Introduction
By a couple of months I have started a project for creating a series of low-cost, open source, electronic musical instruments.
Dum-De-Dum is the first one of the series for which I have explored; an alternative way than using pressure sensitive pads to make a drum machine, reducing the costs of the components without penalising the performances of the final build.
Making a Cheap Drum Machine
According with the guidelines I drafted for designing a series of electronic musical instruments, the idea of the drum machine follows some basic assumptions.
Between vintage and poor (may be so poor?) materials the design should be limited to cardboard and super compressed cardboard, eventually MDF where special robustness is needed.
It is a must finding alternative technologies and methods than those usually adopted to reach the same result. If is not a fixation, just a way to discover new possibilities at dramatically lower production costs. In this case I have searched for something alternative than those touch sensitive pads for the user interaction, the key components of an electronic drum machine.
Despite the material and components, the final result is expected to be usable as well as an analogous commercial device.
Two commercial drum machine
Components and Methods
The design of the device and pads diameter (80. mm.) follows the most diffuses drum machines; the image below shows the quoted draft and pads distribution.
The base and percussion surface, of the pads has been obtained from a MDF sheet 3mm thick, while the remaining parts are built with cardboard.
To create the five sensitive pads I have opted for an unconventional solution: a set of five cheap weight sensors. The kit with the sensors, including their A/D amplifiers and converters based on HX711 costs about-5$. All together!
These sensors have a very good excursion, high sensitivity and can measure up to 5kg. All these parameters are in the range needed for the musical alternative use.
The drum A/D HX711 converters and the main connector to the Arduino board
Construction Details
The making of the construction of the cardboard drum machine is shown in the image gallery below. The components assembly has been done with hot glue, excluding the sensors, fixed to the pads and the MDF base with a couple of Allen screws.
| {gallery} Dum-De-Dum Making-Of |
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The 3mm MDF base. This will be the support of the weight sensors and pads |
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Cutting the robust base ... |
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Top view of the bottom side of the pad assembly (top surface) |
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This will be the surface cover of the structure. The entire forces are discarded on the pads and the sensors support, so this part does not need special robustness. |
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The double-sided pads. The top side is 3mm MDF, exposed to the user interaction forces while the bottom is glued cardboard, fixed on the weight sensors. |
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The pads ready to be assembled |
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The linear weight sensors screwed to the 3mm MDF base with the pads fixed on top. |
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Assembled view of the drum pads skeleton. The weight sensors can support up to 5Kg pressure |
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The pads assembled with the cardboard top cover |
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The 3mm MDF (bottom view) with an extra cardboard sheet glued on it. |
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Red pads rubber on top? |
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Naaa.... Better black, Be serious |
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Every pad sensor has its own HX711 A/D amplifier and converter. Around a cardboard border to complete the build |
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Bottom view of the structure |
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All te sensors signals collected by a small PCB and connected to the Arduino |
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The bottom of the Dum-De-Dum box. Initially the Arduino was external to the box but in its final assembly it is hosted inside the box. |
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Top view of the finished Dum-De-Dum (the cardboard drum |
Testing and Playing
The below video shows testing and playing (yes, it's me live playing a random rhythm 
) the Dum-De-Dum. Controlled by an Arduino board, the incoming sensors data are converted to a set of five predefined MIDI notes; the detected pressure intensity for every sensor is converted to a corresponding velocity value sent together with the associated MIDI note. This device can be used for live performances as well as to record rhythm sequences. In the video example the MIDI data are processed by Hydrogen, a great open source multi platform drum application.
The software is available instead on the GitHub repository DumDeDum.
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