ESP32 Hardware Connection Guide

Solar Soil IoT

Complete step-by-step electronics wiring, pin assignments, and power regulation design

📦 1. Parts Inventory ⚡ 2. Power System Wiring 🌱 3. Main Sensor Node 📡 4. Gateway Node 🛡️ 5. Noise & Safety Passives 🔌 6. Quick Wiring Visualizer

This document details the hardware configurations for the two nodes comprising the **Solar Soil IoT System**: the battery-powered field **Main Sensor Node** (which collects metrics and transmits them via LoRa) and the wall-powered **Gateway Node** (which translates incoming LoRa packets into MQTT events over Wi-Fi).

📦 1. Parts Inventory (from Project BOM)

The following tables represent the components allocated from the project hardware manifest for both nodes.

Node A: Main Sensor Node Components

Component	Purpose	Priority	Reichelt Part No.
ESP32-C6 DevKit N8	Main RISC-V microcontroller with sleep support	Essential	`esp32-c6 n8`
SX1276 LoRa Module (868 MHz)	Wireless transceiver SPI breakout (RFM95W compatible)	Essential	-
LoRa Antenna 868MHz (SMA)	Provides high-efficiency RF transmission path	Essential	`ora_868_mhz_antenna_sma_plug`
Capacitive Soil Moisture v1.2	Analog soil moisture sensor (corrosion resistant)	Essential	`sensor_bodenfeuchte_-223620`
DHT22 Sensor Breakout	Reads ambient air temperature and humidity	Essential	`dht22`
INA219 Power Monitor	I2C High-side bus voltage and current sensing	Optional	`ina219`
Solar Panel 6V 2W	Charges batteries during sunlit hours	Essential	-
4x AA NiMH Batteries (GP ReCyko)	4.8V rechargeable battery pack	Essential	`recyko_nimh-akku_aa_mignon_2100_mah`
4x AA Battery Holder	Series battery carriage box	Essential	`holder AA`
LM2596 Buck Converter	Regulates fluctuating battery pack voltage to 5.0V	Essential	`2596-buvk-convtr`
Schottky Diode 1N5819	Blocks reverse flow from battery into solar panel	Essential	`in5819`
Passive Kit	4.7kΩ, 10kΩ resistors; 100nF, 10µF capacitors	Essential	-

Node B: Gateway Node Components

Component	Qty	Purpose	Priority	Reichelt Part No.
ESP32-C6 DevKit N8	1	Gateway logic supervisor and Wi-Fi station connection	Essential	`esp32-c6 n8`
LoRa Module 868MHz	1	Listens for sensor node telemetry frames (RFM95W/SPI)	Essential	-
LoRa Antenna 868MHz SMA	1	Ensures wide-area receive signal coverage	Essential	`ora_868_mhz_antenna_sma_plug`
OLED Display 0.96" SSD1306	1	Displays local network status, Wi-Fi IP, and metrics	Optional	`oled_display_0_96_128x64_pixels_`
USB 5V/2A Adapter	1	Steady 230V AC grid to 5V DC converter	Essential	-
USB-C Cable (1m)	1	Provides power and programming connection to ESP32	Essential	-

⚡ 2. Power System Wiring (Main Node)

The Main Node is solar-recharged and battery-buffered. Precision regulation is required to step down charging currents safely and protect the ESP32 input rails.

⚠️ Protection Diode Placement

You MUST install the 1N5819 Schottky Diode in series between the Solar Panel (+) and the Battery pack. Without this diode, the battery pack will discharge back into the solar panel cells overnight, causing cell degradation and rapid battery drainage.

[ SOLAR PANEL ]
  (+) ──────► [ 1N5819 DIODE (Anode) ] ── [ (Cathode) ] ──┐
  (-) ───────────────────────────────────────────────────┼──┐
                                                         │  │
                                                         ▼  ▼
                                                 [ BATTERY PACK (4.8V) ]
                                                         │  │
                                 ┌───────────────────────┘  │
                                 │   ┌──────────────────────┘
                                 ▼   ▼
                        [ LM2596 BUCK CONVERTER ]
                          IN(+) ─── IN(-)
                          OUT(+) ── OUT(-)
                            │         │
                            ▼         ▼
                      [ BREADBOARD POWER RAILS ]
                            (+) ────── (-)
                            (5V)     (GND)

Step-by-step Power Assembly Flow:

Connect the **Solar Panel Positive (+)** wire to the Anode (non-striped side) of the **1N5819 Schottky Diode**.
Connect the Cathode (striped side) of the diode to the **Battery Holder Positive (+)** lead.
Connect the **Solar Panel Negative (-)** wire directly to the **Battery Holder Negative (-)** lead.
Route the battery pack lines to the **LM2596 Buck Converter Input** (Battery + to `IN+`, Battery - to `IN-`).
Use a multimeter to measure the buck converter output. Use a small screwdriver to turn the copper potentiometer screw on the blue LM2596 board until the output voltage reads exactly 5.0V.
Connect the adjusted LM2596 outputs to the breadboard power rails (`OUT+` to Red rail, `OUT-` to Black rail).

💡 INA219 Monitor Integration (Optional)

To enable high-side current and voltage sensing, run the Battery Holder (+) line through the INA219 shunt pin headers:
Battery Holder (+) ──► INA219 VIN(+) ──► INA219 VIN(-) ──► LM2596 IN(+).

🌱 3. Main Sensor Node Connection Map

The following mapping connects the sensors and the SX1276 LoRa transceiver module to the **ESP32-C6** developer board on the breadboard.

ESP32-C6 Pin	Component Pin	Signal Name / Description
5V (or VIN)	LM2596 OUT(+)	Main 5.0V Power Input (Regulated)
GND	LM2596 OUT(-)	Common Ground Reference
3.3V	Sensors & LoRa VCC	Power distribution rail for low-power modules
GPIO 5	LoRa SCK	SPI Clock
GPIO 19	LoRa MISO	SPI Master In Slave Out
GPIO 27	LoRa MOSI	SPI Master Out Slave In
GPIO 18	LoRa SS / NSS	SPI Slave Select (Chip Select)
GPIO 14	LoRa RST	SPI Reset Line
GPIO 26	LoRa DIO0	LoRa Interrupt Request Pin (detects packet transmissions)
GPIO 4	DHT22 DATA	Single-bus Digital Temperature/Humidity Data Stream
GPIO 36	Soil moisture AOUT	ADC Analog Input (Soil Moisture Permittivity Voltages)
GPIO 21	INA219 SDA	I2C Serial Data
GPIO 22	INA219 SCL	I2C Serial Clock

📡 4. Gateway Node Connection Map

The Gateway Node relies on external USB supply. It utilizes a similar SPI interface for the LoRa module, and connects an optional 0.96" SSD1306 OLED screen over I2C to show diagnostic sync states.

ESP32-C6 Pin	Component Pin	Signal Name / Description
USB 5V	USB-C Port	Main 5.0V power input from wall adapter
3.3V	LoRa & OLED VCC	Powers the receiver module and I2C display panel
GND	LoRa & OLED GND	Common Ground Reference
GPIO 5	LoRa SCK	SPI Clock
GPIO 19	LoRa MISO	SPI Master In Slave Out
GPIO 27	LoRa MOSI	SPI Master Out Slave In
GPIO 18	LoRa SS / NSS	SPI Slave Select / CS
GPIO 14	LoRa RST	SPI Reset Line
GPIO 26	LoRa DIO0	LoRa Packet Rx Notification Line
GPIO 4	OLED SDA	I2C Data line for SSD1306 Display
GPIO 15	OLED SCL	I2C Clock line for SSD1306 Display
GPIO 16	OLED RST	OLED Screen Hardware Reset Pin

🛡️ 5. Noise and Safety Passives Placement

To prevent sensor reading jitter and ensure RF stability during LoRa transmission bursts, the passive components in the hardware kit must be connected as follows:

Power Rail Smoothing (10µF Capacitor):
Connect the 10µF Electrolytic Capacitor directly across the buck converter outputs (`OUT+` to `OUT-`) on the breadboard power rails. Pay attention to polarity (the gray stripe indicates the negative leg).
High-Frequency Decoupling (100nF Capacitor):
Connect the 100nF Ceramic Capacitor as close as possible to the LoRa module's VCC and GND pins. This suppresses high-frequency drops caused by RF transmitter pulses.
DHT22 Pull-Up Resistor (4.7kΩ):
Connect the 4.7kΩ resistor between the DHT22 VCC (3.3V) pin and the DHT22 DATA pin. This keeps the single-wire data line high by default to prevent communication dropouts.

🚫 Deep Sleep Voltage Restrictions

During deep sleep, the ESP32-C6 power draw is in micro-amps. Ensure that your LM2596 quiescent current does not drain the battery: if you find excessive draw, bypass the LM2596 LED power light by scraping its tiny PCB tracer to maximize battery longevity in the field.

🔌 6. Quick Breadboard Wiring Visualizer

Use these visual connection maps to complete your breadboard hookups quickly and reliably. Wires are color-coded to standard prototyping conventions.

