ESP32 Sauna Controller - THIS IS A WORK IN PROGRESS AND MAY NOT BE COMPLETE

A smart sauna controller built with ESPHome, featuring temperature monitoring, automated safety cutoffs, and Home Assistant integration.

Overview

This project creates a fully-functional sauna controller with:

• Real-time temperature monitoring (°C and °F)
• 16x2 LCD display with time and temperature
• Automated safety features (overheat protection, 6-hour auto-shutoff)
• Smart temperature control (auto-resume heating when safe)
• Home Assistant integration with notifications
• Web interface for remote control

Table of Contents

• Features
• Hardware Requirements
• Wiring Diagram
• Software Setup
• Safety Features
• Home Assistant Integration
• Troubleshooting
• License

Features

Core Functionality

• Temperature Monitoring: DS18B20 waterproof probe with 5-second updates
• LCD Display: 16x2 I2C display showing date, time, temperature (°C/°F), and heater status
• Relay Control: Control of sauna heater

Safety Features

• Overheat Protection: Automatic shutoff at 200°F (93.3°C)
• Auto-Resume: Resumes heating when temperature drops below 190°F (87.8°C) if master switch is still on
• 6-Hour Timeout: Automatic shutoff after 6 hours of continuous operation
• Temperature Alerts: Notification when sauna reaches 160°F (71°C)

Smart Features

• Home Assistant Integration: Full control and monitoring through HA dashboard
• Web Interface: Built-in web server for standalone control
• OTA Updates: Wireless firmware updates
• WiFi Fallback: Creates backup hotspot if main WiFi fails

Hardware Requirements

Required Components

Component	Specification	Qty	Estimated Cost	Source
ESP32 WROOM-32	DevKit V1, 30-pin	1	$8	Amazon, AliExpress
1602 LCD Display	16x2 with I2C backpack (PCF8574)	1	$6	Amazon, AliExpress
DS18B20 Temperature Probe	Waterproof, 3-wire cable	1	$8	Amazon, AliExpress
Relay Module	5V, 10A+ rated, optoisolated	1	$5	Amazon, AliExpress
4.7kΩ Resistor	1/4W (may be built into or included w/ probe)	1	$0.10	Local electronics store
USB Power Supply	5V, 1A+	1	$5	Amazon
Wires	22 AWG for low voltage	-	$5	Amazon
Wago Connectors	221 series or similar	10	$10	Amazon, Home Depot
Project Enclosure	100x65x45mm (approx)	1	$8	DIY, Linked

Total Cost: ~$55

Optional Components

• 3D printed enclosure (STL files in /hardware folder)

Tools Needed

• Soldering iron and solder
• Wire strippers
• Multimeter
• Screwdrivers
• Computer with USB port

Wiring Diagram

Pin Connections

Component	Wire/Pin	→	ESP32 Pin	Notes
DS18B20 Temp Probe
Red wire	VCC	→	3.3V	Power
Black wire	GND	→	GND	Ground
Yellow wire	DATA	→	GPIO4	OneWire data
(Optional)	4.7kΩ Resistor	→	Between DATA & 3.3V	Pull-up (may be built-in)
1602 LCD (I2C)
VCC	Power	→	5V	Check your LCD voltage
GND	Ground	→	GND	Common ground
SDA	Data	→	GPIO21	I2C data line
SCL	Clock	→	GPIO22	I2C clock line
Relay Module
VCC	Power	→	5V	Most relays need 5V
GND	Ground	→	GND	Common ground
IN	Signal	→	GPIO26	Relay trigger

