My Hobbies - Circad Course - Lesson 1
Electric Scheme Creation

Parabola

Barra Colore


Circad is the perfect program to obtain a pcb starting with the electric scheme of an electronic circuit. With these lessons you'll learn to use Circad at the best level. To do this you'll realize the circuit board or PCB of the circuit beside.

To draw the electric scheme is necessary to create a schematic file type, that have the .SCH extension. Circad can use many different files format, including AutoCad, text file, etcetera. Every type of file have diffent charateristics that depends by the extension!. In fact, Circad use a file in a specific mode that depends by the extension, for example linking library file. So, isn't possible to use custom extension, but it's necessary to use the reserved extensions types.


When you make an electric scheme and the associated PCB, many kinds of file are used, linked togheter like below:

.SCH
Electric Scheme
> .NET
Components & Wiring
> .PCB
PCB Board Layout
> .BOM
Components List
/\.LIB
Schematic
Components
\/.LOG
Error on the .SCH file
/\.LIB
PCB
Components

Now we make the schematic file, that have the .SCH extension and that we'll call TUTOR1. Select the File menu, then the New File option ... or FW. Insert the directory where you want to save the file. Circad will ask to select a template for the file. A template is a model for a circuit. We must create a .SCH type file, then select "Schematic Files" = Size A . The "A" format corresponds to an A4 sheet.

The A4 format is the best you can select. If you are an engineer with a A2 plotter device... then select the other sheets formats. If your circuit is very complex remind that Circad is able to manage electronic schemes splitted in many schematics files.



Once you've select the template, Circad will display a save form, then select the directory and the name of the file you want to create. In the Circad Windows version you can use more than 8 caracters.

Using the "Export filter" option menu you can select the file format, but if you don't need to reimport Circad '98 files in Circad 3.8, use the default option.

Attention! Circad 3.52 and 3.8 DON'T recognize the Circad'98 file format, but Circad '98 is totally compatible (only to read) with these versions!

To save the file, select the Esempio subdirectory, created with the special icon of the form, but you can select any directory you want. All the instructions I've explained above are the same of FW + "Schematic Files = Size A" + C:\Programmi\Circad98\Esempio\Tutor1.SCH (if you have installed Circad in the Programmi\Circad98 directory) ... but we are only at the beginning of the course...

After you've created the TUTOR1.SCH file you can customize or remove the information automatically added by Circad, for example using the option to edit lines or texts, like ET, EX or GT. The information displayed are stored in the files with the .T?? extension, located into the CIRCAD.TPL subdirectory. Then, if you modify the template file, every time you'll create a new file, only the information included (text, lines, etc.) in the relative template will be added, without to re-edit the new file.

At the left bottom of the screen you can see the actual screen coordinates (in inches) of the cursor, the grid value and the active layer. The coordinates can be displayed in two modes: absolute or relative (indicated with an asterisc). The mode switching is done by simply pressing SP for every mode change. The relative coordinates will be useful to mark an origin point different from the default origin (left bottom of the draw area).

> SP >
> SP >

The snap grid value can only be set to the value assigned by the user. For example, with the option Circad will display the grid form. If you insert " 5,25,100 " you specify that the mouse will move only with a step of 5, 25 or 100 mils that is 0.005, 0.025 or 0.1 inches. Every time the user will use SG Circad will display a form to select the new grid value.

The coordinates can be displayed only in inches. To evaluate the pcb dimensions of your board you can print the file TARATURA.PCB (12k .zip) for Circad Dos/Win that include many different reference and calibrating tools and a rubber converter centimeters/inches.

Conversion
Table
Inches
inchs
Centimeters
cm
Mils of inch
mils
Millimeters
mm
\/ \/ \/ \/
Inches
inchs
< cm / 2.54 mils / 1000 mm / 25.4
Centimeters
cm
< inchs * 2.54 (mils / 1000) * 2.54 mm / 10 ...
Mils of inch
mils
< inchs / 1000 (cm / 2.54) / 1000 (mm / 25.4) / 1000
Millimeters
mm
< inchs * 25.4 cm * 10 ... (mils / 1000) * 25.4


Another important thing of Circad is about the layers use. The layers are used to have every element you see on the Circad draw area (text, lines, arcs, pads, etc.) into the right layer. For example, the lines used to make component shape must be assigned to the "symbol" layer, but the lines used to connect two components must assigned to the layer "signal". The layers names depends by the file you are using. So, a schematic file like TUTOR1.SCH will have the layer Signals, (where Circad stores all the electric wirings). A .PCB file doesn't have this layer, but is will contains, for example, the Bottom Copper layer (Soldering Copper Side) and the Top Copper layer (Components Copper Side). With the option SL it is possible to customize the name, the color and the type of every layer. The active layer is selected by pressing the "-" e "+" keys of the numeric keypad.



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