Divide To Conquer Capacitive Touch Problems

Back in the day, all of your music was on a shelf (or in milk crates) and the act of choosing what to listen to was a tangible one. [Michael Teeuw] appreciates the power of having music on demand, but misses that physical aspect when it comes time to “put something on”. His solution is a hardware controller that he calls MusicCubes.

Music cube makes selection using RFID, and touching to the right raises the volume level

This is a multi-part project, but the most recent rework is what catches our eye. The system uses cubes with RFID tags in them for each album. This part of the controller works like a charm, just set the cube in a recessed part of the controller — like Superman’s crystals in his fortress of solitude — and the system knows you’ve made your decision. But the touch controls for volume didn’t work as well. Occasionally they would read a false touch, which ends up muting the system after an hour or so. His investigations led to the discovery that the capacitive touch plates themselves needed to be smaller.

Before resorting to a hardware fix, [Michael] tried to filter out the false positives in software. This was only somewhat successful so his next attempt was to cut the large touch pads into four plates, and only react when two plates register a press at one time.

He’s using an MPR121 capacitive touch sensor which has inputs for up to 12-keys so it was no problem to make this change work with the existing hardware. Surprisingly, once he had four pads for each sensor the false-positives completely stopped. The system is now rock-solid without the need to filter for two of this sub-pads being activated at once. Has anyone else experienced problems with large plates as the touch sensors? Can this be filtered easily or is [Michael’s] solution the common way to proceed? Share your own capacitive touch sensor tips in the comments below!

Want to get a look at the entire project? Start with step one, which includes a table of contents for the other build logs.

Door Springs And Neopixels Demonstrate Quantum Computing Principles

They may be out of style now, and something of a choking hazard for toddlers, but there’s no denying that spring doorstops make a great sound when they’re “plucked” by a foot as you walk by. Sure, maybe not on a 2:00 AM bathroom break when the rest of the house is sleeping, but certainly when used as sensors in this interactive light show.

The idea behindĀ [Robin Baumgarten]’s “Quantum Garden” is clear from the first video below: engaging people through touch, sound, and light. Each of the 228 springs, surrounded by a Neopixel ring, is connected to one of the 12 inputs on an MPR121 capacitive touch sensor. The touch sensors and an accelerometer in the base detect which spring is sproinging and send that information to a pair of Teensies. A PC then runs the simulations that determine how the lights will react. The display is actually capable of some pretty complex responses, including full-on games. But the most interesting modes demonstrate principles of quantum computing, specifically stimulated Raman adiabatic passage (STIRAP), which describes transfers between quantum states. While the kids in the first video were a great stress test, the second video shows the display under less stimulation and gives a better idea of how it works.

We like this because it uses a simple mechanism of springs to demonstrate difficult quantum concepts in an engaging way. If you need more background on quantum computing, [Al Williams] has been covering the field for a while. Need the basics? Check out [Will Sweatman]’s primer.

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