Visual Wiring Diagram

                    ┌─────────────────┐
                    │   ESP32 WROOM   │
                    │                 │
   ┌────────────────┤ 3.3V            │
   │    ┌───────────┤ GND             │
   │    │  ┌────────┤ GPIO4           │──► DS18B20 Data (Yellow)
   │    │  │  ┌─────┤ GPIO21          │──► LCD SDA
   │    │  │  │  ┌──┤ GPIO22          │──► LCD SCL
   │    │  │  │  │┌─┤ GPIO26          │──► Relay IN
   │    │  │  │  ││ │ 5V              │──┐
   │    │  │  │  ││ └─────────────────┘  │
   │    │  │  │  ││                      │
   │    │  │  │  ││  ┌──────────────┐   │
   │    │  │  │  ││  │  1602 LCD    │   │
   │    │  │  │  │└──┤ SDA          │   │
   │    │  │  │  └───┤ SCL          │   │
   │    │  │  │      │ VCC ◄────────┼───┤
   │    │  │  │   ┌──┤ GND          │   │
   │    │  │  │   │  └──────────────┘   │
   │    │  │  │   │                     │
   │    │  │  │   │  ┌──────────────┐   │
   │    │  │  │   │  │ DS18B20      │   │
   │    │  │  └───┼──┤ Data (Yellow)│   │
   │    │  │      │  │ GND (Black)  │   │
   └────┼──┼──────┤  │ VCC (Red)    │   │
        │  │      │  └──────────────┘   │
        │  │      │                     │
        │  │      │  ┌──────────────┐   │
        │  │      │  │ Relay Module │   │
        │  │      └──┤ GND          │   │
        │  └─────────┤ IN (Signal)  │   │
        │            │ VCC ◄────────┼───┘
        │            └──────────────┘
        │
        └─── Common Ground Bus


     HIGH VOLTAGE SIDE (⚡ DANGER!)
     ┌──────────────────────┐
     │ Relay Output         │
     │ COM ◄─── Line (Hot)  │
     │ NO  ───► To Heater   │
     │ NC  (not used)       │
     └──────────────────────┘

Important Wiring Notes

⚠️ CRITICAL SAFETY WARNINGS:

• The relay output side carries MAINS VOLTAGE (120V/240V)
• Use proper electrical junction box
• Follow local electrical codes
• Use minimum 12 AWG wire for heater connections
• Consider hiring a licensed electrician for the high-voltage connections

✓ Best Practices:

• Use Wago 221 lever connectors for reliable connections
• Keep all low-voltage wiring away from high-voltage
• Use colored wire for easy identification
• Label all connections
• Test continuity before applying power

Software Setup

Two Installation Methods

You can set up this controller in two ways:

Method 1: Standalone (No ESPHome Installation Required) ⭐ EASIEST

Perfect if you just want a working sauna controller without installing anything on your computer!

What you get:

• Web interface at http://saunacontroller.local or device IP address
• Toggle sauna on/off from your phone/computer browser
• View temperature in real-time
• Works on your WiFi or its own hotspot

Steps:

1. Download the pre-compiled .bin firmware from the Releases page
2. Flash to ESP32 using ESPHome Web Flasher
3. Connect ESP32 via USB to computer
4. Open https://web.esphome.io/ in Chrome/Edge browser
5. Click "Connect" and select your ESP32
6. Click "Install" and choose the downloaded .bin file
7. After flashing, connect to "Sauna Fallback" WiFi (password: fallback123)
8. Configure your WiFi through the captive portal
9. Done! Access via http://saunacontroller.local or the IP shown on LCD

No computer software required after initial flash!

Method 2: DIY/Developer Method (With ESPHome)

If you want to customize the configuration or don't want to use pre-compiled firmware:

Prerequisites:

1. Install ESPHome

   pip install esphome

2. Create secrets.yaml file (optional but recommended)

   wifi_ssid: "YourWiFiSSID"
   wifi_password: "YourWiFiPassword"

ESPHome Configuration

Save this as saunacontroller.yaml:

# See full configuration in repository
esphome:
  name: saunacontroller
  friendly_name: SaunaController

esp32:
  board: esp32dev
  framework:
    type: arduino

# ... (full config in repo)

Standalone Usage (No Home Assistant)

Once flashed, your sauna controller works completely independently!

