SINGLE-POLE SINGLE-THROW SWITCH WITH SOFTWARE SIMULATOR
Read our book:
In the previous lesson we have analyzed a simple power supply circuit for a lamp. It is evident that this circuit does not allow any control on the state of the lamp. In other words, if we intend to turn the lamp off, we must necessarily disconnect the voltage generator.
In this lesson, we will deal with controlling the state of the lamp from a command point using a device called “single-pole, single-throw switch” or briefly “SPST switch”.
If you live in the USA, electricians are much more likely to talk about two-way switches, while if you live in Europe, you will hear electricians talking about one-way switches.
There is a long debate on the Internet about the origin of this terminology and about the best name to assign to these switches.
Our opinion is: if you want to be precise and don’t want to be misunderstood then use the term SPST switch, but keep in mind that the other names are frequently used in technical jargon.
Let’s focus on the use of the SPST switch. This electrical device is widely used in electrical systems, therefore we will simulate the operation of the SPST switch thinking of its typical use in the room of a home.
To this aim, we take the circuit drawn in the previous exercise which is reproduced, for your convenience, in the following figure.
We will manipulate this circuit in order to make all the changes that allow you to control a lamp through a single-pole single-throw switch.
Figure 69: Circuit designed in the previous lesson.
The switch must be inserted between the battery and the lamp in the position indicated by the red arrow in Figure 70. We must first create some space to allow the switch to be inserted. So let’s take this opportunity to learn some other Proteus features. Specifically, we want to move the lamp to the right as shown in Figure 71. To do this, move the mouse pointer closer to the lamp as shown in Figure 72 and click once with the mouse left button. As shown in Figure 73, a cross will appear indicating the possibility of being able to drag the selected device. Keeping the left mouse button pressed, we drag the lamp to the right, as shown in Figure 74. The lamp must be dragged in order to create enough space for the insertion of the SPST switch (Figure 75). We then release the left button when we have reached a layout similar to that shown in the example screen in Figure 76.
Figure 70: Indication of the point where the circuit must be modified to insert a single-pole single-throw switch.
Figure 71: Indication of the dragging direction to be applied to the lamp to create the space in order to insert the SPST switch.
Figure 72: First step for dragging the lamp.
Figure 73: Second step of the lamp dragging procedure.
Figure 74: Third step of the lamp dragging procedure.
Figure 75: Fourth step of the lamp dragging procedure.
Figure 76: Final appearance of the worksheet once the lamp has been moved to the right at a sufficient distance from the battery in order to allow the insertion of the switch.
In order to allow the switch to be inserted in the circuit, we must now remove the wire that connects the positive pole of the battery to the lamp (indicated by the red arrow in Figure 77).
Figure 77: Indication (red arrow) of the electrical connection to be removed for the insertion of the single-pole single-throw switch.
—
To do this, we click with the right mouse button on the wire to be deleted (Figure 78) and select the “Delete Wire” item.
Figure 78: Selection of the “Delete Wire” item to delete the electrical connection indicated in red.
At this point, as shown in Figure 79, the circuit has been prepared for the insertion of the switch.
Figure 79: Appearance of the worksheet after having deleted the electrical connection between the positive pole and the lamp.
Let’s access the component library by pressing the letter “P” or equivalently from the “Library” menu we can click on the item “Pick Parts” (Figure 80). Let’s select the category “Switches & Relays” (step 1 of Figure 81) and among the various switches available, we must select the one with the code “SW-SPST-MOM” (step 2 of Figure 81). An equally valid alternative would be the device with the “SW-SPST” code, which is not used now but we will be used later in the lesson.
Read our book:
The description of the “SW-SPST-MOM” device tells us that it is an “Interactive SPST Switch (Momentary Action)”. The terms of this description will be clearer throughout this lesson. For the moment it is important to note that it is an interactive switch that therefore makes us think about the possibility of operating it interactively during the simulation. The device symbol (point 3 of Figure 81) clearly shows that it is the typical switch used in the electrical systems of our homes. Let’s recall that this switch is indicated with the acronym SPST which stands for “Single Pole Single Throw”.
The term “Single Pole” evidently refers to the fact that the switch is single-input, as indicated by the blue arrow in Figure 82.
The term “Single Throw” refers to the fact that this switch, in correspondence with the only available input, is able to control a single circuit or in other words, it has only one output for the available input, as indicated by the blue arrow of Figure 83.
Well, made this necessary clarification, we can press the “OK” button and proceed. The selected switch will appear in the worksheet (Figure 84) and we can therefore proceed to its connection to the battery and to the lamp, as indicated in Figure 85. We will not explain again the procedure for drawing wires since these steps have been widely addressed during the previous lessons.
Figure 80: Starting the procedure for the insertion of the single-pole single-throw switch in the worksheet.
Figure 81: Selection of the switch suitable for the simulations to be carried out in this lesson.
Figure 82: Analysis of the name and symbol of the SPST switch.
Figure 83: Further details on the name and symbol of the SPST switch.
Figure 84: Appearance of the worksheet after the selection of the SPST switch from the Proteus device library.
Figure 85: Appearance of the worksheet at the end of the drawing of the electrical connections between the single-pole switch and the rest of the circuit.
Let’s start the simulation of the circuit just drawn, by pressing the appropriate button at the bottom left of the worksheet and, as expected, the lamp will be turned off since the switch is open (see the following figure).
Figure 86: Starting the simulation. It is noted that the switch is open and therefore the lamp is turned off.
Now let’s try to operate the switch by hovering the mouse pointer over the control point (Figure 87) represented by the red circle with a black background and then clicking once with the left button. The switch will be closed (Figure 88) and as expected the lamp will turn on since closing the switch creates an electrical connection between the positive pole of the battery and the lamp.
Figure 87: Flipping the switch by clicking with the left mouse button on the black and red circle (see red arrow).
Figure 88: Closing the switch which turns the lamp on.
We can now open again the switch to check if the lamp will turn off. As shown in Figure 89, what is expected in theory occurs in simulation and we can therefore consider successfully completed the simulation carried out with Proteus.
Figure 89: Reopening of the switch and consequent turning off of the lamp.
Read our book:
