What is (and what is it used for) a "clean contact" actuator in home automation

3 minutes of reading

The "clean contact", in home automation, it is one of the cornerstones to succeed, often and willingly, in to domotize household appliances, components, systems, various elements that, by nature, they wouldn't be home automation.

But what exactly are they? clean contact it's a clean contact actuator?

We will try to explain it in words as simple as possible; we don't need electrical engineering experts, who will find this board perhaps trivial, but we hope thelumifor those who are dry with certain notions.


If between two poles that they present one electrical potential difference (measurable in volts) yes applic load (eg a light bulb), the current will begin to circulate in the circuit; in case the current is continues the two poles will be positive and negative, while in case of current alternating (the home 220v) will typically be one phase and one neutral.

A type “home automation actuatorintelligent switch", Like the Sonoff Basic, it has two phase / neutral poles at the input and the same number of poles at the output, always phase / neutral. When we operate it, it "delivers" tension to outgoing garments, therefore if, for example, a light bulb is connected to the poles, it will obviously light up.

Sonoff  SV

A "clean contact"Is nothing but a pole that does not present no difference in electrical potential against a second pole usually called "common". This contact is used, in pairs with his "common", to command the most disparate functions of the most disparate electronic components.

Il clean contact may be entry or exit; also it can be normally open (NO) o normally closed (NC).

Let's clarify means a simple example.

Many boilers for independent heating are equipped with a "normally open input clean contact". This means that these boilers have two poles which, when the boiler needs to be produke heat, they must be shorted between them. In the event of a "normally closed input clean contact", for protough heat the two poles should be disconnected among them.

A classic thermostat with "clean output contactneed probefore this, or to control a boiler controlled by "clean contact on entry“: It short-circuits or disconnects the two poles on the basis of the temperature detected in the environment and the proman proprogramming. In essence, a thermostat is nothing but a kind of switch that short-circuits or disconnects two poles no tension between them.


We said that the Sonoff Basic is an actuator capable of delivering on command a voltage at the output poles. However, as is known, the Sonoff Basic lends itself to a physical change which allows the actuator to transform and become an actuator with clean output contact, or by connecting (to its outputs) the two poles a clean contact (incoming) of any device, it is capable of short circuit them / disconnect them on command without introducing any voltage profirst, resulting in the planned action. Connected instead of one of the above thermostats, can take their place (we have approthis reason blendednamento in this projet).

An alternative is to use a Sonoff Mini (always modified) or, without having to change anything, the Sonoff 4ch PRO offers factory this functionality: in fact has four clean contact outputs such as to command as many enter clean contact.

The importance in home automation

ITEAD Sonoff 4ch PRO clean contact connection
an example with Sonoff 4ch PRO

Since a home automation actuator a clean output contact in fact it is similar to a mechanical switch / a button (the button at the end is nothing but a mechanical switch unable to remain active when released), it goes without saying any appliance or components that presents one or more clean contacts on entry to control its functions it can be "domotizzato" through this type of actuators.

The power button on the washing machine, for example, rappsents a clean contact entry: if in its place (at its ends) I connect the outputs of an actuator to clean contact, then I will be able to control its switching on via home automation.

Similarly, the buttons on a remote control they are also similar to revenue a clean contact: when I connect them to the exits a clean contact of an actuator, I can "press the keys" by controlling their respective functions from home automation (you see projet of approelucidation).

The range of possibilities that opens up the existence of clean-contact output actuators it's very wide: gates, electric pumps, alarm systems, remote controls and much, much more: all components controllable via home automation via clean contact.

Projets inDomus

Here are some procastings related to this type of actuator.

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