Accessing the Web Interface

On Your WiFi:

1. Open browser on phone/computer
2. Go to http://saunacontroller.local
3. Or use the IP address shown on the LCD display

Using Fallback Hotspot (if WiFi fails):

1. Connect to WiFi network "Sauna Fallback"
2. Password: fallback123
3. Go to http://192.168.4.1

Web Interface Features

The built-in web interface shows:

• 🌡️ Current temperature (live updates)
• 🔄 Sauna on/off toggle (click to control)
• 📊 Sensor status (temp probe, relay state)
• 📶 WiFi signal strength
• 🔄 Uptime counter

Example:

Sauna Controller
═══════════════════════

🌡️ Sauna Temperature: 165.2°F

🔥 Sauna: ○ OFF  [Toggle]

🔥 Sauna Heater: OFF

📶 WiFi Signal: -45 dBm

⏱️ Uptime: 2d 5h 32m

Changing WiFi Settings (Standalone)

If you need to connect to a different WiFi network:

1. Power on the ESP32
2. Wait 30 seconds for it to try connecting
3. If connection fails, it creates fallback hotspot
4. Connect to "Sauna Fallback" (password: fallback123)
5. Captive portal automatically opens
6. Enter your new WiFi credentials
7. Device will reboot and connect

No computer needed for WiFi changes!

OTA Updates (Standalone)

Even in standalone mode, you can update firmware wirelessly:

1. Compile new firmware (on any computer with ESPHome)
2. Go to http://saunacontroller.local
3. Click "OTA Update"
4. Upload the new .bin file
5. Wait for update to complete

Or use the web flasher:

1. Download new firmware from releases

2. Go to https://web.esphome.io/

3. Connect via USB

4. Flash new version

5. Connect ESP32 to computer via USB

6. Compile and flash:

   esphome run saunacontroller.yaml

7. Select COM port when prompted

8. Wait for compilation and upload (~2-5 minutes)

9. Check logs for sensor detection:

   [Dallas] Found sensors:
   [Dallas]   0x28FF1234567890AB
   

10. Update configuration with your sensor's address (replace 0x1234567890abcdef)

11. Flash again with correct sensor address

Subsequent Updates (Wireless OTA)

After initial USB flash, use wireless updates:

esphome run saunacontroller.yaml --device saunacontroller.local

Or update through Home Assistant's ESPHome dashboard.

Finding Your DS18B20 Address

The sensor address appears in logs during first boot:

[Dallas] Found sensors:
[Dallas]   0x28FF1234567890AB  <-- This is your address

Update this line in your config:

sensor:
  - platform: dallas_temp
    address: 0x28FF1234567890AB  # <-- Your sensor address here

Finding Your LCD I2C Address

Common addresses are 0x27 or 0x3F. The config will scan and show in logs:

[i2c] Found device at address 0x27

If your LCD doesn't work, try changing:

display:
  - platform: lcd_pcf8574
    address: 0x3F  # Try 0x3F if 0x27 doesn't work

Safety Features

Overheat Protection

Trigger: Temperature exceeds 200°F (93.3°C) Action:

• Relay immediately turns OFF
• Master switch stays ON (user intent preserved)
• Event sent to Home Assistant: esphome.sauna_overheat
• Display shows heater OFF

Auto-Resume: When temperature drops below 190°F (87.8°C) and master switch is still ON, heating automatically resumes.

6-Hour Auto-Shutoff

Trigger: 6 hours of continuous operation Action:

• Master switch turns OFF
• Relay turns OFF
• Event sent to Home Assistant: esphome.sauna_timeout
• Prevents accidental overnight operation

Temperature Ready Alert

Trigger: Temperature reaches 160°F (71°C) Action:

• Event sent to Home Assistant: esphome.sauna_ready
• One-time notification per heating session
• Resets when you turn sauna off

Home Assistant Integration (Optional)

Note: Home Assistant is completely optional! The sauna controller works perfectly standalone via its web interface.

