PCB design | Circuit board design | PCB Design for IoT Plant

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 PCB design | Circuit board design | PCB Design for IoT Plant

Always when starting the journey to the maker world, one of the first things that you have to learn is to understand and design circuits. After all, only then can we bring our ideas to life and interact with the “real world”, right? And, In this context, one of the first things we have contact with is the protoboard, a platform for prototyping very useful and versatile hardware. So in this article I will discuss with details about PCB design or circuit board design, However, the protoboard leaves something to be desired when it comes to the application of circuits in more hostile environments and real applications / outside our laboratories, that is, when things are more serious and more consolidated the prototype is required. Therefore, the next step in a project (after being validated on a protoboard, of course) is to have a PCI - PrintedCircuit Board (or,, PCBPrinted Circuit Board ), so you can go out into the field without fear (and, in addition, give your project a more professional look).

Circuit board design
Circuit board design


And this is exactly what this series of posts will teach you: how to assemble your own printed circuit boards, based on our Planta IoT project. That's right: the IoT Plant project will have its own board and the best: everything is free for you to edit and make any changes you want! You can also choose to use already perforated plates, such as perforated phenolite or double-sided perforated plates , available at the FILIPEFLOP store.

Printed Circuit Boards - what are they?

If you are just starting out in the maker world, this may be a natural issue at this point in this post. In a very simplistic way, a printed circuit board or PCB can be defined as a piece of rigid insulating material (usually phenolite or fiberglass, generally rectangular in shape) that contains layers of circuits designed in conductive material (copper), thus forming a “circuit sandwich”. On the bottom and top surfaces of this board, the electronic components used in the circuit in question are welded.

As an example, there are all the “little signs” that we have, including Arduinos. Each layer of conductive material / circuit is called a Layer, the more complex the circuit, the more Layers will be needed to make your Printed Circuit Board.

Circuit board design
Circuit board design

 

Multi-colored Printed Circuit Boards

In addition, in summary, there are other important elements in Printed Circuit Boards:

  • Mask / Silk : they make it possible to color the Printed Circuit Boards (in blue, green, black, white, red, etc.) and place inscriptions on them. This is a very important layer, both aesthetically and in terms of information about the circuit to be assembled (component codes, values, polarization, etc.).
  • Holes layer : this is a “layer” used in the development of Printed Circuit Boards that contains information about each hole to be made in the board, from the positioning and diameter of each hole to the amount of conductive material to be placed on the board. around each hole.

Making a simple analogy:

  • Instead of protoboards, there are copper surfaces (layers, or Layers )
  • Instead of points for connecting the components, you have the holes of a PCB
  • Instead of wires and jumpers, there are the tracks of a printed circuit.

It is also important to note that not all PCB factories have the same manufacturing technologies. That is, the more complex (more Layers, shorter trails, smaller holes, etc.) a board is, the more restricted the range of manufacturer options is (and the more expensive it is to manufacture, as a result).

What to use to create a PCB design or circuit board design? 

Nowadays, luckily there is several software available for this task, being both paid and extremely powerful software as well as free and open-source software. PCB design or circuit board design is to cite some examples, we have:

  • Eagle
  • Altium
  • Proteus PCB Designer
  • ZenitPCB
  • KiCad EDA

For our series of posts and development of PlantaIoT Board, the KiCad EDA software was chosen (called in the articles only KiCad). The main reasons for the choice are: it is free, open-source, multi-platform software (runs on Linux, Windows and OS X), user-friendly interface and widely used by the community (there are many tutorials on the Internet, including in Portuguese , which facilitates learning). Experienced readers will immediately remember the homesick Eagle (one of the only free options with possible limitations a few years ago) when using KiCad.

Note: if you, like me, use Ubuntu (in my case, version 16.04 LTS), KiCad is already included as one of the packages in the standard repositories. This means that you can download it directly from the terminal.

What is possible to do with KiCad?

The answer is simple: all stages of PCB development. In other words, this tool allows you to develop your PCB from the design of the schematic circuit to the generation of Gerber Files (we'll see what that is in detail throughout the series, don't worry). In summary, there are four steps to follow to develop a PCB:

  1. Schematic circuit drawing.
  2. Relationship of the components used with your footprint. That is, correspondence between each component used and the way it will be drawn on the PCB.
  3. PCB design and routing (trail design procedure).
  4. Generation of Gerber Files (files used by PCB manufacturers to manufacture them)

It is worth mentioning that KiCad does not do circuit simulations. So, before you start designing your project's PCB, be absolutely sure that it works (do simulations, assemble your project on the protoboard beforehand and validate it).

