CLASP
CLASP is a Bluetooth Low Energy (BLE) wearable project exploring proximity-based interaction logging through a bracelet form factor. Built around Nordic Semiconductor nRF52-series hardware, the system investigates low-power RF design, PCB iteration, enclosure design, and future synchronization with a mobile app to visualize real-world social connections over time.
Overview
CLASP is an exploration of Bluetooth Low Energy (BLE) in wearable devices. The goal is to create a bracelet that detects when it is in proximity to other CLASP bracelets and logs those interactions over time.
Rather than functioning as another social media platform, CLASP is intended to encourage real-world interaction while providing a way to visualize and reflect on the connections formed through everyday life.
While the long-term vision includes a bracelet form factor and a companion mobile application for syncing and displaying interaction data, the initial technical goal was to reliably detect proximity between multiple BLE devices using Nordic nRF52 microcontrollers.
Initial Prototypes
This project began as a learning exercise in PCB design through rough prototype circuits.
Early boards were designed in Autodesk Fusion 360 with an emphasis on low-power energy harvesting. Before refining the project toward social interaction logging, these prototypes focused on demonstrating basic PCB layout skills and powering LEDs using thermoelectric generator (TEG) plates.
Refined Prototype
After gaining confidence in PCB design, I developed a full BLE-enabled board. This iteration was built around the nRF52832-QFAA-R, a low-power RF microcontroller well-suited for wearable applications.
Additional components included:
- ADXL345 accelerometer for tap and motion detection
- M95P08 EEPROM for non-volatile storage
- Three onboard LEDs for status indication
- A 2.4 GHz radar component for RF experimentation
The PCB was fabricated through OSH Park, with components sourced from Digi-Key. At home, I laser-cut a solder-paste stencil from mylar and assembled the board using a homemade toaster-oven reflow setup.
This revision did not function as intended. Major issues included an improperly designed and untuned chip antenna, as well as excessive solder deposition caused by poor stencil tolerances.
Final Board
Incorporating lessons learned from earlier revisions, I designed Clasp V2.0. This board retained the nRF52832 microcontroller and ADXL345 accelerometer while introducing significant improvements:
- NPM1300 low-energy power management IC
- Support for LiPo batteries with USB-C charging
- PCB trace antenna replacing the chip antenna
- Smaller EEPROM package
- Improved layout for RF and power integrity
This revision functioned successfully and served as a stable development platform for the nRF52832, running Nordic example firmware without issue.
Enclosure
The current enclosure design is intended for a keychain-mounted form factor. The enclosure was designed to protect the electronics while keeping the device compact and wearable.
