Fan: Two-point control

Scenario

An IOZER basic reads a 1-Wire temperature sensor and switches a fan through digital output 1. An enable datapoint activates the controller. The temperature setpoint and hysteresis have their own datapoints and can optionally be adjusted through Home Assistant.

The controller runs locally on IOZER. Home Assistant provides display and operation.

Goal

The two-point controller has two output states: fan on and fan off. Hysteresis separates the on and off thresholds so that small temperature fluctuations do not cause constant switching.

This example uses a temperature setpoint of 25 °C and hysteresis of 0.5 K:

Here, hysteresis is the offset from the temperature setpoint. With 0.5 K, the two switching thresholds are 1 K apart. Reaching exactly 24.5 °C or 25.5 °C does not trigger a state change.

Hardware used

• IOZER basic (IOZ-B-10) with a suitable power supply
• DS18B20 1-Wire temperature sensor
• Fan with a control interface suitable for the output
• Computer with access to the web interface
• Optional: Home Assistant with an MQTT broker

Requirements

• IOZER, the sensor, and the fan are installed according to the safety information and electrical connection instructions.
• I/O & Interfaces are active.
• The saved program is running for local control.
• For optional Home Assistant integration, IOZER and Home Assistant use the same MQTT broker.

Implementation

1. Configure the output and fan datapoint

Open I/O & Interfaces → Digital outputs and edit output 1.

Save and apply the output configuration. Then create its datapoint under Datapoints or using the plus icon in the output row:

The data source provides output feedback. The logic controls the data target using dp.set("luefter", true) or dp.set("luefter", false). Automatic forwarding of source values to the target is not required for these commands.

Labels and technical names match the German screenshots. Keep the technical names shown here when using the JavaScript examples. Further settings are described under Digital outputs.

2. Configure the temperature sensor and datapoint

Navigate to I/O & Interfaces → 1-Wire. Run sensor discovery if necessary and add the DS18B20 to the configuration.

Use the hardware address of your connected sensor. The address in the screenshot belongs to the example setup.

Create the temperature datapoint using the plus icon in the sensor row or under Datapoints:

Save and apply the configuration. The datapoint must show a plausible measurement with status OK and update regularly. See 1-Wire for details.

3. Create enable, hysteresis, and setpoint datapoints

Under Datapoints, create three more datapoints without a data source or target. Their values are set by the program or operator.

Enable these datapoints and leave Read only off. Use a positive hysteresis value. The program start event in step 4.1 sets the starting values.

The screenshot shows an intermediate state: enable and hysteresis still have status Unknown, and hysteresis shows 0. All three settings must be valid after the program starts. Datapoint IDs may differ; the following programs use technical names.

4. Create events and control logic

Open Program. Each event can use Blockly or JavaScript as an alternative.

4.1 Set starting values

Create an enabled Program → Start event. In Blockly, use four Set datapoint value blocks to set enable to false, the fan to false, hysteresis to 0.5, and the temperature setpoint to 25.

Alternatively, enter this JavaScript code:

dp.set("luefter_freigabe", false);
dp.set("luefter", false);
dp.set("hysterese", 0.5);
dp.set("solltemperatur", 25);

This example resets these values on every program start. Enable must be switched on deliberately after startup. To retain settings across restarts later, use datapoint persistence and initialize only values for which dp.get does not return a valid value.

4.2 Run the controller on temperature updates

Create an enabled Datapoint → Value updated event with Temperatur as its source. This runs the controller on every successful measurement update, even if the temperature has not changed.

Build the following Blockly logic:

1. In an if/else block, check whether Lüfter Freigabe is true.
2. In its do section, compare Temperature > Setpoint + Hysteresis. If the condition is met, set Lüfter to true.
3. Below it, add a second if block for Temperature < Setpoint − Hysteresis. If the condition is met, set Lüfter to false.
4. In the outer else section, set Lüfter to false.

The inner comparisons have no else branch. This keeps the previous output state inside the hysteresis band. Use Set value so that an unchanged temperature does not toggle the fan on every measurement.

The JavaScript alternative additionally checks for valid numbers and positive hysteresis before comparing temperatures:

if (dp.get("luefter_freigabe", false)) {
  const temperatur = dp.get("temperatur");
  const solltemperatur = dp.get("solltemperatur");
  const hysterese = dp.get("hysterese");

  if (typeof temperatur = "number" &&
      typeof solltemperatur = "number" &&
      typeof hysterese === "number" && hysterese > 0) {
    if (temperatur > solltemperatur + hysterese) {
      dp.set("luefter", true);
    }
    if (temperatur < solltemperatur - hysterese) {
      dp.set("luefter", false);
    }
  }
} else {
  dp.set("luefter", false);
}

If numeric values are missing, this JavaScript variant makes no new temperature decision. If enable is off or invalid, it turns the fan off.

4.3 Respond to operator changes

Create three more enabled events using the same control logic from step 4.2:

These events respond to changes from Home Assistant, for example. The logic reads current datapoint values each time and needs no continuous loop or delay.

Save and apply the program. Start it with I/O & Interfaces active, then check the initialized values and event execution status. See Events and JavaScript for triggers and device functions.

5. Optional: Operation through Home Assistant

Under I/O & Interfaces → MQTT, configure and enable the connection to the shared broker. Then open Datapoints → ⋮ → Home Assistant AutoDiscovery.

Select the five datapoints and use the mapping shown in the screenshot:

Leave the discovery prefix at homeassistant if that is what your installation uses. Enable Automatically enable required MQTT settings, review the changes, and choose Save, apply & publish. This action also applies other pending configuration changes.

After publication, you can display the temperature, activate the controller through Lüfter Freigabe, and adjust the setpoint and hysteresis. Switching Lüfter directly sets the output; local control may change that state again on the next evaluation. Use enable for normal operation.

Setup is described in detail under Home Assistant and MQTT.

Verify operation

Use a 25 °C setpoint and 0.5 K hysteresis. Enable the controller after program startup, for example through Home Assistant. To test without Home Assistant, create a custom event with the following JavaScript code and run it once using Run:

dp.set("luefter_freigabe", true);

To disable the controller, set the value to false. Creating such events is described under Events.

For temperature changes, wait for the next sensor update. The configured read interval polls the sensor every five seconds. Check output feedback and event execution status.

Troubleshooting

Result and extension

IOZER controls the fan using two temperature thresholds. Enable turns the controller on and off, while the setpoint and hysteresis remain adjustable datapoints. Home Assistant adds display and operation to the local controller.