Atlas

The hub and user interface for the Psychrometer sensor family: it concentrates periodic readings from miniature low-power nodes over a 2.4 GHz nRF24L01+ star network, displays them on an LCD, and may forward them to a local server.

Version: 0.1.0 | Status: concept

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Overview

Atlas is the mains-powered counterpart to the Psychrometer nodes. It listens on the nRF24L01+ star network, keeps the latest temperature / humidity / pressure reading from every node, and presents them on a 20x4 character LCD. Ambient light from a BH1750 drives automatic backlight and contrast so the panel is readable in the dark and in daylight. An optional uplink concentrates the data toward a local server.

graph LR
  S1[Node + BME280] -->|2.4 GHz| ATLAS
  S2[Node + BME280] -->|2.4 GHz| ATLAS
  SO[Outdoor node] -->|2.4 GHz| ATLAS
  ATLAS[Atlas hub<br/>STM32F103C8T6] --> LCD[(LCD 20x4)]
  ATLAS -. optional .-> SRV[(Local server)]
  BH[BH1750] --> ATLAS

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Hardware

Role	Part	Notes
Hub MCU	STM32F103C8T6	64 KB Flash, 20 KB RAM, bare registers
Radio	nRF24L01+	2.4 GHz, SPI1, PRX role, 3.3 V
Display	BC2004BGPLCH6	20x4 char, HD44780, 4-bit, 5 V
Light sensor	BH1750	I2C, ambient lux for auto bright/contrast
Contrast	PWM + RC on V0	timer-driven, auto from BH1750
Backlight	PWM via switch	timer-driven, auto from BH1750
Uplink	ENC28J60 (SPI)	dev board, to local server
Power	mains / 5 V	not power-constrained

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Scheduler

Task flow is driven by AcroSched 1.7 (static cooperative dispatcher), shipped as a prebuilt library (.a) plus public headers; sources stay private. Library parameters are compile-time and frozen at build:

Parameter	Value	Purpose
ACROSCHED_MAX_TASKS	12	~6 tasks + headroom
ACROSCHED_USE_WATCHDOG	1	IWDG refresh hook
ACROSCHED_USE_TIMERS	1 (MAX_TIMERS 4)	stale timeout, carousel
ACROSCHED_USE_IPC	1	mailbox/event flags (nRF IRQ -> task)
ACROSCHED_USE_IDLE_HOOK	1	__WFI() until next interrupt
introspection / stats / hooks	0	debug only

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Network

• Topology: star - up to 20 nodes report to Atlas (PRX).
• nRF24L01+ has 6 hardware pipes; node id in payload distinguishes nodes.
• Auto-ACK with retransmit; each reading carries id, T, H, P, battery/status.
• Stale flag if a node misses N transmit periods.

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Repository layout

Path	Purpose
inc/	Public headers
src/	Application sources (radio, render, sensors)
port/	STM32F103 register-level platform code
third_party/acrosched/	AcroSched lib (.a) + headers, frozen config
docs/	Doxygen config and diagrams
requirements.md	Requirements and task backlog
HISTORY.md	Milestone log
CHANGELOG.md	Versioned change log

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Toolchain

CMSIS-Toolbox, bare-register access (no HAL, no CubeMX).

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License

See LICENSE.