Opening KiCad for the first time

After installing KiCad, when you open it you will see a screen with a blank project tab. Observe the following figure:

PCB design
PCB design


KiCad software opened for the first time

To start / create a new project, click File > New Project > New Project . After naming your project and choosing where it should be saved, your screen will be as shown in the image below. In blue, the .sch file stands out, corresponding to the file that will contain the schematic circuit design of your project.

Circuit board design
Circuit board design


Creating a project in the KiCad software

IMPORTANT:  Save the project to a known folder / that you have easy access to. If you save anywhere and don't care about it too much, you will have trouble backing up your project and copying the Gerber Files.

KiCad usage tips

For a better use of the tool, I leave the following tips:

  • Use it with two monitors (or a large monitor), as there will be times when it will be necessary to consult different information on different screens at the same time.
  • Have (a lot) patience. Designing a PCB from the schematic to having the gerber files is a lengthy and detailed procedure (especially for those starting out), where an error can ruin an entire batch of manufactured PCBs. Therefore, if your project requires a PCB, set aside special development time for this, preferably in environments where you will not experience many interruptions.
  • Be aware that (very) hardly a manufacturer will make a part just for you to test. There is usually a minimum batch that manufacturers impose (this varies from manufacturer to manufacturer). Therefore, review the schematic circuit and PCB several times (if possible, ask other people to review it as well) before ordering fabrication, so the loss of material (and money) is minimized.
  • How to modify a PCB after its manufacture is not so simple (and extremely not recommended), if possible, try to leave all possibilities open in the schematic circuit and in your PCB. For example, if you are going to use a microcontroller and, from it, use only a few GPIOs / pins, leave the signals from the other pins available in pin bars (or even islands).
    This is interesting because you rarely know all the directions that your project will take and, in case there is a need for expansion of functionalities, it may not be necessary to modify the PCB (= reduction in the final cost of the project).
  • Avoid using any software for PCB development in virtual machines. This software requires some processing and a good amount of RAM, making its use inappropriate in virtual machines.
  • Before actually developing a PCB, have a list of manufacturers (national and international) and, at the end of the development, make a budget with most of them. This list you can go riding with time and need for more suppliers.

Next step: schematic circuit design

You will be shown how to draw schematic circuits in KiCad and the schematic circuit design of the IoT Board Plant. Don't miss the next post!!

PCB Design or circuit board design for IoT Plant

Now, let's go ahead with the IoT Plant PCB project! Check out the first part of this series of posts , which show how to make the printed circuit board for the IoT Plant project shown here on the FILIPEFLOP blog! In this second post, I will show you how to install a library of ESP8266 components on the KiCad and how to make the schematic circuit of the PCB of the IoT Plant. Get to work!

Schematic PCB circuit

Before starting your schematic circuit design, you must have the schematic of the circuit in hand (to know what will be drawn). Therefore, below is a figure with the schematic circuit of the IoT Plant:

Circuit board design
Circuit board design


Bill of Materials

In the circuit design, the components of the list / Bill Of Materials (BOM) below will be used:

  • Two connectors with 2-terminal screws (on KiCad, they are called Screw_Terminal_1x02)
  • TO-220 encapsulation regulator 7805 (on KiCad, it is called LM7805CT)
  • NodeMCU Wifi ESP8266
  • Two 4-terminal female connector bars (on KiCad, they are called CONN_01x04) *
  • Resistor of 100Ohm 1 / 4W . In KiCad, it is simply called a Resistor.
  • 200Ohm 1 / 4W resistor . In KiCad, it is simply called a Resistor.
  • Two electrolytic capacitors (also called polarized capacitors). In KiCad, they are called Polarized Capacitor.
  • Diode 1N4007 **
  • BC337 Transistor ***

Legend:
* Although necessary to assemble the circuit and PCB, it is not necessary (it is recommended, but it is not necessary) to buy this (these) component (s).
Reason: it is possible to weld the wires on the generated islands.
** KiCad does not have this diode by default, but you can use the KiCad “generic” diode (called Diode only) to design the circuit
*** KiCad does not have this transistor by default. Therefore, you can use its equivalent, BC817 (both have the same physical dimensions and operating characteristics, so you can, when assembling the PCB, use BC337 or BC817).

Important: it   is highly recommended to place a heatsink on the voltage regulator (7805).

Creating the project and opening the schematic circuit file

First, you need to create the PlantaIoTBoard project . To do this, as shown in the topic “Opening KiCad for the first time”, create the project. After that, double click / open the project's .sch file . You should then see the schematic circuit file with nothing drawn, as shown in the following figure:

Circuit board design
Circuit board design


Screen that will contain the schematic circuit design of PlantaIoT Board

Now, everything is ready for the schematic circuit design!

