CONVERT A LIGHT POINT CONTROLLED BY CROSSOVER SWITCHES INTO A SMART CIRCUIT
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Welcome to the NPR Online Technologies Home Automation course.
In this lesson we will deal with the concepts that allow us to convert an ordinary circuit that controls a light point from three or more different positions into a smart system. For this purpose we will use the Sonoff Mini and in particular we will use the R2 version and we will also assume that the system is based on the use of crossover switches.
We remind you that the crossover switch is an electrical component consisting of four terminals which for greater clarity we have marked with the labels IN1, IN2, OUT1, OUT2.
As shown in the figure, the crossover switch can assume two positions. In the left representation we have that the OUT1 terminal is connected to the IN1 terminal, while the OUT2 terminal is connected to the IN2 terminal. The representation on the right shows the second state that can be assumed by the inverter, where it is observed that this time the OUT1 terminal is connected to the IN2 terminal while the OUT2 terminal is connected to the IN1 terminal. We therefore note that in this second position there is an inversion of the contacts from which the crossover switch takes its name.
Other names for this switch are intermediate switch and dual-pole double-throw switch. The name intermediate switch will be clarified in the next figures. Concerning the dual-pole double-throw switch it refers to the fact that the device has two inputs as indicated by the blue arrows in the following figure. The term “Double Throw” refers instead to the fact that in correspondence with each input the switch has two contacts or outputs as indicated by the two red arrows.
It should be noted that the use of the terms “In” and “Out” to identify the various terminals is purely indicative since the symmetry of this component allows the input contacts to be exchanged with the output contacts without altering the operation of the device itself .
Let’s continue this lesson by briefly summarizing the operating principle of a circuit capable of controlling the same light point from three or more different points using crossover switches. The typical circuit solution is based on the use of the diagram shown here. As you can see, it is composed of two SPDT switches at the ends and an crossover switch at the center. The left switch (SPDT#1) is connected to the live wire while the right switch (SPDT#2) is connected to the bulb. The two SPDT switches are then connected to each other by means of a crossover switch. This also clarifies why crossover switches are also called intermediate switches. Returning to the analysis of our circuit, we note that the connection to live wire is interrupted at the second SPDT switch and therefore the light bulb is off since it is not powered by the live conductor.
Coloriamo in verde il collegamento di fase per maggiore chiarezza.
When we go to flip one of the three switches, for example the first SPDT switch, the connection to live conductor is not interrupted and therefore it manages to power the bulb which consequently turns on, also considering that its second terminal is connected to the neutral wire.
Again we color the live wire connection green for greater clarity.
If we now try to flip the intermediate switch, this as expected will invert the connections between inputs and outputs and consequently the connection to live conductor will be interrupted at the second SPDT switch. Therefore the bulb will not be powered by the live conductor and will be turned off.
It is clear that, in such conditions, it will be sufficient to flip one of the three switches to restore the connection to the live conductor. As an example, we flip the second SPDT switch and note that this allows us to create a connection capable of connecting the bulb to the live conductor and therefore this will turn on.
Also in this case we color the connection that powers the bulb green. From these simple analyzes we note that given the perfect symmetry between inputs and outputs of an intermediate switch, we can safely exchange them without altering the circuit. Obviously this exchange must take place for both the output and input contacts.
In this figure we have in fact exchanged the inputs with the outputs of the intermediate switch and it is evident that from the circuit point of view nothing has changed. Different is the case where we make connections in which we exchange a single input with a single output. In this case the circuit will not work properly.
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Before concluding the lesson on intermediate switches, we would like to point out that in the case of more than three control points, it is sufficient to add other intermediate switches between the two SPDT switches. We leave to the most interested the simulation of all possible combinations to ensure that the circuit is able to operate as desired. In particular, it will be necessary to verify that the circuit is able to change the state of the light bulb at each switching of any switch. It is noted that the use of SPDT and intermediate switches requires the use of a pair of wires necessary to connect them together. This in some cases can be quite expensive and for this reason this approach is generally adopted in cases where up to three or at most four control points are required. When, on the other hand, more than two or three control points are required, relays are used which allow a more elegant and more compact construction and in some cases even safer. Safer because the operating point, which as we will see is the button, can work at low voltage and consequently accidental contacts with the connections would not involve any risk for the person. In fact, we remind you that the circuits we are analyzing are powered with a voltage of 230 V in alternating current which can be very dangerous and even fatal in the case of accidental contacts.
As anticipated, the goal of this lesson is to transform the circuit just analyzed into a smart circuit, where alongside the manual functionality there is the possibility of controlling the switching on of the light bulb using a smartphone and a Wi-Fi connection. For convenience we report a circuit with three control points, but as already mentioned this circuit can be extended to any number of control points.
To make this circuit smart we will use a Sonoff Mini device in the R2 version.
In the lesson dedicated to SPDT switches we have already extensively dealt with the operation of the Sonoff Mini R2. In that lesson we also analyzed the connections needed to convert an ordinary circuit into a smart circuit in such a way that in addition to keeping the functionality of the ordinary circuit unchanged, it manages to integrate the control functionality via smartphone. The same connection scheme can also be adopted in the case of a circuit with one or more intermediate switches.
In fact, in this figure it can be seen that in the case of one or more intermediate switches, the connection diagram to the Sonoff Mini R2 once again requires that the common terminals of the two SPDT switches are connected to the Sonoff terminals S1 and S2. Therefore the connections of the intermediate switch(es) are not altered with respect to the original circuit. As observed, the circuit diagram just illustrated is completely equivalent to that illustrated in the lesson dedicated to SPDT switches and therefore please refer to that lesson for the details on the connections and installation of the Sonoff Mini in a real system. Let us remember once again that for convenience we have reported in this figure a circuit with three control points, but as already said previously, this circuit can be extended to any number of control points.
Well, we’ve come to the end of this lesson. If you have carefully followed our instructions, you will be able to convert an ordinary control circuit of a light point controlled by crossover switches into a smart solution. For those wishing to learn more about these issues, we suggest accessing our playlists and our website npronline.tech/en. To help grow our initiatives, you can help us with a like, by subscribing to our channel or even by sending us comments and sharing this content with your friends. Thanks for your attention and … see you next time!
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