Technical details on Switch input

1. offizieller Beitrag

    Hi -

    Just getting started with my first Shelly device. So far I'm really impressed with the size, functionality, price, etc.

    I would like to understand the SW input in more detail. All documentation I can find indicates that this input should be left floating (disconnected) for logic zero or brought to the same level as the L input for logic one. But I would like to understand the operation in more detail.

    Is SW a digital input with a specific threshold voltage? If I am powering the SW with an external signal (from a sensor or raspberry pi) can I drive the input high with the other device's digital output, or must it truly be connected with a relay to the Shelly power supply voltage, regardless of whether that voltage is 120V, 12V, 40V, etc.

    Thanks:!:

    • Offizieller Beitrag

    the inputs are preloaded with half the supply voltage (at 230V ~ 115 to 120V). This serves to be able to switch the Shellys with "L" (230V) as well as with "N" (0V).

    Likewise, only the phase that is responsible for supplying the Shelly should be switched. 400V are deadly for the Schelly ....

    If you want to switch via reed contacts or with other nice things take a look at the new option using the add-on (only applies to Shelly and Shelly 1PM)


    Anschlussschemen Temp-AddOn

    Welcome to the forum!

    Your assumption is not correct. A Shelly’s SW input is triggered by current, not by voltage: A very small current (about 34μA), flowing from SW to pin L, activates the signal. With mains voltage, this leads to the effect that input triggers both with L and N potential. With small voltage supply, this isn’t true. As a thumb rule you may assume that input is triggered with the potential at pin L - which is in general ground potential.

    You may find some insight in the inner guts here and the included links (unfortunately in German language):

    Thema

    Konstruktive Lösungen für einen Widerstand an Klemme SW/IN(x)

    Mehrere Mitglieder des Forums haben unabhängig voneinander und empirisch eine Methode gefunden, um mit Shellies die Abnahme des Schaltzustandes an Schaltern mit angeschlossenen Verbrauchern zu ermöglichen, ohne Zwischenrelais oder ähnliche Schaltelemente nutzen zu müssen. Das waren - ohne Anspruch auf Vollständigkeit! - die Mitglieder @martinjuhasz , @bukowski und @Mr Fawlty .

    Diese Lösungen sind in den Beiträgen

    Shelly durch Bewegungsmelder oder Schalter/Taster schalten…
    thgoebel
    2. September 2021 um 18:57

    „Habt Geduld. Alle Dinge sind schwierig, bevor sie einfach werden!“ (aus Frankreich)

    „Nothing in life is to be feared, it is only to be understood.“ (Marie Curie, 1867-1934)

    „Es reicht nicht“, rief Schiller, „Gedankenfreiheit zu fordern, man muß auch denken können, sonst fordert man Gedankenlosigkeitsfreiheit und die ist die Freiheit zur Dummheit, welche wiederum die schlimmste Unfreiheit überhaupt ist!“
    (Aus „Besuch aus Weimar“ von Gert Heidenreich, Schriftsteller, *1944 in Eberswalde)