Home automation electronics and SW development - Ing. Pavel Sedláček - Arduino
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Homepage > UNICA 1-wire sensor module > About the module

About the module

What's it about? ...

probably the majority of people, who are thinking about home automation, have come across the question of the optimal placement of enviromental sensors in a room. We want to detect and measure a number of physical quantities – temperature, humidity, lighting, CO2, motion, etc..

If we don't consider strictly ceiling sensors (PIR sensors, smoke detectors or CO2), there is a possibility of placing the sensors into a wall light switch. Temperature-wise it's the ideal distance from the floor (it's always warmer at the ceiling than at the floor). It is also sufficient for measuring, for example, humidity. Last but not least, it can come in handy to measure light intensity in a room as well. All that should be functional at the height of a wall switch.

That was the placement. Now what about the aesthetics? Is it possible to create a „blind“ switch next to the light switch, which would be used to measure required quantities? A few openings in a "blind" switch would be enough for a sufficient airflow. But that would still mean one more module on the wall next to the switch.

Placing the sensors directly into the light switch would be much more aesthetically pleasant. Provided the space around it is sufficient. Firstly, there would be no need for one more "blind" switch on the wall. Secondly, we could use the interconnecting UTP cabel leading to the switch / button on the wall.

That's my theory. Now to business: 

I wanted temperature, humidity and lighting sensors in a switch, with the possibility of using all sensors at once or just some of them. The reason for measuring temperature is obvious, to regulate the heating in the room. Measuring humidity is to regulate ventilation in rooms such as bathroom, laundry room etc. And a lighting sensor together with a PIR sensor would, for example, control lights in hallways that have enough natural light during the day and therefore have no need to be lighted.

As a solution I thought of using Schneider UNICA illuminated wall switch:

This switch has an integrated LED (light-emitting diode), which primarily functions as a position light for the switch. If we dismantle the switch and take out this illuminating component, we are left with enough space to place the sensors in and a slot for sufficient airflow.

Because, for example, Loxone supports the amazing DS2438 circuit by Maxim, which communicates using 1-wire bus and is able to gauge all three sensors (when connected correctly), I have decided to use this particular one.
So, I have created a PCB (printed circuit board) where all components are in SMD (surface-mount device) version and therefore miniature. Then I placed this PCB into the aforementioned space in the switch

Electrical schema and the resultant PCB with the components and sensors:


Possible functions of a fitted UNICA switch:
  1. The 1-wire bus is used to measure physical quantities in a room
    - measuring temperature, humidity and lighting intensity using a DS2438 circuit or measuring temperature using a DS18B20 circuit
  2. Universal signalling LED
    - controled using analog or digital Loxone output
    - colour options – blue, red, white
    - only available in a version without humidity sensor
  3. 1x digital input - only available in a version without lighting intensity sensor
  4. Button's switching contact
    - 24V signal for binary input (e.g. Loxone)


When using the mentioned PCB in a switch to measure quantities, the UNICA switch MUST NOT be used with the standard 230V AC (alternating current) wiring installation. The switching contact can ONLY be used for low 24V DC (direct current) – i.e. controlling the Loxone system binary input.

The resultant module:

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