Execution Plan
Project
Low-power consumer temperature and humidity sensor node with:
- Digital temperature / relative humidity sensor
- Ultra-low-power MCU with integrated 2.4 GHz Wi-Fi 802.11 b/g/n and BLE 5.x
- USB-C 5 V default-source input
- Input protection covering reverse polarity, over-voltage, under-voltage lockout, and over-current protection
- Compatibility target: USB-C sources from 0.5 A to 3 A
High-Level Plan
1. Capture requirements and operating assumptions
- Define the product-level goals: sensing interval, battery/no-battery assumption, always-on vs duty-cycled operation, wireless update/reporting behavior, and expected consumer environment.
- Lock key electrical requirements for the USB-C input path: 5 V only, default USB-C sink behavior, acceptable input range, startup behavior, allowable peak/average current, and fault-handling expectations.
- Define sensing and wireless performance requirements: temperature/RH accuracy, response time, BLE/Wi-Fi use cases, provisioning method, antenna/enclosure constraints, and low-power targets.
- Capture review criteria early: power budget target, protection coverage, BOM availability, and manufacturability goals.
2. Build the system architecture
- Partition the design into major blocks: USB-C power entry, input protection, 3.3 V regulation/power management, MCU + RF, digital T/RH sensor, programming/debug, and optional status/user interface.
- Choose the USB-C sink strategy for 5 V default-source operation, including CC implementation and clear assumptions for interoperability with 0.5 A to 3 A sources.
- Define the protection chain architecture: ESD/TVS at connector, reverse-blocking strategy, over-voltage protection stage, UVLO behavior, and current limiting / over-current protection.
- Select the power tree and low-power strategy: regulator topology, sleep-state current goals, sensor power domain strategy, and any measurement or test hooks needed for current validation.
3. Implement the schematic in functional blocks
- Create the USB-C receptacle and input-power front end first, including CC resistors, protection devices, filtering, and the regulated system rail.
- Add the MCU subsystem with clocks, boot/configuration, decoupling, RF/antenna support, programming/debug access, and any required reset or enable circuitry.
- Add the digital temperature/humidity sensor, its interface to the MCU, required pull-ups/decoupling, and placement-aware design notes for later PCB work.
- Add system support circuitry such as indicators, test points, current-measurement options, and connectors only if they align with the low-power requirements.
4. Review, validate, and prepare for layout
- Run schematic/ERC reviews focused on power integrity, missing support parts, pull-ups, decoupling, and proper handling of unused pins.
- Review the protection strategy against the intended USB-C use cases: normal 5 V operation, source current range from 0.5 A to 3 A, reverse/incorrect input conditions, over-voltage events, UVLO behavior, and over-current response.
- Check the design against low-power intent: sleep-capable rails, leakage paths, regulator quiescent current, sensor standby behavior, and MCU wake/report cycle assumptions.
- Finish with a layout-readiness review covering RF antenna constraints, connector placement, power-entry current paths, grounding/decoupling strategy, and sourcing risk for critical parts.