ESP8266 libraries - installation

Before proceeding with the circuit design, it is necessary to install a component library from the ESP8266 line. This is necessary because, unfortunately, these components do not come by default with KiCad, but the good news is that it is quite easy to get and install them (I found a good library for ESP8266 in this GitHub repository ). To install the library, follow the procedure below.

Note: the procedures described focus on Linux, but it is easily done on Windows with similar actions.

  •  First, make a clone of the repository on your computer (in a known / easily accessible location)
    In Linux, through the terminal, execute the following commands:

?

1

two

3

4

cd ~

mkdir -p ~/kicad/libraries/

cd ~/kicad/libraries/

git clone https://github.com/jdunmire/kicad-ESP8266

  • On the schematic circuit screen, go to the Preferences > Component Libraries > Add menu and add the ESP8266.lib file (which you downloaded when you cloned the repository).
  • To add the footprints of the components: on the main KiCad screen, open the file with the name ending in “_pcb”, access the Preferences menu > Footprint Libraries Wizard and add the file  ESP8266.pretty (contained where you cloned the repository).

That done, KiCad will be ready for you to be able to design schematic and PCI circuits for the project.

Placing the circuit components in the schematic

To place a component in the schematic circuit, follow the procedure below:

  • Go to Place > Component
  • Click on the "sheet" location of the schematic circuit where you want to add a component
  • The following window will appear:
Circuit board design
Circuit board design


  • Navigate through it (or type the name of the desired component in Filter:, select the desired component and click OK.
  • Once this is done, the window will close and it will be possible to position the component on the “sheet”. To confirm the location of the component, click on it with the left mouse button.
  • If you want to rotate the component, press the Esc key, right-click on it and click Orient Component. Rotate it as desired.

Do this procedure for all components of the circuit (according to the list of components shown in this post). Your schematic circuit should look similar to the figure below:

Circuit board design
 Circuit board design


Naming the components

You may have noticed that the components are unnamed "formal" (resistors called "R?", Capacitors called "C?", Etc.). KiCad has a feature to automatically name the components of a schematic circuit. Such functionality is called Annotate schematic components . to access it, just go to Tools > Annotate Schematic .

Going to this option, a window will appear. Click on Annotate and all components are automatically named. Observe the following figure:

PCB design
 PCB design


Connecting the components

To connect the components, we will use wires . To place a wire between a terminal of one component and another element (terminal of another component, for example). follow the procedure below.

Tip: For this task, the use of zoom is recommended. To zoom in, roll the mouse scroll up and, to zoom out, roll the mouse scroll down.

  • Go to Place > Wire
  • Click on the terminal of a component you want to join to another element
  • Move the mouse to the target element to be joined by the wire (terminal of another component, for example). Click on it once.

Do this procedure until the circuit has the connections identical to the complete schematic of the PlantaIoT Board provided here (at the beginning of this post).

Using Power Ports for PCB design or circuit board design 

Power Ports are elements that represent power (+ 12V, + 5V, GND, etc.), as shown in the image below:

PCB design
PCB design


These elements are very useful as they make the schematic circuit cleaner and more understandable (especially for large circuits). To add them, follow the procedure below:

Go to Place > Power Port

Click on the "sheet" location of the schematic circuit where you want to add a Power port

The following window will appear:

PCB design for IoT


  • Navigate through the “power” options and place the + 12V, + 5V and GNDREF power ports according to the complete schematic circuit provided in the article. At the end of this process, your schematic circuit should look similar to the figure below:
PCB design MAD PCB
PCB design MAD PCB 


Schematic ready!

At this point, your schematic circuit of the IoT Board Plant is ready!

Next steps: generate the PCB and gerber files (both will be seen in part 3 of this series).

PCB Design for IoT Plant PCB Designor circuit board design 

Concluding the series of posts on the IoT Board Plant, let's see how a PCB is made and what is needed to send it for manufacturing. Check out the first and second parts of this series, which show the fundamentals and tools for PCB projects!

In summary, in this third and last post of the series, I will show how electronic components are associated with their real representations on the board (so-called footprints), how to make the PCB and, finally, what needs to be done to send the PCB to manufacture in a specialized company. Get to work!

Relating components and their actual representations

Before we go into the actual design of the PCB, an important task needs to be done: the relationship between the components of the schematic circuit and their actual representations (in more technical vocabulary, called footprints). In other words, it is necessary to inform KiCAD how we want the electronic components to be represented on the PCB.

