Digital Wandering Pen

September 2024

The Wandering Pen is the result of a one-week rapid prototyping sprint at Brown and RISD’s Master of Arts in Design Engineering (MADE) program. I reimagined the conventional measuring tape to improve convenience, robustness, and versatility. Over multiple iteration rounds, I arrived at a more refined prototype: a digital pen that tracks the distance it has been rolled over a surface. This project was an excellent practice of rapid prototyping, user research, design refinement, and mechatronics. 


I aimed for breadth in my initial visualizations. These were narrowed down for prototyping based on novelty, personal challenge, and feasibility of prototyping. I also polled my classmates on which tools they would want to use, given that the target audience was design engineers aged 20-30.


Then, I made low-fidelity prototypes until I was blue in the face. 

Hand tattoo
Pop socket
Measuring tape pen v1
Measuring tape pen v2
Ring
Beaded Necklace
Foldable magnetic ruler
Water bottle
Sub sandwich!
Ribbon
Elastic band
High-resistivity wire
Encoder wheel
IR sensor
Multitool attachment

I composed a list of constraints and specifications to select the best prototype: 

Constraint    Specification
1. Quick to use    Time from pocket to measurement <15s 
2. Simple to use    <3 steps to measure
3. Accurate    Measures test piece to within ⅛” 
4. Visually appealing <75% of cohort polled agrees
5. Novel    No other cohort member is making a significantly similar product; not recognizable as a product on market by cohort
6. Technical    Displays >3 technical skills for a portfolio
7. Compact    Fits in a 6” pocket
The winner was the digital wandering pen, although the ring was a close second. The technical and novel constraints were my top priorities. With the pen selected, I created multiple design revisions. 


Electronics


This was half a day’s worth of work, and surprisingly the least troublesome part of the project. Due to the short timeline, I only used electronic components I had on hand: an encoder, an Arduino Nano, a 16x2-char LCD display, a 9V battery, and a power management breakout board. I tested encoder readings with two different Arduino libraries, then added in a display readout of the encoder’s distance traveled. While less sleek, I preferred the LCD over a 4-digit 7-segment display because it only uses 2 pins. 

First iteration
Freedom from the breadboard
Handheld rolling
Battery operation and digital display
Integration


Measurement Wheel


My biggest challenge in this project was the measurement wheel. My first prototypes slipped on most surfaces and decreased the accuracy of the measurement. I tried many different materials to increase the grip, and eventually settled on the spoked wheel. This worked the best on the chipboard block the class was given to standardize our measurements. 

Large wheel, rubber band
Small wheel, thick elastic
Textured rubber
Masking tape
Multiple small elastics
Sandpaper
Single small elastic
Poster mounting squares
Double-sided tape
Spoked wheel


Results


My initial vision was to use the device as a pen, although I also considered more horizontal computer-mouse-type orientations. I handed prototypes to my cohort members and saw where they gripped it, which led to dimension adjustments for various parts of the case. The most important feedback I received was that the device was top heavy due to the battery placement. The final device has a resolution of about 0.1”. When tested on multiple different surfaces, slipping brought the accuracy to 0.25” on average, which was more than sufficient to meet the challenge of measuring a 3’ chipboard test block.



Final Prototype and Future Iterations


Higher-fidelity prototypes would be made with soldered connections, which would eliminate the need for the power supply board and the excess wires. The device requires very little power, so I would use a much smaller battery and display, with the battery moved much lower to better distribute the weight. This would shrink the entire setup and allow the device to be much more like a pen. I would also like to examine a wider variety of materials for the scroll wheel than what I had on hand, with a focus on manufacturability. A production-level design should succeed on multiple surface materials and with a much smaller wheel for higher accuracy. 



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