| Visual Cue
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Narration
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| Show title slide
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Welcome to this spoken tutorial on using GSchem to draw a circuit schematic.
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| Show Slide-2 listing Learning Objectives.
Make bulleted text blocks appear one-by-one by pressing Enter.
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After completing this tutorial, you will be able to
- create a circuit schematic using GSchem.
- generate the netlist from it for simulation using Ngspice.
Another tutorial explains how to make a printed circuit board from the schematic.
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| Show Slides-3 and 4 listing software used.
Make bulleted text blocks appear one-by-one by pressing Enter.
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In this tutorial I have used
Snapshot Version of Zenwalk GNU Linux which is a free operating system derived from Slackware, available at www.zenwalk.org.</tt>
Instead of this you may also use Ubuntu GNU Linux..
gEDA Suite Version 1.7.2 available at geda-project.org.
To install gEDA Suite, use Xnetpkg in Zenwalk. Or use Software Centre in Ubuntu.
To understand how to install packages in Ubuntu, refer to Ubuntu Spoken Tutorials.
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| Show Slide-5 listing prerequisites.
Make bulleted text blocks appear one-by-one by pressing Enter.
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To understand this tutorial, the pre-requisites are –
- Circuit theory.
- Analog and digital electronics.
- Skills in operating a GNU Linux system.
- Basics of SPICE.
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| Switch to the Zenwalk desktop.
Right-click on the desktop.
In the desktop pop-up menu choose Applications →Science →gEDA Schematic Editor.Click on gEDA Schematic Editor.
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On a Zenwalk system, right click on desktop to get the desktop pop-up menu.
Start GSchem by clicking on the link to gEDA Schematic Editor in the Applications Menu.
Ubuntu users please click on Applications menu and choose gEDA Schematic Editor.
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| Display the GSchem screen.
Move cursor to Close button.
Point to the rectangular area.
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This is the opening screen of GSchem.
You can close the status dialog box by clicking on the Close button.
GSchem belongs to gEDA Suite of programs.
It is used to draw schematics and symbols.
Schematic should be drawn within this area.
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| Click on 'View' and point to the pull-down menu.
Point to the keyboard short cuts options.
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Clicking on View, displays this pull-down menu.
Keyboard short cuts or hot keys to perform different operations are given in this menu.
It is much faster to use hot keys instead of operating the mouse.
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| Type 'vl'.
Point to the light color scheme in the drawing area.
Type 'z' to demonstrate zoom in.
Type 'Shift+z' to demonstrate zoom out.
Show zoom-in and zoom-out with mouse wheel also.
Type 've' and demonstrate.
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For example, type vl on the keyboard to get light color scheme for drawing area.
Type z to zoom in and Shift+z to zoom out.
We can also zoom in and zoom out by turning the mouse wheel up and down.
Finally zoom extents by typing ve.
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| Display Slide 6 showing the circuit.
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This is the circuit we propose to simulate using Ngspice.
In this circuit we need to find Va, and the power delivered by this current controlled voltage source.
We also need to verify Kirchhoff's Voltage Law and Kirchhoff's Current Law.
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| Display Slide 7 showing the schematic in which dummy voltage sources have been inserted.
Point at reference node.
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In Ngspice, a D.C. voltage source of 0 V, known as dummy voltage source, is used as an ammeter to measure current.
We insert them in branches where current has to be measured.
We also need to indicate the reference node with respect to which all other node voltages are measured.
Without this SPICE simulation does not work.
To create this schematic, we need the symbols of current source, voltage source, resistor, current controlled voltage source, and ground.
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| Switch back to the gSchem window.
Click on Add and point to the pull-down menu.
Point to the various options as you narrate.
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Clicking on Add displays this pull-down menu.
There are options in this menu to place a component, a net, a bus, an attribute, text. These are used to draw the schematic.
Options to draw line, box, circle, arc, pin, and picture are useful while drawing symbols.
When the required symbol is not available, we have to create it.
Symbol creation is explained in another tutorial.
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| Point at Add Components button.
Type i.
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To add a component to the schematic, we can click on this button,
or we can type the keyboard short cut i.
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| Click on small triangle to open a library.
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When we type i, this dialog box appears listing all the libraries.
We can open a library by clicking on the small triangle beside it.
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| Type resis in the filter field.
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If we do not know in which library the required device symbol is present,
we can type the initial few letters of the name of the device in the filter to locate the symbol.
For example, to find resistor symbol, we can type “resis” in the filter to list related symbols as shown here.
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| Click on resistor-1.sym.
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We can select resistor-1.sym. Its preview is shown.
This symbol has reference descriptor indicated as Refdes R?
In SPICE, single letters are used to specify different components.
For example, R refers to resistor,
V refers to a voltage source,
I refers to a current source,
H refers to a current controlled voltage source and so on.
Do not remove the reference descriptors as they are needed for simulation.
More information about reference descriptors of devices is given in the tutorial on Ngspice.
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| Click on drawing area to place the resistor.
Right-click on the drawing area.
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Drag the resistor symbol and click in the drawing area to place it.
Observe the Refdes R?
Right click in the drawing area to deselect the symbol.
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| Type volt in the filter field.
Select voltage-3.sym.
Click on the drawing area.
Right-click on the drawing area.
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Similarly, select the D.C. voltage source symbol and place it in the drawing area.
Observe the Refdes V?
Deselect by right clicking in the drawing area.
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| Type ccvs in the filter.
Select ccvs-1.sym.
Click on the drawing area.
Right-click on the drawing area.
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Select the current controlled voltage source and place it in the drawing area.
Observe the Refdes H?
Deselect by right clicking in the drawing area.
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| Type cur in the filter.
Select current-1.sym.
Click on the drawing area.
Right-click on the drawing area.