🎨 Color Legend: ■ VCC (3.3V/5V) ■ GND (Ground) ■ SPI Bus ■ I2C Bus ■ Signals ■ Control

Main Sensor Node (Node A) Quick Diagram

+---------------------------------------------+ | BREADBOARD POWER RAILS | | [RED RAIL (+)] ◄─── LM2596 OUT(+) 5V | | [BLK RAIL (-)] ◄─── LM2596 OUT(-) GND | +---------------------------------------------+ ▲ ▲ │ │ (Passive Smoothing: 10µF Cap [+-] across Rails) │ │ +──┴───┴──────────────────────────────────────+ | ESP32-C6 DEV KIT | | | | (L) Pins (R) Pins | | [ RST ] [ 3.3V ] ────┼──► [To Sensors/LoRa VCC] | [ 3.3V ] [ GND ] ────┼──► [To GND Rail] | [GPIO 36] ◄── Soil (AOUT) [ 5VIN ] ◄───┼──► [From RED Rail +5V] | [GPIO 0] [GPIO 22] ────┼──► INA219 SCL | [GPIO 1] [GPIO 21] ────┼──► INA219 SDA | [GPIO 4] ◄── DHT22 DATA [GPIO 20] | | [GPIO 5] ───► LoRa SCK [GPIO 19] ◄───┼──► LoRa MISO | [GPIO 18] ───► LoRa CS/NSS [GPIO 27] ────┼──► LoRa MOSI | [GPIO 14] ───► LoRa RST [GPIO 26] ◄───┼──► LoRa DIO0 +---------------------------------------------+

LoRa SX1276 Pin	ESP32-C6 Pin	DHT22 Pin	ESP32-C6 Pin	Soil Moisture Pin	ESP32-C6 Pin
VCC (3.3V)	3.3V	1. VCC (3.3V)	3.3V	VCC (3.3V)	3.3V
GND	GND	2. DATA	GPIO 4	GND	GND
SCK	GPIO 5	3. NC	-	AOUT	GPIO 36
MISO	GPIO 19	4. GND	GND	INA219 Bus Connections
MOSI	GPIO 27	DHT22 Pull-Up: Connect a 4.7kΩ resistor between VCC (3.3V) and DATA (GPIO 4) pins.		SDA	GPIO 21
CS / NSS	GPIO 18			SCL	GPIO 22
RST	GPIO 14			VIN(+)	Battery Holder (+)
DIO0	GPIO 26	LoRa Decoupling: 100nF Cap across VCC and GND.		VIN(-)	LM2596 IN(+)

Gateway Node (Node B) Quick Diagram

+---------------------------------------------+ | GATEWAY BREADBOARD POWER | | [VCC RAIL (+)] ◄─── ESP32 3.3V OUT | | [GND RAIL (-)] ◄─── ESP32 GND OUT | +---------------------------------------------+ ▲ ▲ │ │ +──┴───┴──────────────────────────────────────+ | ESP32-C6 GATEWAY | | | | (L) Pins (R) Pins | | [ RST ] [ 3.3V ] ────┼──► [VCC RAIL (+)] | [ 3.3V ] [ GND ] ────┼──► [GND RAIL (-)] | [GPIO 36] [ 5VIN ] ◄───┼──► [5V USB Power Input] | [GPIO 4] ───► OLED SDA [GPIO 22] | | [GPIO 5] ───► LoRa SCK [GPIO 21] | | [GPIO 18] ───► LoRa CS/NSS [GPIO 19] ◄───┼──► LoRa MISO | [GPIO 14] ───► LoRa RST [GPIO 27] ────┼──► LoRa MOSI | [GPIO 15] ───► OLED SCL [GPIO 26] ◄───┼──► LoRa DIO0 | [GPIO 16] ───► OLED RST [GPIO 20] | +---------------------------------------------+

LoRa RX Pin	ESP32-C6 Pin	SSD1306 OLED Pin	ESP32-C6 Pin	Required Action
VCC	3.3V	VCC	3.3V	Continuous Power: Ensure the Gateway board remains powered via a USB-C cable hooked to the 5V/2A mains wall plug adapter.
GND	GND	GND	GND
SCK	GPIO 5	SDA	GPIO 4
MISO	GPIO 19	SCL	GPIO 15
MOSI	GPIO 27	RST	GPIO 16	OLED Setup: Uses software-driven I2C connection paths on pins 4 & 15.
CS / NSS	GPIO 18	-
RST	GPIO 14	-		LoRa Decoupling: Connect a 100nF decoupling capacitor across VCC and GND.
DIO0	GPIO 26	-