Handheld Force-Sensing Probe Development

About the project

# Prototype Brief — Handheld Force-Sensing Probe ## Summary I need a working prototype of a small handheld instrument that measures the contact force applied through a thin rigid probing tip. When the tip is pressed against a surface, the device reads the applied force in real time and signals when a target force is reached. All sensing and electronics stay inside the handle; the tip itself is a slim passive pin. This is a proof-of-concept prototype, not a finished product. Priority is a fast, cheap, working demonstration. ## How it works (concept) - A thin, rigid probing tip is mounted on a shaft. - The shaft is free to slide a tiny amount (roughly 0.1–0.3 mm) inside the handle against a light preload spring. - Pressing the tip transfers axial force to a force sensor housed in the handle. - The electronics read the force, show it live, and trigger feedback (light + vibration) when a configurable target force is reached. - Force readings are also sent wirelessly (Bluetooth) to a phone/tablet or PC. The key design rule: **the part that touches the surface stays thin and passive; all sensing lives in the handle.** ## Functional requirements - Measure axial contact force through the tip, in roughly the 0.05–1.0 N range, with a configurable alert threshold set in firmware. - Live force value available over Bluetooth (BLE). - On-device feedback: an LED (e.g. green below threshold, red above) and a small vibration cue at the threshold. - Handle is sealed enough to survive wipe-down cleaning with disinfectant (no full waterproofing / autoclave needed). - Tip + shaft are removable stainless steel and contain no wiring. ## Form factor - Handle roughly pen-sized (about 12–16 mm diameter), balanced so it feels like a normal handheld instrument. - Tip stays slim (comparable to a fine probe pin). - Total length and weight kept close to a standard handheld probe. ## Suggested starting components (open to substitution) - Force sensor: small MEMS force sensor or micro compression/button load cell. - Signal conditioning: HX711 or ADS1220 ADC. - Controller with wireless: Seeed Xiao ESP32-C3 or nRF52840 (BLE). - Power: small rechargeable LiPo (100–150 mAh) with onboard charging. - Feedback: RGB LED + small coin vibration motor. ## Deliverables 1. Working prototype: probing tip + sliding shaft + force sensor + electronics inside a 3D-printed handle. 2. Firmware: reads force, converts to real units, drives the LED + vibration threshold, streams force over BLE. 3. Calibration: force reading validated against known weights, with the method documented. 4. Simple readout: a basic phone/PC display of the live force value (a minimal app or existing BLE viewer is fine). 5. Source files: firmware code, CAD files for the shaft/handle, wiring diagram, and a short build/calibration note. ## Skills needed (ideally one person) - Embedded electronics + firmware (load cell / ADC / microcontroller, BLE). - Mechanical design / CAD + 3D printing (the sliding-shaft mechanism and sealed handle). - A mechatronics or hardware-prototyping generalist is the ideal fit. ## To include in your proposal - Similar hardware prototypes you've built (with photos/links if possible). - Whether you can handle both the electronics and the mechanical/CAD side, or only one. - Rough cost and timeline to a working prototype. - Any parts you'd recommend changing and why. ## Terms - An NDA will be signed before detailed discussion. - All designs, code, and IP created for this project are assigned to me.

Skills required