Open Bed Climate — System Architecture

Clean-room design for an open-source, water-based bed climate system in the class of the Eight Sleep Pod. It is based on public facts only (product pages, FCC public exhibits, published community research, see ../research/prior-art.md). No vendor firmware, code or confidential documents are used. Protocols are our own.

Goals

Per-side water temperature control, 13–43 °C setpoint range, two independent zones (or one for Solo).
Presence, heart rate, breathing rate, movement from sensors in the cover; local-only by default.
Fully local operation: no cloud, no account, no subscription. Home Assistant / MQTT / local web UI.
Safety first: mains never leaves the hub; the cover carries only water and SELV wiring.
Buildable from standard parts. Tier 0 kits use off-the-shelf modules only. Tier 1 adds two reference PCBs (power board, cover sensor board). See hardware/README.md.

Non-goals (v1)

Compatibility with vendor covers/hubs (possible later via Pod 3–5 community protocol work, not in scope).
Designing our own adjustable base or speaker; we integrate existing products through Home Assistant instead.

Block diagram (Tier 1 reference; Tier 0 replaces the custom boards with off-the-shelf modules)

flowchart LR
  subgraph HUB[Hub enclosure]
    PSU[certified 24 V TEC supply\n+ 12 V aux supply] --> PWR[Power board\nTEC H-bridges x6\npump + fan drivers\nhot-swap + relays]
    MCU[Control MCU\nRaspberry Pi Pico 2 RP2350\nPID + supervisor] --> PWR
    SBC[Hub\nESP32-S3 + ESPHome or Raspberry Pi\nMQTT/HA, web UI,\nbiometrics, schedule] <-- OPL over UART --> MCU
    RES[Reservoir + level sensor] --> PUMPS[Pumps L/R]
    TEC[3–4 TEC per zone\non cold plates] --- HS[Heatsinks + fans]
    LEAK[Leak sensor\nhub floor] --> MCU
    TCO[Bimetal cutoffs\n50 °C / 80 °C] --> PWR
  end
  subgraph UMB[Umbilical]
    W[4 water lines]
    C[SELV 12 V + RS-485]
  end
  subgraph COVER[Cover]
    CH[Water channels L/R]
    SB[Cover sensor board\nRP2040, 9 piezo/side,\ncap. presence, temps]
  end
  PUMPS --> W --> CH --> W --> TEC
  SB <-- OPL over RS-485 --> SBC
  C --- SB

Split of responsibilities

Layer	Runs on	Owns	Must survive
Hardware safety	bimetal cutoffs on relay coils, hot-swap controllers, PSU OVP	absolute limits	MCU crash, firmware bugs
Real-time control	Control MCU, Pico 2 (Rust or C), same in both tiers	TEC current loop, PID, supervisor (`software/opod/src/opod/control.py` is the reference)	host crash: goes SAFE after 10 s without heartbeat
Hub software	ESP32-S3 with ESPHome (Tier 0 default) or a Linux SBC (heavier biometrics)	schedules, biometrics, MQTT/HA, web UI, OTA of MCU	can be rebooted at any time
Cover sensing	Cover MCU	sampling, sync, framing	—

Key principle: the hub can never cause an unsafe state. It can only request setpoints within 13–43 °C; the MCU clamps them, and hardware cutoffs clamp the MCU.

Documents

01-thermal-fluidics.md — TEC sizing, water loop, heat rejection (backed by opod.thermal)
02-electrical-safety.md — power, isolation, fault handling, standards
03-sensing-biometrics.md — cover sensors, BCG signal chain, algorithms
04-firmware-protocol.md — OPL wire protocol (backed by opod.protocol)
05-bed-software.md — hub services, schedule, HA integration
BOM.md — Tier 1 (Duo Reference) bill of materials; Tier 0 parts are in hardware/PARTS.md
OPEN-DECISIONS.md — what still needs a decision or a prototype measurement

Rendered from docs/design/00-architecture.md in the repository. View or edit the source.