Blog - Sketching with Hardware

Team 1 – Boom Box

Published on: | Author: Martin Gross | Categories: 2017a, Projects

The Boom Box, built by team 1 of the 2017A intake of SWH-students, tackles the proposed subject “MIDI Madness” in a very unique way. And in a very destructive one, nonetheless.

The basic idea behind this project is to not generate different tones by classical means like hitting objects to produce sound or by electronically producing them. Instead, it produces the sounds in a more destructive way: By employing small explosions.

When thinking about small explosions in electronics, capacitors come to mind as they tend to exhale their live quite easily and quickly when provided with a too high voltage. As popping capacitors this way is quite easy, we chose to go down that route. But it should be noticed, that emitting the “magic smoke” from electronic parts is not limited in any way to capacitors: Using resistors, LEDs and pretty much any other electronic part and a little too much voltage yields the same results.


Having decided on producing sounds by means of the “pop”ing of capacitors and other electric parts, we moved on to design a rig for this special type of instrument.

The easy way would have been to just use a handful of IO-expanders, paired to darlington transistor-arrays. This way, popping a component would have been as easy as switching a specific output-pin to cause the explosion. Using, for example, the Microchip MCP23017, we could have had 128 individual firing-positions: each IC offers 16 ports, whereas up to 8 devices can be daisy-chained onto on I²C-bus. This daisy-chain would have been connected to pins 20 (SDA) and 21 (SCL) respectively on the used Arduino Mega board (please note, that other Arduinos have different pins designated for the I²C-bus).

However, as this seminar was calling for creative use of available resources, it was decided to go down a more difficult route. In the end, our design consists of 5 identical rigs mounted onto a wooden board. The amount was chosen arbitrarily – given enough resources and space, even more rigs could have been made.


Every rig consists of only a few select parts: a stepper motor mounted on top of a wooden spacer, an acrylic disk mounted onto the steppers spindle and a electrical contact-system made out of foam, conductive tape and springs.

The stepper motor

Using provided parts, we chose the readily and cheaply available 28BVYJ-48 5V stepper motor, which is driven by a ULN2003 motor driver. Using the provided miniature PCB with the motor driver enables us to achieve very quickly results, as available Arduino-libraries may be used. Another advantage is that this stepper/driver-combination is only requiring 4 digital pins for control as well as 2 pins for power supply. Using a proper power supply, the latter two may be shared across all steppers. However, as the steppers do require an elevated amount of power, a separate power-supply instead of the Arduino-provided power should be used.

The acrylic disk

discThe acrylic disc is one of the central elements of our rig: It is where the tone-generating elements (the capacitors or – for testing purposes – piezos) are being attached to. By attaching this disc to the stepper motor, we can precisely control the position of the item, that is supposed to obtain the deadly amount of voltage. The pictured disc has been crafted to specifically fit the used stepper motor: not only the center cutout is matching the spindle of the stepper motor exactly, but also the amount of positions for the capacitors has been chosen with the technical data of the motor in mind: Knowing that each step of the motor turns exactly 11.25°, 32 positions had been chosen – that way every step will present a new capacitor to be electrocuted. The 11, 1mm holes per line provide a comfortable way to accommodate electric parts of different sizes and shapes – as long as they obey the 100mil spacing used in most electronic parts.

The contact system

contactfoamTrial and error drove us to use this specific setup to deliver the deadly amount of power to the electronic parts sitting on top of the acrylic disk. While two springs are mounted onto the base board underneath the rotating disc, a block of insulating, yet semi-flexible foam is attached to them. This allows for two degrees of flexibility: the foam is flexible enough to give way to the legs of the electric parts places onto the rotating disc while the springs act as a secondary safeguard if the foam happens to not be flexible enough.

Onto the foam, two lines of copper tape are applied – a narrower one towards the outside of the rotating disc, providing the grounding and a wider strip facing inwards for the destructive voltage. Making this secondary strip as wide as possible allows to accommodate different electric parts to be provided with the necessary voltage.

Wiring it all up

schematicLooking at the provided schematics, it becomes quite clear that not a lot of work has to go into the wiring of this device: In fact, the wiring is limited to connecting 4 wires per stepper to and the provided MIDI-interface to the Arduino, joining all ground connections and providing the necessary power supplies. In order to keep this devices as modular as possible, we opted in actually using three separate power supplies – but they could have been reduced down to one for sure. One power supply (+5V in the schematic) is used to power the Arduino, another 5V to 12V (Vss) is used to power the stepper motors. Lastly, Vcc/2 is used to deliver the deadly power to the capacitors riding the acrylic wheel. If one was to reduce those power supplies into a single one, caution should be employed: the explosion of the electric parts on the wheel may cause short circuiting which in turn may put the power supply out of service – either because of a blown out (poly-)fuse or bad craftsmanship.

Final thoughts

While this project certainly has been fun, it clearly has been a more of a demonstration how to quickly assemble a (more or less useless) device than producing a state of the art device with real-world usability. Just looking at the stability and precision of the device, it is clear that this device cannot be used for more than just demonstration purposes. While stepper motors offer some precision, the variances in the laser-cut discs is too high for 100% precise alignment with the electrical contacts underneath. Lastly it should be stressed, that this contraception should not be left unattended: While we only applied a minor amount of voltage to the contacts, theoretically even deadly 220V could be delivered. Either way it should be considered though that the spring-loaded mechanisms might touch and short-circuit, causing electrical damage or even fires. In short: this device is a nice demonstration of what not to build 😉


Arduino Sourcecode

linked categories 2017a, Projects


Write a comment


[…] Find a more detailed outline of the project here. […]

[…] And here: Project’s Overview and reflections […]