However, if you use Home Assistant, you get these extra features:

• 📱 Mobile app notifications (sauna ready, overheat alerts)
• 🤖 Automations (schedule preheating, auto-shutoff rules)
• 📊 History graphs (temperature trends over time)
• 🗣️ Voice control ("Hey Google, turn on the sauna")
• 📲 Remote access (control from anywhere)

Automatic Discovery

The sauna controller will automatically appear in Home Assistant once ESPHome integration is set up.

Entities Created

• switch.sauna - Master control (what you toggle)
• binary_sensor.sauna_heater - Actual relay state (for diagnostics)
• sensor.sauna_temperature - Temperature in °C
• sensor.sauna_wifi_signal - WiFi strength
• text_sensor.sauna_ip_address - Device IP
• text_sensor.sauna_wifi_ssid - Connected network

Setting Up Notifications

Add to your configuration.yaml:

automation:
  - alias: "Sauna Ready Notification"
    trigger:
      - platform: event
        event_type: esphome.sauna_ready
    action:
      - service: notify.mobile_app_your_phone
        data:
          title: "🔥 Sauna Ready!"
          message: "{{ trigger.event.data.message }}"
          data:
            tag: "sauna_ready"
            group: "sauna"

  - alias: "Sauna Overheat Alert"
    trigger:
      - platform: event
        event_type: esphome.sauna_overheat
    action:
      - service: notify.mobile_app_your_phone
        data:
          title: "⚠️ SAUNA OVERHEAT"
          message: "{{ trigger.event.data.message }}"
          data:
            priority: high
            tag: "sauna_alert"
            group: "sauna"

  - alias: "Sauna Auto-Shutoff"
    trigger:
      - platform: event
        event_type: esphome.sauna_timeout
    action:
      - service: notify.mobile_app_your_phone
        data:
          title: "🛑 Sauna Auto-Off"
          message: "{{ trigger.event.data.message }}"
          data:
            tag: "sauna_timeout"
            group: "sauna"

Replace notify.mobile_app_your_phone with your actual notification service.

Dashboard Card Example

type: entities
title: Sauna Controller
entities:
  - entity: switch.sauna
    name: Sauna
  - entity: binary_sensor.sauna_heater
    name: Heater Status
  - entity: sensor.sauna_temperature
    name: Temperature
  - type: divider
  - entity: sensor.sauna_wifi_signal
    name: WiFi Signal

Or use a thermostat card:

type: thermostat
entity: switch.sauna
name: Sauna

Troubleshooting

Temperature Shows NaN or No Reading

Symptoms: LCD shows --°F or logs show [Dallas] Found no devices!

Solutions:

1. Check wiring:

   • Yellow wire → GPIO4
   • Red wire → 3.3V
   • Black wire → GND

2. Verify connections:

   • If using Wago connectors, ensure wires are fully inserted
   • Check for loose connections

3. Add pull-up resistor:

   • 4.7kΩ between yellow wire (data) and 3.3V
   • Some probes have this built-in, some don't

4. Try different GPIO pin:

   • Change pin: GPIO4 to pin: GPIO15 or pin: GPIO13
   • Move yellow wire accordingly

5. Enable internal pull-up:

   one_wire:
     - platform: gpio
       pin: 
         number: GPIO4
         mode:
           input: true
           pullup: true

6. Check sensor address:

   • Look in logs for actual address
   • Update in configuration

LCD Not Working

Blank Screen:

• Check power: VCC to 5V (or 3.3V depending on LCD)
• Verify I2C address: try 0x27 or 0x3F
• Check contrast potentiometer on I2C backpack

Garbled Text:

• Wrong I2C address
• Loose SDA/SCL connections
• Try lower I2C frequency: frequency: 100kHz

No Backlight:

• Some I2C backpacks have jumper to enable/disable backlight
• Check jumper position

Relay Not Clicking

No Response:

