Design and mill PCB: Easy and Cheap (Fritzing) – Part 2
Starting Project
To start we need a project, I like to create a fast prototype board for my IC, and I like to program with ESP01 with only two wire, so PCF8574 IC a I/O port expander via i2c protocol is my first prototype board.
The input female pin is GND, VCC, SDA and SCL, the dipswitch-03 is for setting address of i2c.
Then there are 8 female pin for I/O (P0-P7) and a Interrupt pin near SDA SCL pin.
You can find library to use in a simple manner the IC here and the guide here. Fritzing project here.
Fritzing: Project
For first you must create your prototype on breadboard.
As you can see the only difference from a “normal prototype board” is that I add a female pin.
I add that because so I have that pins to the PCB schema.
If you want you can create a schema for better comprehension, but It’s not needed.
Fritzing: Start Draw PCB
Than in the third tab you have a scrambled PCB and here we must work.
Positioning is very simple, so I add only some advice.
Fritzing: select correct layout of PCB
For first select a gray PCB and in the right panel select one layer PCB.
Fritzing: Use Jumper to Overlap
Than start to positioning element over the PCB.
Connect element, when you have a overlap you can use a jumper element, you can find It at the end of core parts with some other useful instrument for create PCB.
Fritzing: for Bigger Hole Ring
I need to connect 2 elements but 2 wire is in the middle so you can use a jumper wire to doing that.
Sometime I don’t use jumper wire because I like to create hole bigger than normal.
You can specify size, when I can I create 0.8 0.8 hole (for bigger hole ring).
Fritzing: Set PCB Size to Reduce Waste
The blank PCB that I buy is 7cm x 5cm.
To have a better milling surface I’m going to use a bigger surface with minimal waste so I select a sub-multiple dimensions like 1/2 of the size 3.5cm x 5cm.
Fritzing: Use Bigger Size of Copper Wire
It’s better to create a thick copper wire.
Bigger copper wire is more safe when you are going to mill PCB.
So select copper wire and “extra thick” on panel.
Fritzing: It’s not always need create components
In this project I need a dipswitch 03 but in Fritzing you have 02 and 08, if you want you can create the component or you can overlap 2 of that to create a single dipswitch 03.
Fritzing: some text on PCB
If you want add some text on PCB you can use a text instrument.
Now we create a single side PCB so to write something like second image.
You must select silkscreen bottom, and to have a good readability I think you must set 4mm text height (with autolevel 3mm).
Isolated areas
When making a PCB it is important not to have “islands” or isolated areas because in high frequency circuits can generate electromagnetic fields, so as far as possible they should be avoided, but if you can not avoid them, or eliminate them in milling or placing a hole that can be used to weld a wire to be worn to GND.
90 ° curves
Another aspect that made me notice that the 90 ° angles generate escape currents in the corners, there is a little secret to be able to keep the corners at 90 degrees, but in every corner you have to put a circular pitch, doing so cancel the escape currents.
In Fritzing you can curve the line by using Ctrl button
Fritzing: connect all elements
At the end when you connect all elements and write what you want.
The typical result is in the Image.
Fritzing: generate gerber file
In Fritzing we can export the gerber file from the menu File–>Export–>for Production–>Extended Gerber.
Select a folder and go.
The name of the generated file is quite readable.
Thanks
In the next chapter we will see how to use FlatCam to generate incisions and holes from our Gerber.