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In the same way, place the current source symbol also in the drawing area.
See the Refdes I? for the current source.
Right click to deselect.
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| Type gnd in the filter.
Select gnd-1.sym.
Click on the drawing area.
Right-click on the drawing area.
Click on the Close button of library.
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Place the ground symbol in the same way.
Observe there is no Refdes for this symbol.
Deselect by right clicking.
We should note that there are also components in libraries which cannot be used in SPICE but which are needed for making the printed circuit board of the circuit.
Now we have placed all the required symbols.
So, click on the Close button to close the library.
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| Click on Select Mode button.
Click on a component symbol in work space.
Type c and drag copy.
Select another component.
Type er to rotate it by 90 degrees.
Select another component.
Type ey and drag to show multiple copies.
Right-click to deselect multiple copies.
Press Del key to delete unwanted components.
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We can select a component in the workspace by clicking on it in the select mode. This is the select tool.
We can make a copy of a component by first selecting it, and then typing c, and then dragging the copy.
After selecting a component, if we type er, the symbol is rotated by 90 degrees.
We can make multiple copies of a selected symbol by typing ey.
We can delete a component by pressing Del key after selecting the component.
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| Click on Edit.
Point at all the editing commands in the pull-down menu.
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All editing commands are listed in this Edit pull down menu.
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| Using select tool double click on resistor symbol in the drawing and enter its value.
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To add value of a resistor, double click on the resistor symbol.
Under Add Attributes select Value in the pull-down menu.
Enter value of the resistor in the space provided with the required scale factor used in SPICE.
Select Show Value Only in the visibility pull-down menu, and click on +Add button.
Click on Close.
Now the value is added to the resistor.
To change the value of a resistor, double click on its value,
type new value, and click on Ok button.
Similarly values for all other components can be entered.
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| Make copies of components as required.
Place them properly.
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After making copies of components
and entering values and placing them,
the schematic will be like this.
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| Type n.
Connect components.
Right-click to stop connecting.
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Type n to start Add Nets mode. In this mode we can make connections.
In networking mode a small circle appears as shown.
We can cancel networking by right clicking.
After making all connections the schematic will be like this.
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| Click on Attributes.
Click on the Autonumber option.
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Clicking on Attributes gives this pull-down menu.
In this menu click on Autonumber Text.
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| Select Autonumber Text in: Current Page.
Click on Apply.
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In the Autonumber Text dialog box,
select search for Refdes=*, autonumber text in Current page,
starting number 1, and click on Apply.
This numbers the components automatically. Click on Close.
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| Type Ctrl+a.
Drag the schematic to centre of drawing area.
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Type Cntrl a simultaneously on your keyboard to select the entire schematic
and drag it to the centre of drawing area as shown.
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| Click on Add Text button.
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Clicking on Add Text button opens this box to enter text.
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| Type VERIFICATION OF KIRCHHOFF'S LAWS in the text entry field.
Click on Apply.
Drag the text beside TITLE.
Click on Close.
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Type VERIFICATION OF KIRCHHOFF'S LAWS and click on
Apply and drag the resulting text line beside TITLE as shown
and click to place it there.
Click on Close to close the Text Entry box.
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| Choose Select mode. Double click on the wire to the left of V3.
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In select mode,
double click on the wire on the left side of V3.
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| Type a as netname.
Select Show Value only.
Click on +Add button.
Click any where on the drawing area.
Click on the name entered.
Drag it to correct position.
Similarly add b as label to the right node of V3.
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Add a as netname, select Show Value only, and click on +Add button.
Move the netname to proper place.
Similarly, add name b as for the node on the right of V3.
This is the completed schematic.
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| Type fs.
Give file name as kvlkcl.sch.
Choose appropriate directory to save.
Click on Save.
Quit gEDA Schematic Editor.
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We need to save this.
Type fs.
Give the file name as kvlkcl.sch.
Select appropriate directory to save and click on save.
Now the file is saved.
We need to generate the SPICE netlist from this for simulation.
Close Gschem editor.
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| Right-click on desktop.
Click on terminal.
Type cd /path/to/kvlkcl.sch
and press Enter.
Type the command
gnetlist -g spice-sdb -o kvlkcl.cir kvlkcl.sch
and press Enter.
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Open terminal and go to the directory where the kvlkcl.sch is stored.
Type the command
gnetlist -g spice-sdb -o kvlkcl.cir kvlkcl.sch
and press Enter.
This generates the SPICE netlist file kvlkcl.cir in the same directory.
If your file names are different change accordingly.
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| Open the file kvlkcl.cir in Geany.
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The netlist file can be opened in any text editor like Geany.
This file can be loaded in Ngspice to conduct simulation.
More details about simulation commands are explained in the tutorial on Ngspice.
This completes the tutorial.
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| Summary Slide-8
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In this tutorial we have learnt
- How to create a circuit schematic using Gschem.
- How to generate the netlist from it for simulation using Ngspice.
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| Assignment Slide-9
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Draw schematic to simulate this circuit and generate its netlist.
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| Slides 10
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Watch the video available at the following link.
It summarises the Spoken Tutorial project.
If you do not have good bandwidth, you can download and
watch it.
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| Slides 11
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The Spoken Tutorial Project Team
- Conducts workshops using Spoken Tutorials.
- Gives certificates to those who pass an on-line test.
- For more details contact contact@spoken-tutorial.org.
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| Slides 12
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Spoken Tutorial Project is a part of the Talk to a Teacher project.
It is supported by the National Mission on Education through
ICT, MHRD, Government of India.
More information on the same is available at:
http://spoken-tutorial.org/NMEICT-Intro
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| Slide 13
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This is R S Ananda Murthy from S. J. College of Engineering, Mysore, signing off.
Thank you for joining.
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