry, conductive paint is used to make the shapes that will be used for the capacitive touch sensing. As an added step to increase the robustness, nails are hammered through each painted shape and connected with wiring in the back of the painting. These wires are then connected to the inputs of a Teensy++ 2.0, using Arduino code based on MaKey MaKey to output MIDI. The MIDI is then sent to a Mac Mini which then synthesizes the sound using Ableton Live.  Any MIDI-processing software would work, though. For this particular painting, external speakers are used, but incorporating speakers into your own composition is certainly possible.

A nice aspect of this project is that it can be as simple or as complex as you choose. Multiple conductive shapes can be connected through the back to the same Teensy input so that they play the same sound. While [sab-art] went with a more abstract look, this can be used with any style. Imagine taking a painting of Dogs Playing Poker and having each dog bark in its respective breed’s manner when you touch it, or having spaceships make “pew pew” noises. For a truly meta moment, an interactive MIDI painting of a MIDI keyboard would be sublime. [sab-art] is refining the process with each new painting, so even more imaginative musical works of art are on the horizon. We can’t wait to see and hear them!

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