Sensor HAT

Sensor HAT v3 "Universal"

Deutsch (ausführliche Anleitung): README.de.md

An open-hardware indoor-environment sensor board, designed in KiCad 10 (65 × 56 mm, 4 layers). It runs in one of two modes, never both at once:

1. HAT for Raspberry Pi 2, 3, 4 and 5, with a HAT+ ID EEPROM and Python.
2. Standalone with a plug-in Seeed Studio XIAO ESP32-S3, -C3 or -C6 (not included). It is powered over the XIAO's USB-C, runs ESPHome and shows up in Home Assistant.

Status: the design is complete. KiCad ERC and DRC report no errors, and the ESPHome configs validate. It has not been tested in hardware yet. Build prototypes before ordering in quantity.

What is on the board

All parts are in active production. The one exception is the ICS-43434 microphone: it is obsolete but still widely stocked.

Two LM66100 ideal diodes keep the two power sources apart, so no current flows from the Pi into the XIAO's USB port or the other way round.

Using it

XIAO mode (ESPHome / Home Assistant)

1. Copy the files for your XIAO from software/esphome/: sensor-hat-xiao-s3.yaml, -c3.yaml or -c6.yaml. You always need sensor-hat-common.yaml and a secrets.yaml as well. Start from secrets.yaml.example and fill in:

   • your Wi-Fi name and password
   • an API encryption key (openssl rand -base64 32), which also protects OTA updates
   • a password for the fallback hotspot (at least 8 characters)

   The placeholders in the template are rejected by esphome config on purpose. With more than one board, give each its own name: in the substitutions, for example sensor-hat-kitchen.

2. Flash the XIAO once over USB without the board attached. Then plug it into J7/J8 with the USB-C facing outwards. Later updates go over Wi-Fi. When you add the device in Home Assistant, it asks for the API encryption key.

3. Calibrate the readings:

   • set altitude_compensation to your altitude
   • after 15 minutes of running, enter the SHT40 offset against a reference thermometer

Notes:

• Power supply: at least 5 V / 1.5 A with the particulate sensor and radar connected, otherwise at least 1 A. A PC USB port is not enough.
• Battery: do not connect a battery to the XIAO.
• Antenna: use a U.FL antenna. This also applies to the C6: its chip antenna sits 11 mm above the ground plane. On the C6, also set restore_mode: ALWAYS_ON for the antenna_select switch in sensor-hat-xiao-c6.yaml (GPIO14 high selects the U.FL socket).
• Strapping-pin warnings: ESPHome warns about strapping pins on the C3 (GPIO2/8/9) and the S3 (GPIO3). These pins are pulled up or not sampled on this board, so the warnings are expected and harmless.

Raspberry Pi mode

1. Leave the XIAO socket empty.
2. Add the lines from software/config.txt.snippet to /boot/firmware/config.txt and reboot.
3. Run software/sensor_test.py. The pip packages it needs are listed at the top of the file.
4. To program the HAT+ ID EEPROM, see software/eeprom_settings.txt and the German README.

Solder jumpers: check them before you connect anything

• J3 radar: the pin order is V+, GND, module TX, module RX, OUT.
  • HLK-LD2420 and LD2410S fit directly (bridge JP1, 3.3 V).
  • LD2410C and LD2450 need JP3 (5 V) and a re-ordered cable.
  • In ESPHome, use sensor-hat-radar-ld2410.yaml for the LD2410/LD2410C and the ld2420 component for the LD2420. ESPHome has no UART support for the LD2410S, so only its OUT pin works (JP6 2-3).
• J4 particulate sensor: use a 6-pin JST GH cable wired pin 1 to pin 1 (VDD).
  • Check the cable with a multimeter first: crossed cables exist.
  • In XIAO mode use a SEN6x. A SEN5x needs at least 4.5 V, which is marginal on USB power.

Ordering

production/ holds JLCPCB files: Gerber zip, BOM and CPL in two variants. The "komplett" variant also has JLCPCB solder the through-hole headers and XIAO sockets. The 40-pin Pi socket J1 is always soldered by hand.

Recommended settings:

• 4 layers, 1.6 mm, ENIG
• Standard PCBA, top side only, peak 245 °C
• tooling holes added by JLCPCB. The board (65 × 56 mm) is smaller than the 70 × 70 mm Standard-PCBA minimum, so it needs edge rails: on the left and right edges and one on the top edge (about 75 × 70 mm in total), never on the bottom edge with the milled sensor island. Have JLCPCB confirm this.
• no board washing

The complete order remark is in the German README, section "Bei JLCPCB bestellen".

Estimated landed cost per assembled board for the SMD-only variant, incl. 19 % German VAT. You buy and solder the headers J1–J3, J7 and J8 yourself. python3 -I scripts/cost.py recalculates it with live part prices:

Small orders are expensive because of fixed setup fees, so a community group buy at cost is planned (German: docs/Sammelbestellung.md).

Repository layout

Building from source

pip install easyeda2kicad
python3 -I scripts/fetch_3d_models.py .   # LCSC 3D models, only needed for 3D view, renders, STEP
export FREEROUTING_JAR=/path/to/freerouting-2.5.0.jar
scripts/build.sh                          # schematic + ERC, board, autorouting, GND repair, DRC
python3 -I scripts/export.py .            # Gerber, BOM, CPL, PDFs, renders, STEP

Requirements:

• KiCad 10
• Java
• Freerouting 2.5

The scripts expect KiCad on macOS at ~/Applications/KiCad/KiCad.app. For other installations, change the paths at the top of build.sh, kicadlib.py, gen_pcb.py, route.py, cleanup.py and export.py. If your Java is not Homebrew's openjdk, run export JAVA=$(which java) before build.sh.

Licence

• Hardware (KiCad project, scripts/design.py and scripts/placement.py, production files, PDFs, renders): CERN-OHL-S-2.0
• Software and the other scripts: MIT
• Documentation: CC-BY-SA-4.0 or, at your choice, CERN-OHL-S-2.0

Source: https://github.com/Eniemooo/Sensor-HAT. Which licence covers which file is listed in LICENSE.md. Some symbols and footprints come from the LCSC/EasyEDA library, which has no licence of its own. These parts, and the trademarks, are listed in NOTICE.md.

Raspberry Pi is a trademark of Raspberry Pi Ltd. This project is not affiliated with Raspberry Pi Ltd or Seeed Studio. No warranty.