Project Specification
Project Overview
Compact control board for a JC02-1 laser rangefinder, not a complete enclosure or laser module.
Intended Use
Mounted battery-powered rangefinder controller. First deliverable is an electrically captured prototype circuit and review; PCB layout requires a later checkpoint.
What the Device Should Do
Measure range using the external module, present readings on a rear-facing OLED, sense three-axis acceleration, communicate over Bluetooth, charge and monitor its single-cell LiPo, and accept USB firmware programming.
Main Features
- USB-C female: charging and USB firmware programming.
- Five-wire rangefinder interface: GND, regulated supply, module TX, module RX, active-high enable. User removed the original unused sixth wire.
- Bluetooth Low Energy is the working interpretation of Bluetooth; Classic Bluetooth is not included.
- Three-axis accelerometer, four momentary buttons, three-position Off/On/Settings slide switch.
- Generic 1.54-inch 128×64 monochrome SPI OLED with 3.3 V-compatible logic
- LiPo charger with power path and fuel gauge; charging remains available while Off only when USB source entitlement can be established safely.
- Limit power usage to extend battery life.
Mechanical System Architecture
Top controls -> compact main PCB -> cable-connected external OLED, rangefinder and protected battery.
OLED perpendicular to PCB, facing rear, extending below PCB. Three buttons in one row on the right side; fourth button left of row; slide switch forward of fourth button. All controls face upward. No enclosure CAD in this phase.
Electrical System Architecture
USB-C -> protection/source policy -> charger/power path -> switched 3.3 V logic supply and separately switched nominal 3.5 V rangefinder supply.
Battery -> protected pack connection -> charger/power path and always-available gauge.
Native-USB BLE MCU -> UART/enable rangefinder, SPI OLED, I2C accelerometer/gauge, buttons and Settings sensing.
Exact active parts require library and datasheet verification.
Hardware Subsystems
- Power: 4.2 V single-cell charger with load sharing; regulator inputs must tolerate charger system output as well as battery voltage.
- Compute: native USB programming with accessible boot/reset recovery, BLE, adequate GPIO.
- Sensor: low-power digital three-axis accelerometer.
- Display: bare OLED glass driver circuit.
- Protection: USB ESD, safe CC terminations, battery polarity plan and power-off isolation across domains.
Interfaces and Connections
Rangefinder original harness colors transcribed from uploaded manual: white GND; light blue VCC; green unused (removed); yellow module TX; black module RX; red enable. These remain provisional until checked on physical harness; new connector order need not match original numbering and must be labeled. Manual-transcribed electrical facts (not yet normalized to validated datasheet citations): supply 3.3–3.8 V; UART 9600 default or 115200,8N1; enable active high. Peak current and guaranteed UART/enable thresholds are unresolved.
Battery specifications: LP102540,1100mAh,3.7V nominal,4.2V charge endpoint,3.0V discharge endpoint,1C max charge/discharge; integrated protection circuit.
Power and Runtime Expectations
Charge target300mA, limited further by available USB source current and system demand. No runtime guarantee until active/idle measurements. Off physically disables system and rangefinder; gauge/charger remain upstream. Programming requires On or Settings. Settings runs UI without enabling laser by default.
Power Tree and Power Budget
Inputs: USB5V or protected LiPo. USB -> source-aware power path -> system feed ->3.3V logic buck-boost and3.5V LRF buck-boost. Separate LRF rail avoids placing the module exactly at its lower supply limit. Currents, conversion losses, inrush and runtime remain pending component selection; all combined battery loads must remain within the pack's reported1.1A limit. LRF output rating remains provisional until peak current is sourced/measured.
Manufacturing and Assembly Expectations
Smallest practical prototype rather than an unsupported fixed board-size promise. Prefer LCSC sourceable parts under applied profile, compact verified footprints and module-based RF. Four-layer PCB is a candidate for layout.
Firmware-Relevant Hardware Requirements
Native USB programming, boot/reset recovery, BLE services, UART protocol, OLED driver, four debounced inputs, Settings selection, battery state readout, low-battery orderly shutdown and USB current/suspend policy. Hardware must remain safe before firmware runs and during Off.
Physical Design Expectations
Preserve requested control arrangement and OLED orientation. Connector placement, mounting holes, battery/display geometry and final PCB dimensions deferred until sourced.
Important Design Decisions
300mA conservative charging target; use power path rather than charging a battery in parallel with an uncontrolled system load. Separate logic and LRF rails. Native-USB MCU module to avoid a separate USB-UART bridge. Do not use series resistance alone as proof of power-off isolation.
Assumptions
BLE is sufficient; bottom-side electronics permitted to reduce footprint; initial prototype is a board without enclosure. These are reversible defaults.
Change Notes
Five-wire connection omits NC. User selected Off/On/Settings, USB charging plus programming, compact requested mechanical arrangement and existing protected 1100mAh battery. User approved component selection and circuit capture before PCB layout.