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How it works

One core, many heads

All our devices share the same foundation, a board called Jádro (Czech for core). It carries an ESP32-C6 with WiFi 6, Bluetooth LE and an 802.15.4 radio for Thread and Zigbee, USB-C power, a Li-ion charger with battery voltage monitoring, two Qwiic ports for extra sensors, a status LED and a 6-pin connector for the head.

The head is what turns Jádro into a specific device. Hladina has a waterproof ultrasonic sensor, Úl four load cells with an HX711, Spot an LED ring and an OLED, Senzor a DS18B20 probe plus an SHT40. The firmware is always ESPHome, just with a different config.

The benefit is simple. Every device is set up the same way, uses the same power circuit and gets the same updates. If something fails, you replace only the faulty part. And if you want to measure something we do not offer, you can build your own head on the same Jádro. The head connector is an open specification, much like the expansion cards of Framework laptops. Heads and spare parts such as lids, gaskets, cable glands and cables will also be sold separately.

WiFi setup over Improv

Devices ship without your WiFi credentials. On first power up they wait for setup with the status LED on. You set up WiFi using the Improv standard in one of two ways:

  • From a browser. Connect the device to your computer over USB-C, open the setup page in Chrome or Edge and enter your network name and password.
  • From Home Assistant. If your Home Assistant has Bluetooth, it finds the waiting device on its own and offers WiFi setup right in the UI. You confirm the pairing by pressing the BOOT button on the device, so nobody can set up WiFi without having the device in hand.

There is no fallback WiFi network and no default password. No account, no registration, no app.

The status LED is a single plain LED: on while the device is not connected to WiFi, a short flash every 2 s in maintenance mode, off in normal operation.

Home Assistant

Once on the network, Home Assistant discovers the device through the ESPHome integration and offers to add it. After you confirm, all entities appear: measurements, battery voltage and settings such as thresholds, measurement interval or tank shape. You change settings directly in Home Assistant, no firmware edits needed.

Local web UI

Every device serves a simple web page on your local network with current values and device status. Handy for a quick check or if you do not use Home Assistant.

Optional MQTT

Running a different home automation system? Turn on MQTT and the device publishes its values to your broker, where any MQTT-capable system can pick them up.

Over-the-air updates

New firmware is installed over WiFi, no cables needed. We release updates in a public repository together with the source. If you build your own firmware in ESPHome Builder, you flash it the same way.

Battery operation and deep sleep

Hladina and Senzor tend to live far from an outlet, so they run on a common 18650 Li-ion cell. The cell is not included, you put it into the holder in the enclosure. To make it last, the devices use deep sleep: wake up at the set interval, connect to WiFi, measure, report and go back to sleep. They are awake for just a few seconds. By calculation (not measurement) a 3000 mAh cell at room temperature lasts about 10 months in Hladina at a 30 minute interval and about 6 months in Senzor at a 15 minute interval. Noticeably less in frost, a longer interval gives a proportionally longer life.

One consequence: while asleep, the device is unreachable. Home Assistant cannot send a setting change to a sleeping device. For setting changes and firmware updates there is maintenance mode, in which the device does not sleep. Turn it on with a Home Assistant helper (a toggle named "Plošná ryba údržba"), which the device reads on every wake.

The outdoor enclosures of Hladina, Senzor and Úl have no external USB-C port or buttons, so they stay waterproof. Sensor cables come routed through the glands and connected at the factory. Charge the cell by swapping in a charged one, or with the lid off over USB-C indoors, never below 0 °C. Úl measures continuously, has no battery and runs on 5 V from a common USB charger. Spot stays lit all the time, so it runs on USB-C.

No cloud

Devices talk only on your local network. We have no cloud and no app and send your data nowhere. The one exception is Spot in standalone mode, which downloads publicly available day-ahead spot prices from the internet when Home Assistant does not provide them.