Drumscale — Shipping scale to electronic drum
Hello world! I am a design student and recently, I converted a shipping scale into an electronic drum. With an art background, delving into the world of mechatronics was not an easy challenge, but an interesting moment. I am going to explain the process of this.
First, the mission that I got from the instructors was this: Take an existing object and replace its “guts” with a digital-enabled function. Design the new function with particular attention to the interface and aesthetic qualities that the object already possesses. We advise that you choose a single-minded and “simple” function. Demonstrate a deep understanding of the affordance of the object and what it communicates to people.
Find an object
I had to find an object that is perfect for my project. As someone who grew up in the ’90s, I wanted a product with a single-color display and not too sophisticated. Since I was not familiar with mechatronics, I thought it would be nice if it had just one function.
After searching through second-hand products, I found the one mentioned above. I decided to choose a product that primarily has one function and fewer buttons, because I preferred simplicity over complexity. Therefore, I selected a shipping scale, which seemed to have a clear utility.
Knowing the Function
After choosing the object, the first thing I started with was to understand its function. I researched how a digital scale works. Most scales use strain gauge technology. Even if I wanted to modify its function, I didn’t just want to maintain the appearance; I was interested in utilizing some of the existing technology. So, I looked into this technology further.
When an item is placed on a digital scale, the transducer beams bend, causing a change in electrical resistance. This change is measured by an Analog to Digital Converter, which sends the reading to the microcontroller. The microcontroller then calculates the precise weight using stored calibration data and displays the result. This process within the scale’s electrical components is almost instantaneous.
During the processing stage, scales with strain gauge load cells measure weight based on electrical resistance changes. As the load cell bends under weight, similar to a diving board, it stretches or compresses the strain gauges placed at specific points, altering the circuit’s resistance. This change in resistance affects the electrical current, which is measured in terms of input and output voltage, allowing stress to be quantified. The strain gauges, arranged in a zig-zag pattern for maximum deformation, are integral in measuring the strain experienced by materials under load. The scale amplifies these small voltage changes to calculate the weight.
In the out stage, reading electrical Signal to digital Reading phase, the scale calibrates by converting voltage readings from the load cell at zero load and maximum weight to digital values stored in memory, using accurate calibration weights to ensure precision. Known mass values, like 500g, help determine the conversion factor to translate voltage to weight. However, the process faces challenges from electrical noise, including electromagnetic waves from electronic devices, which can affect the accuracy of readings. Scales incorporate electromagnetic shielding, but strong interference may still cause fluctuations. To mitigate this, keep electronic devices away from scales and use anti-static measures in dry environments.
Generate Ideas
What ideas could have been generated using a strain gauge? While altering the primary function to preserve the original object, strain gauge, three ideas were conceived. For simplicity and effectiveness, the decision was made to create a MIDI player that functions as an electrical drum, allowing the instrument to be changed via buttons. During class, we had a critique session on our individual projects. It seems that my idea is solidifying towards musical instruments. I decided to draw the necessary diagrams to figure out what sensors are needed, and Kirk, who is currently taking a course related to instruments, agreed to help me with some parts. Unlike previous projects, this one feels more challenging because it involves disassembling an actual commercial product rather than creating something entirely new. I wonder if I should have chosen a simpler object, but I think taking on this challenge will be helpful.
Disassemble the scale
After that, I disassembled the shipping scale and to see the inner parts of it. It was more simple than I thought it would be. It had display, 4 buttons, strain gauge, 2 batteries, and a port for a power supplier. However, I was a bit afraid that I would miss some of the components and forget how to assemble all the components. I tried my best to document and I drew a diagram to make this better. I
I took photos of the lines carefully because I have to connect the existing lines after making the product. And I also melted the soldered parts, and separated the wires from the components.
Figuring out what to buy
Instead of immediately using the current strain gauge, I searched for tutorials on how to make a drum with Arduino and found that everyone uses piezo sensors.
Seeing this, I decided to first create one with a piezo sensor. There were small and large piezo sensors available; upon connecting them, they recognized stimulation and produced sound. However, the idea of using a different sensor felt like it wasn’t fully utilizing the original assignment, so I decided to proceed with using a strain gauge.
Strain gauges detect weight, but the weight detected was too minimal for the Arduino to recognize, necessitating an amplifier. I purchased an amplifier from Spark Fun and connected it to the strain gauge.
I wanted to preserve the original display, so I disassembled it to check if each part was lighting up with multimeter. Realizing that it would be challenging, I decided to purchase a new display of a similar size. The 7-segment display used in scales often has coding inside, and I wanted to try hacking it, but it seems I need to have at least intermediate electronics knowledge. Therefore, I plan to attempt this during the revision time in a month.
Arduino to Midi
I first connected my Arduino Uno to my Mac computer to find a way to use MIDI. It was common to use a MIDI converter, but the programs available for Mac were limited. I looked into Ardrumo, Serial MIDI bridge, Hairless MIDI<->Serial, virtual MIDI ports, MMJ, and other alternatives, but many were outdated. Therefore, I decided to purchase an Arduino Leonardo, which can be directly recognized as a MIDI device without the need for converters.
Display and buttons
Since I decided to use a new display, I contemplated what would be best and opted to try the seven-segment display I had already ordered. Although this display is much smaller than the original one, I decided to start with it to get the system running and ordered a 2.7-inch display that matches the size of the original display. Since the operation with the buttons worked well, I decided to continue using this display until the new one arrives.
Since the display and button experiments were successful, the next question was which buttons to use. I wanted to use the buttons that were already attached to the existing circuit. After connecting wires to the soldered parts on the back of the buttons and trying to run the code again, it didn’t work.
It seemed that being connected to the existing circuit prevented them from functioning, so I caused damage to the part of the circuit where the electricity was flowing, and then one of them worked successfully.
After numerous iterations, I realized I needed to add a 10MΩ resistor to the setup. The resistor I used was color-coded brown-black-orange-gold. Following this modification, when tested separately, the setup worked well.
Final output
Demo video.
Next step
- I will optimize the product and move everything inside of the scale
- I will make button-change instrument possible
- I want to convert the sound more dynamic and I will make it more interactive by ensuring that the sound changes depending on the weight.
- I want to change the outer black plastic package to metal that resembles with the touch area
