ESP32 Solar IoT Automation Hub

An ESP32-based solar-powered IoT automation hub featuring environmental sensing, local Wi-Fi MQTT connectivity, an OLED status display, and a 4-channel relay control module designed for indoor home automation.

Executive Summary

This reference design defines the system architecture, critical component candidates, risk register, and validation path for Solar IoT Automation Hub. It is a system-level design deliverable; verify critical claims with manufacturer evidence and prototype testing before production release.

Design Overview

Requirements Coverage

Requirement	Architecture coverage	Status
Monitor indoor temperature and humidity using DHT11	Pending validation	Needs verification
Track system voltage and current via dedicated sensor boards	Pending validation	Needs verification
Display real-time system status on a 0.96-inch I2C OLED display	Pending validation	Needs verification
Control external loads using a 4-channel relay module with status LEDs	Pending validation	Needs verification
Maintain timekeeping and accurate ADC readings via RTC/ADC module	Pending validation	Needs verification
Operate on a duty-cycled sleep mode powered by an 18650 Li-ion battery and dual solar chargers	Pending validation	Needs verification
Transmit telemetry locally via Wi-Fi to Home Assistant via MQTT	Pending validation	Needs verification

Item	Details
Product Type	Solar IoT Automation Hub
Key Functions	Monitor indoor temperature and humidity using DHT11, Track system voltage and current via dedicated sensor boards, Display real-time system status on a 0.96-inch I2C OLED display, Control external loads using a 4-channel relay module with status LEDs, Maintain timekeeping and accurate ADC readings via RTC/ADC module, Operate on a duty-cycled sleep mode powered by an 18650 Li-ion battery and dual solar chargers, Transmit telemetry locally via Wi-Fi to Home Assistant via MQTT
Power Source	Li-Ion Battery
Connectivity	WiFi
Size	Custom 3D-printed weatherproof enclosure
Environment	indoor
Difficulty	Intermediate
Est. Time	3-5 hours

System Architecture

Power Topology: USB-C 5V → MCU 3.3V LDO

Module List

Module ID	Type	Name	Function	Voltage
POWER	POWER	USB-C Power Jack	Power input	5V
MCU	MCU	ESP32-WROOM-32	Main controller	3.3V

Power Tree and Signal Interfaces

From	To	Type	Interface / rail	Voltage
POWER	MCU	power	Power	-

Design Schemes

Solar IoT Automation Hub ★

Key IC selection

main MCU and wireless telemetry controller

• Need: Provide dual-core processing, ultra-low power deep sleep modes, integrated Wi-Fi for MQTT, and sufficient GPIOs for I2C, DHT11, and 4-channel relay control.
• Class: Wi-Fi + BLE IoT Microcontroller Module
• Shortlist: Espressif ESP32-WROOM-32 series, Espressif ESP32-S3-WROOM series
• Pick: Select exact MPN based on required flash size (e.g., 4MB vs 8MB), operational temperature range (-40°C to 85°C), and stock availability in current distribution channels.

Dual solar charger and power path management

• Need: Manage simultaneous 18650 Li-ion battery charging from dual solar panels and USB-C input, provide reverse polarity protection, and deliver stable regulated 3.3V to the MCU during active and sleep states.
• Class: Solar Li-ion Battery Charger and Low-Quiescent Current LDO/Buck Regulator
• Shortlist: Linear Technology / Analog Devices MPPT solar charger ICs, Texas Instruments bq242xx / bq251xx solar power management family
• Pick: Select exact MPN based on solar panel open-circuit voltage rating, maximum charge current requirements, and ultra-low quiescent current (<10uA) to optimize duty-cycled sleep battery life.

Risk register

ID	Area	Severity	Detail	Mitigation
r1	power	high	Quiescent current of dual solar chargers, relay driver circuits, and auxiliary RTC/sensor modules may exceed the power budget during ESP32 deep sleep mode, draining the 18650 battery during extended low-sunlight periods.	Select power components with ultra-low quiescent current (<15uA total), implement high-side load switches to cut power to sensors, OLED, and relay coils during sleep cycles.
r2	thermal	med	Enclosure thermal accumulation from solar charging currents and continuous Wi-Fi transmission bursts can skew local DHT11 temperature and humidity readings.	Physically isolate the DHT11 sensor from heat-generating components (charging ICs, voltage regulators, and the ESP32 RF module) with adequate ventilation paths in the enclosure design.
r3	firmware	med	Wi-Fi reconnection and MQTT broker handshake overhead during frequent duty-cycled wakeups can consume excessive battery energy compared to active transmission time.	Optimize firmware to use static IP configuration, minimal MQTT keep-alive intervals, and fast-connect Wi-Fi profiles to reduce active radio-on time per duty cycle.

Bring-up and Validation Plan

1. Power-off inspection and rail resistance checks
2. Current-limited first power-up; verify every rail before enabling loads
3. Validate interfaces and timing one subsystem at a time
4. Run thermal, fault-injection, EMC pre-scan, and endurance tests for the target environment

Key Components

2/2 modules matched to real parts. See the BOM tab for the full component table.

USB-C Power Jack (TYPE-C-31-M-17)

The candidate MPN 'TYPE-C-31-M-17' matches the primary MPN exactly.

ESP32-WROOM-32 (ESP32-WROOM-32)

The candidate code exactly matches the primary MPN 'ESP32-WROOM-32' and is from the preferred manufacturer Espressif Sys

Build Summary

• Difficulty: Intermediate
• Estimated time: 3-5 hours
• Tools required: Soldering Station, Hot Air Rework Station, Digital Multimeter, Wire Strippers, Crimping Tool, Screwdriver Set

See the Build tab for the full step-by-step assembly guide.

Evidence and Limitations

• Confirm part parameters, certifications, and compatibility against current manufacturer documents.
• Treat industry compliance without test or certificate evidence as a compliance gap, not an approval.
• See Reference Images for visual artifacts and Build Guide for detailed assembly and bring-up steps.