EZO RTD Temperature Monitor — Basic UI Dashboard

Overview

This project implements a real-time temperature monitoring system based on the Atlas Scientific EZO-RTD™ sensor module, interfaced via I²C to a Raspberry Pi. It extends a previous air quality monitoring platform (originally built around the HTU21D sensor) by replacing the temperature/humidity measurement stage with a high-precision RTD (Resistance Temperature Detector) circuit that provides temperature-only readings with significantly improved accuracy.

The system follows a layered architecture: a C daemon reads sensor data over I²C, writes it to a JSON file, and a lightweight HTML/CSS/JS dashboard served by Nginx polls that file every second to display live temperature readings in a browser.

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Hardware

Sensor: Atlas Scientific EZO-RTD™ (ISCCB-2 Module)

The EZO-RTD is a complete circuit board that conditions RTD signals and communicates digitally. It supports both UART and I²C protocols. In this project it operates in I²C mode.

Key specifications:

Parameter	Value
I²C Address	0x66
Supply Voltage	3.3 V – 5.0 V
Temperature Range	−126.000 °C to 1254.000 °C
Resolution	0.001 °C
Accuracy	±(0.1 °C + 0.0017 ×
Communication	I²C / UART
Response Time	≈ 1 s per reading

Wiring — ISCCB-2 → Raspberry Pi

ISCCB-2 Pin	Raspberry Pi Pin	Signal
VCC	Pin 1	3.3 V
GND	Pin 6	Ground
SDA	Pin 3 (GPIO2)	I²C Data
SCL	Pin 5 (GPIO3)	I²C Clock
OFF	—	Not connected

Note: The OFF pin is used to put the EZO circuit into low-power sleep mode. It is left unconnected in this implementation, meaning the circuit remains always active.

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Repository Structure

basic-ui-dashboard/
├── data/
│   ├── EZORTD.json          # Live temperature output (written by daemon)
│   ├── EZORTD.csv           # CSV log with timestamps (written by daemon)
│   └── HTU21D.json          # Legacy HTU21D data (retained from previous project)
├── images/
│   ├── thermometer-outline.svg
│   ├── water-outline.svg
│   ├── cloud-outline.svg
│   └── sunny-outline.svg
├── sensors/
│   ├── EZORTD/
│   │   ├── ezortd.h         # EZO RTD library header
│   │   ├── ezortd.c         # I²C communication implementation
│   │   ├── main.c           # One-shot executable (single reading → stdout)
│   │   ├── ezortd_daemon.c  # Continuous daemon (writes JSON + CSV log)
│   │   └── Makefile
│   └── HTU21D/              # Legacy sensor (retained for reference)
│       ├── htu21d.h
│       ├── htu21d.c
│       ├── main.c
│       └── Makefile
├── index.html               # Minimal dashboard (temperature only)
├── index-css.html           # Extended dashboard (temperature, humidity, CO₂, pressure)
└── README.md

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Prerequisites

Enable I²C on the Raspberry Pi

sudo raspi-config
# Navigate to: Interface Options → I2C → Enable
sudo reboot

Install Required Packages

sudo apt update
sudo apt install i2c-tools build-essential

Verify Sensor Detection

After wiring, confirm the EZO-RTD responds at address 0x66:

sudo i2cdetect -y 1

Expected output (address 0x66 should be visible):

     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:
...
60: -- -- -- -- -- -- 66 -- -- -- -- -- -- -- -- --

The EZO-RTD uses I²C bus 1 on the Raspberry Pi (pins 3 and 5). Confirm with ls /dev/i2c-*.

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Building the Sensor Programs

EZO RTD (primary sensor)

cd sensors/EZORTD
make

This produces two targets:

• EZORTD — single-shot binary. Reads one temperature sample and prints it as JSON to stdout:

./EZORTD
{ "temperature": 24.414 }

• ezortd_daemon (compiled separately) — continuous loop that writes data/EZORTD.json and appends to a CSV log every second:

gcc -o ezortd_daemon ezortd_daemon.c ezortd.c -I.
./ezortd_daemon &

Adjust the output file paths inside ezortd_daemon.c to match your local repository path before compiling.

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Serving the Dashboard

Install and Configure Nginx

sudo apt install nginx

Edit the default site configuration:

sudo nano /etc/nginx/sites-available/default

Replace the root directive:

root /home/pi/path/to/basic-ui-dashboard;

Restart Nginx:

sudo systemctl restart nginx

Open a browser and navigate to the device's hostname or IP address:

http://<raspberry-pi-ip>/

or, if mDNS is configured:

http://<hostname>.local/

The dashboard (index.html) polls data/EZORTD.json every 1 second and displays the current temperature value.

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Automating Data Updates

To keep the JSON file continuously updated, run the daemon as a background service or configure it to start on boot using systemd.

Minimal systemd unit (recommended)

Create /etc/systemd/system/ezortd.service:

[Unit]
Description=EZO RTD Temperature Daemon
After=network.target

[Service]
ExecStart=/home/pi/path/to/sensors/EZORTD/ezortd_daemon
Restart=always

[Install]
WantedBy=multi-user.target

Enable and start:

sudo systemctl enable ezortd
sudo systemctl start ezortd

Alternative: crontab (lower resolution, simpler)

sudo crontab -e

Add (updates every minute):

* * * * * /home/pi/path/to/sensors/EZORTD/EZORTD > /home/pi/path/to/data/EZORTD.json

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Dashboard Files

index.html — Temperature-only Display

Minimal single-sensor dashboard. Fetches data/EZORTD.json and refreshes every 1 second. Suitable for monitoring a single RTD probe.

index-css.html — Multi-sensor Dashboard

Extended dashboard supporting temperature, humidity, CO₂, and atmospheric pressure from multiple JSON sources. Sensor cards are currently wired to HTU21D.json; the other fetch calls are commented out pending integration of additional sensors.

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Migration Notes from HTU21D

The previous version of this project used the HTU21D sensor for combined temperature and humidity measurements. The EZO-RTD replaces only the temperature measurement stage. Key differences:

Aspect	HTU21D	EZO-RTD
I²C Address	0x40	0x66
I²C Bus	Bus 1	Bus 1
Measurements	Temperature + Humidity	Temperature only
Resolution	0.01 °C	0.001 °C
Communication library	libi2c (SMBus)	Raw I²C (linux/i2c-dev.h)
Read command	SMBus block read (0xE3)	ASCII "R" command, 1 s delay

The HTU21D source files are retained in sensors/HTU21D/ for reference.

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Troubleshooting

Sensor not detected at 0x66: Check that I²C mode is selected on the EZO-RTD. The default factory mode is UART. To switch to I²C, consult the Atlas Scientific EZO-RTD datasheet and follow the UART-to-I²C mode switching procedure.

ioctl: Operation not permitted: Run the executable with sudo or add the user to the i2c group:

sudo usermod -aG i2c $USER

JSON file not updating: Verify the daemon is running (ps aux | grep ezortd_daemon) and that the output path in ezortd_daemon.c is correct and writable.

Browser shows -- (no data): Confirm Nginx is serving files from the correct directory and that data/EZORTD.json exists and is valid JSON.

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Future Work

• Integrate remaining sensors: EZO-pH, EZO-DO, EZO-EC circuit
• Add historical data visualization using the CSV log
• Implement WebSocket-based push updates to replace polling
• Package the daemon as a proper systemd service with logging
• Add temperature alarm thresholds with visual/audible notification