Project Specification
Overview
Compact circular wireless sensor node, maximum 30 mm diameter, using ESP32-C3 for ESP-NOW communication.
Selected Architecture
- Single-board design
- 28 mm circular PCB
- Standard 4-layer stackup
- LiPo-powered operation with pogo-pin 5 V charging input
- UART + EN + BOOT pogo programming interface
Functional Blocks
- ESP32-C3-MINI-1 wireless MCU
- TMP117 contact temperature sensor located over the thermal sensing area
- LIS2DW12 accelerometer on shared I2C bus
- MCP73831 LiPo charger from external 5 V pogo input
- TPS63031 buck-boost regulator generating 3.3 V rail from LiPo
- JST-PH 2-pin LiPo battery connector
- Six pogo contacts for 5 V, GND, UART TX, UART RX, EN, BOOT
Key Electrical Decisions
- Buck-boost regulator used instead of a plain LDO so the 3.3 V rail remains valid across the LiPo discharge range.
- TMP117 thermal pad pin is intentionally left electrically floating to support thermal coupling without forcing an electrical ground connection.
- LIS2DW12 is wired in I2C mode with CS tied high and SA0 tied low.
- ESP32-C3 programming is exposed through pogo contacts rather than USB to save board area.
- Charger current is set near 300 mA using a 3.3 kOhm PROG resistor, appropriate for batteries above 300 mAh.
Mechanical Intent
- ESP32-C3 module placed near board perimeter with antenna facing outward.
- TMP117 placed near the center-bottom thermal contact region.
- Charger/regulator kept away from the temperature sensing region.
- Pogo contacts grouped along one accessible edge region for charging and programming fixture alignment.