To access this tool, we will use the shortcut on the toolbar, as shown below:

PCB Design
PCB Design 


Clicking on it, a new window will appear (depending on your computer this may take a few seconds, as this is one of the heaviest parts of KiCAD). This is the footprint association window. It is divided into three parts, with the following purposes:

  • Central part: a list of all the electronic components of your schematic circuit
  • Left part: component categories / types
  • Right part: all components of the selected category / type

Now is the time to, in addition to navigating the components, view their footprints in real time, to be more sure in the choice. For this, a footprint visualization tool will be used, accessible by a shortcut in the footprint association window itself, as shown in the following figure:

PCB Design
PCB Design


Here comes the greatest need to have a large monitor or, preferably, two monitors for this type of development. Reason? It will be necessary to navigate through the footprint association window, always keeping an eye on the corresponding footprint that appears in the footprint visualization tool. It is not impossible to do this with just one monitor, although it is a little “messy”. Using only one monitor, an image with a suggested window layout follows:

PCB Design
PCB Design


With these two tools open, select component by component in the central part of the footprint association window and choose the most suitable ones for the board. My suggestion is to use the selections seen in the central part of the footprint association window, as highlighted in black in the figure below.

PCB Design
PCB Design 


Note: it is not necessary to strictly follow this suggestion, you are free to choose the types of components you want, but keep in mind that the suggested selection aims at greater availability of the components on the market and ease of assembly / welding of the plate.

Once the association is made, just close the footprint visualization tool, close the footprint association window.

Netlist

The last step before we start, in fact, for the design and routing of the PCB is the generation of the Netlist. In summary, Netlist is a file that describes all the connections that should exist between the electronic components of your project, in addition to the relationship between the components and your chosen footprints. This is something very important, being the link between the PCB project and the schematic circuit.

To generate it, follow the procedure below:

  1. On the schematic circuit screen, on the toolbar, click on the button with a drawing with the inscription “Net”, as shown in the following figure: 
    Circuit board design
    Circuit board design

  2. A window will appear. In it, select the option "Default Format" and click "Generate". This process is also usually quite cumbersome for KiCAD, so it can take a few seconds depending on the complexity of your schematic circuit and your computer's settings
    Circuit board design
    Circuit board design

  3. Note, highlighted in the previous figure, the name of the generated Netlist file (PlantaIoTBoard.net). It can be seen from your project files on the main KiCAD screen, as shown in the figure below:
    Circuit board design
    Circuit board design

PCB: component layout

The time has come to design, in fact, the PCB! For that, we will need to run the Pcbnew tool . To do this, use the shortcut on the toolbar on the printed circuit screen, as shown in the following figure:

PCB
PCB 


Pcbnew will open. The first thing to be done on it is to load the Netlist generated in the previous topic. To do this, click on the shortcut for “Read netlist” shown in the figure below.

Circuit board design process
Circuit board design process


On the screen that appears, click "Browse", select your Netlist file and click "Read Current Netlist" and then "Close". Reading the file, as well as other things described here, may take a few seconds depending on the configuration of your computer and the complexity of your circuit.

After reading, the Pcbnew screen will be a little different, containing all the components of the la circuit, as well as the connections between them. See the figure below:

Circuit board design
Circuit board design


You may have noticed that the components are all “stacked up”. To resolve this situation and space out the components, there is a feature of KiCAD called “Global Spread and Place”. To use it, follow the procedure:

  1. Go to “View> Switch Canvas to Default”
  2. Use the shortcut illustrated in the following figure to enter to enable the “Mode Footprint”.
  3. Right-click on any empty (free of components) on the screen and access the option “Global Spread and Place”. There, click on “Spread out All Footprints”. If a dialog box appears, answer ok / yes and you are done! Your circuit should look similar to the figure below:
    Circuit board design
    Circuit board design

  4. Click on the shortcut in step 1 again to exit “Mode Footprint”

Note: although this is a very useful feature to make the circuit more visible, it will not consider the connection between them in the layout! Therefore, we still have to reposition them according to our needs and / or connections between components.

Here comes the “artistic side” of the thing: position the components so that they can be organized in a way that is easy to assemble (maybe even do with single layer, if you're lucky!). This is something that does not have much to explain, except to say that it must be done with common sense and always aiming at the best possible assembly (by "best assembly", understand the simplest, after all who will assemble / weld the sign when ready is you).

This is also the longest step: depending on your experience and “spatial view” of the circuit, it can take hours (maybe days), but don't be discouraged: it is a valuable experience for the future.
In my case, I found that the most suitable layout (aiming for a single layer board and simple to assemble) is the one shown below:

PCB design


PCB: board routing

It is time for card routing. The routing consists of connecting the components with the tracks of the printed circuit, in the desired configurations (thickness, diameter of the hole and its metallization, distance between tracks and the rest of the circuit, etc.). For beginners, printed circuit tracks are analogous to wires connecting component terminals.