1. Check GPIO26 connection
2. Verify 5V power to relay VCC
3. Measure voltage on IN pin when toggling (should be 3.3V HIGH / 0V LOW)
4. Try inverting logic: add inverted: true to switch config

Clicks But Doesn't Control Heater:

• Check high-voltage wiring on output side
• Verify relay is rated for your heater's current
• Test with multimeter in continuity mode

WiFi Connection Issues

Won't Connect:

1. Check SSID and password
2. Move closer to router
3. Check 2.4GHz network (ESP32 doesn't support 5GHz)
4. Look for fallback hotspot "Sauna Fallback"

Frequent Disconnects:

• Weak signal (check WiFi strength sensor)
• Router compatibility
• Add to router config: wifi_band: 2.4ghz_only

ESP32 Won't Boot

Symptoms: LED not flashing, no serial output

Solutions:

1. Check power supply (needs 500mA minimum)
2. Try different USB cable
3. Press BOOT button while connecting to enter flash mode
4. Check for short circuits

Display Shows Wrong Time

Issue: Time is incorrect or not showing

Solutions:

1. Verify Home Assistant connection
2. Check timezone setting in config
3. Ensure Home Assistant time is correct
4. Internet connection required for NTP sync

Maintenance

Regular Checks

• Weekly: Verify temperature readings are accurate
• Monthly: Clean LCD display
• Quarterly: Inspect wiring connections
• Annually: Test all safety features

Testing Safety Features

Overheat Protection Test:

1. Set up monitoring
2. Allow sauna to reach 195°F
3. Verify relay turns off at 200°F
4. Verify relay turns back on below 190°F

Auto-Shutoff Test:

1. Turn sauna on
2. Set timer for 6 hours
3. Verify automatic shutoff

⚠️ Never disable safety features in production use

Project Structure

sauna-controller/
├── README.md                    # This file
├── saunacontroller.yaml         # Main ESPHome configuration
├── secrets.yaml.example         # Template for WiFi credentials
├── docs/
│   ├── wiring-diagram.png       # Detailed wiring diagram
│   ├── assembly-guide.md        # Step-by-step assembly
│   └── troubleshooting.md       # Extended troubleshooting
├── hardware/
│   ├── enclosure-base.stl       # 3D printable base
│   ├── enclosure-lid.stl        # 3D printable lid
│   └── mounting-template.pdf    # Drilling template
└── home-assistant/
    ├── automations.yaml         # Example HA automations
    ├── dashboard.yaml           # Example dashboard card
    └── scripts.yaml             # Helper scripts

Future Enhancements

Potential improvements for v2.0:

• Add humidity sensor (DHT22/BME280)
• Implement PID temperature control
• Add physical buttons for manual control
• RGB status LED
• Door sensor integration
• Energy monitoring
• Scheduling preheating
• Voice control integration
• Mobile app with push notifications

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

License

This project is licensed under the MIT License - see the LICENSE file for details.

Acknowledgments

• Built with ESPHome
• Integrates with Home Assistant
• Thanks to the open-source community for libraries and support

Support

If you encounter issues:

1. Check the Troubleshooting section
2. Review ESPHome logs for errors
3. Open an issue on GitHub with:
   • Your configuration file (redact WiFi credentials)
   • Complete error logs
   • Photos of wiring if relevant

Safety Disclaimer

⚠️ IMPORTANT: This project involves:

• High voltage electrical work (120V/240V)
• Control of heating elements
• Potential fire hazards if improperly installed

You are responsible for:

• Following local electrical codes
• Proper installation and testing
• Regular maintenance and inspection
• Understanding your sauna's requirements

Recommendations:

• Have a licensed electrician review your installation
• Install proper circuit breakers and GFCI protection
• Never leave sauna unattended while heating
• Ensure proper ventilation
• Keep fire extinguisher nearby

The author assumes no liability for damages, injuries, or losses resulting from use of this project.

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Version: 1.0.0 Last Updated: January 2026 Author: Rob Waldhauser