Esp32c6-iot sensor node

ESP32-C6 Indoor Environmental Sensor Node

Production-oriented KiCad 8 reference design for a battery-powered indoor air quality node. The 50 x 50 mm, four-layer board combines:

• ESP32-C6-MINI-1-N4 with Wi-Fi 6, BLE 5.3, Zigbee and Thread;
• Bosch BME280 temperature, humidity and pressure sensing at I2C address 0x76;
• Sensirion SCD41 CO2 sensing in single-shot mode;
• a protected off-board 18650 cell through a keyed JST-PH connector;
• USB-C charging with TP4056, native USB Serial/JTAG and USB ESD protection;
• a 1.6 uA-Iq 3.3 V LDO and a hardware-gated SCD41 supply;
• reset, boot and six-pin UART recovery/programming access.

Release status

The native KiCad 8.0.9 project passes:

• schematic ERC: 0 errors;
• PCB DRC: 0 errors;
• unconnected-items check: 0 unconnected items;
• board size: 50.0 x 50.0 mm;
• nominal deep-sleep simulation: 11.8 uA, below the 15 uA requirement.

The remaining KiCad messages are non-electrical warnings for clipped or overlapping silkscreen inside stock library footprints and embedded library snapshot differences. They do not affect copper, solder mask, connectivity or fabrication.

Repository contents

• esp32c6_iot_sensor_node.kicad_sch - native KiCad 8 schematic.
• esp32c6_iot_sensor_node.kicad_pcb - routed four-layer PCB.
• esp32c6_iot_sensor_node.kicad_pro - project and JLC-compatible rules.
• sym-lib-table - explicit symbol-library mapping.
• design_spec.py - component, pin/net and placement source of truth.
• generate_schematic.py and generate_board.py - deterministic generators.
• finalize_routed_board.py - idempotent post-router connectivity finalizer.
• export_metadata.py - BOM and low-power analysis exporter.
• release/v1.0/manufacturing - fabrication, drill, BOM and CPL outputs.
• release/v1.0/analysis - machine-readable current and battery-life model.
• release/v1.0/docs - the visually verified rationale and schematic PDFs.
• release/v1.0/validation - machine-readable DRC/ERC reports and disclosure.
• release/v1.0/preview - STEP, GLB, board plots and digital preview video.

Architecture and design choices

Power path

USB-C VBUS feeds the TP4056 linear charger. R7 is 2.0 kOhm, programming about 500 mA so the thermally limited ESOP-8 charger and a normal USB source are not run at the 1 A headline limit. The battery rail feeds a ME6210A33M3G 3.3 V LDO with 10 uF input/output capacitors. The board accepts a protected 18650 cell only; protection is intentionally located in the cell/holder assembly so the 50 x 50 mm electronics remain serviceable.

The SCD41 can draw 205 mA peak at 3.3 V. C5 provides 100 uF local reservoir capacity, while Q1/Q2 create a default-off high-side switch controlled by SCD_GATE. Firmware must avoid simultaneous SCD41 conversion and maximum-power radio transmission because the selected low-Iq LDO is rated for 500 mA.

Sensors and I2C

The BME280 has local 100 nF decoupling, CSB tied high for I2C mode and SDO tied low through R13 for address 0x76. The SCD41 has 100 nF plus 100 uF local decoupling. R14 and R15 are explicit 4.7 kOhm pull-ups on SDA and SCL; no firmware-only pull-ups are assumed.

USB and recovery

The USB-C receptacle has independent 5.1 kOhm Rd resistors on CC1 and CC2. USBLC6-2SC6 protects D+ and D-, followed by 27 Ohm series resistors at the MCU side. C1/C2 are DNP tuning positions and must remain unpopulated unless a signal-integrity measurement calls for them. A six-pin header exposes 3V3, GND, UART TX/RX, EN and BOOT so a failed USB stack cannot brick the board.

RF layout

The ESP32-C6-MINI-1 antenna faces the board edge. A 43.2 x 5.7 mm all-copper and all-track rule area spans the antenna end of every copper layer. No parts, traces, vias or planes enter it. This follows Espressif's module-placement rule: place the PCB antenna at/outside an edge and minimize base-board material and copper beneath the antenna.

Deep-sleep and battery-life simulation

The release model uses published typical currents and a conservative leakage allowance:

The six-month mission profile assumes a 3000 mAh protected cell with 80% usable capacity, an SCD41 sample every ten minutes, two single-shot conversions after each cold start (discarding the first as Sensirion directs), a BME280 forced measurement every ten minutes, and one 120 mA/5 s radio upload per hour. The model yields 0.4275 mA average and about 234 days / 7.68 months. The exact calculation and inputs are in release/v1.0/analysis/power_budget.json.

This is a datasheet-based analytical simulation, not a fabricated-unit measurement. Production qualification must measure sleep current across cell voltage and temperature.

Firmware sequence

1. Hold SCD_GATE low during reset and while the ESP32 enters deep sleep.
2. Wake every ten minutes and trigger a BME280 forced measurement.
3. Drive SCD_GATE high, allow the SCD41 supply to settle, issue single-shot, discard the first post-power-up result, and take a second single-shot.
4. Store readings in RTC memory; transmit the accumulated batch once per hour.
5. Stop radio activity, drive SCD_GATE low, make USB pins high impedance when detached, and enter deep sleep.
6. Schedule forced recalibration or a periodic non-power-cycled calibration interval because hard power cycling prevents normal automatic self-calibration continuity.

Manufacturing

Recommended order:

• four layers, FR-4, 1.6 mm finished thickness;
• 1 oz outer copper and at least 0.5 oz inner copper;
• minimum track/space 0.20/0.20 mm;
• normal vias 0.60/0.30 mm;
• ENIG or lead-free HASL;
• controlled USB impedance should be recalculated for the fab's selected stack-up before volume production.

The two 0.60/0.30 mm vias inside the SCD41 exposed ground pad must be ordered as epoxy filled and copper capped (VIPPO) to prevent solder wicking. DNP C1 and C2 are excluded from the CPL. Test points are excluded from BOM and CPL.

Known limitations

• The board has no on-board cell protection; only use a protected 18650 cell/holder with correct JST polarity.
• TP4056 has no true power-path/load-sharing controller. Charging while the node is active can delay charge termination; firmware should sleep during charging where practical.
• The 500 mA LDO requires scheduling so the SCD41 peak and high-power radio TX do not coincide.
• SCD41 power cycling saves quiescent current but requires discarding the first reading and an explicit calibration strategy.
• Battery life is a simulation based on typical datasheet values and an 80% usable-capacity assumption. It must be verified on hardware.
• USB impedance has not been verified by TDR; recalculate against the exact production stack-up and use C1/C2 only after measurement.
• The design is not intrinsically safe, medical, automotive or outdoor-rated.

Primary references

• Espressif ESP32-C6-MINI-1 datasheet
• Bosch BME280 datasheet
• Sensirion SCD4x datasheet
• LCSC ME6210A33M3G listing
• LCSC 4.7 kOhm pull-up C23162