There are two routing options: automatic and manual. The automatic is not recommended (especially for those who are starting in this area) because, in addition to doing a job that will need to be understood by you, it leaves a lot to be desired regarding the use of the layer (in short, it is “waste” in making trails and use layers, which means more expensive PCBs to manufacture and inefficient in space utilization). For these reasons, we will do manual routing in this article.

To do this, do the following:

  1. Select the bottom layer, as shown in the figure below.
    Note: The name B. Cu means:
    B: Background Layer
    Cu: Layer with Copper / conductive surface.
  2. That done, it means that every routing we do will be applied to the selected Layer (in this case, lower). To make a track, in the right sidebar of Pcbnew, click on “Add tracks and routes”, as shown in the figure below:
    PCB Design

  3. Choose a Pad ("circle" around the component terminal) and click once with the left button. Drag the mouse to the target pad and double-click with the left button. There, you made your first track! It will be as shown in the figure below:
    Circuit board design
    Circuit board design 

  4. Now repeat the procedure for all the tracks to be done. Here, again, it is something that requires a more “artistic” side, because you should try, at all costs, to put all the tracks on this layer. Remembering that a track can NEVER pass over another one on the same Layer!
    This is something that can take a lot of time (and patience), but you must go through this experience (it is valuable for future projects). Below is the routing that I found most convenient (and that can be done in a single layer):
Circuit board design
Circuit board design


PCB: defining the plate area and ground plane

Now, it will be necessary to define the area of ​​the plate, that is, of the entire area available for the project, select which is really relevant / should constitute your plate. In addition, the ground plan will be defined, which consists of filling all unused space by the trails with a ground conducting plan. The purpose of the ground plane is to serve as a protection against electromagnetic noises that fall / are irradiated on the plate. These noises, if impacted on the plate, will be more likely to be directed to the ground planes than to the circuit tracks, not harming the signal that travels through them. If the ground plan is not made, the noises will directly impact the trails, impairing (and, often, making unfeasible) the correct functioning of the circuit.

To define the area of ​​your plate and the land plane, do the following:

  1. In the toolbar on the right, select the option “Add filed zones”, as shown in the figure 
    Circuit board design
    Circuit board design

  2. Left-click where you want to be one of the vertices of the plate. A window will appear, asking for details of the plan that will be created. There, select the GNDREF option and click OK. See the figure below:
    Circuit board design
    Circuit board design

  3. Now, clicking with the left button to define the vertices of the plate, go through the entire plate, forming a rectangle. At the last vertex, double-click the area to be closed.
    Tip: do not make the rectangle too close to the components, this can increase the chances of PCB manufacturing errors.
  4. Click on “Perform PCB Rules Check”, as shown below
    Circuit board design
    Circuit board design

  5. A window will appear. Click on “Start DRC” and then on Ok.
    Important: this step will check your PCB for errors. If any arise, correct them immediately.
  6. Once this is done, your plate will be routed, with a defined area and with a ground plane, as shown in the figure below:
    Circuit board design
    Circuit board design

3D preview of your board

For your delight, you can have a 3D preview of your board in KiCAD! To do this, on Pcbnew, go to “View> 3D Viewer”. Notice how the board looks in 3D:

Circuit board design
Circuit board design


And to have the plate manufactured, how do I do it?

The PCB project has come to an end, but what about making the board? How is done?

For this, one of the most popular ways is to use Gerber Files. The Gerber Files are files generated by your PCB design program that show the manufacturer how each detail of the board should be done, so in possession of these files the manufacturer can manufacture the boards exactly as specified.

To generate your card's Gerber Files, follow the procedure:

  1. On Pcbnew, click on Plot, as shown below
    Circuit board design
    Circuit board design

  2. On the screen that appears, leave it as shown in the figure below
    PCB Design
    PCB Design 

  3. Click on “Browse” and define a directory where the generated files will be saved. If you prefer, create a sub-directory within your project's directory, for greater organization.
  4. Click on “Plot”
  5. Then, click on “Generate Drill File”, leave it as shown in the figure below, place the same output directory as in step 4 and click on “Drill File”.
    Okay, everything you need to have your PCB manufactured is in the directory you chose!
Circuit board design
Circuit board design


Now all you have to do is send the Gerber Files and Drill Files to the manufacturer and request a quote (and manufacturing, if the budget pleases you, of course).

 

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