Kelvin

A two-channel thermocouple logger you can read from the bench, your phone, or anywhere on your network.

What it is

An ESP32 with two K-type thermocouples and a small colour display. It shows both temperatures on its own screen, logs them to its flash, and serves the same data over Bluetooth, its own Wi-Fi access point, and your home network — so it is useful whether or not anything else is switched on.

• Two MAX31855 channels, −200 °C to +1350 °C, cold-junction compensated.
• Named faults instead of plausible wrong numbers — open circuit, short to ground, short to V_cc.
• On-board log ring, roughly a day at one sample a second.
• Android app for live readout, long-term archive and CSV export.
• Built-in web page, so any browser on the LAN works without installing anything.

Download

The app is signed with the project key and installs as an unknown source. Flash the firmware with esptool.py write_flash 0x10000 kelvin-node.bin, or push it over the air from the app once the node is on your network.

Getting started

1. Power the node. Its display shows the name of the Wi-Fi network it is broadcasting and the password.
2. Join that network from your phone, open the app, and connect to 192.168.4.1.
3. On the Node tab, give it your home Wi-Fi details. It stays reachable on its own network either way.
4. After that it answers to kelvin.local from anywhere on your LAN.