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,, PCB: Printed Circuit Board ), so you can go out into the field without fear (and, in addition, give your project a more professional look).

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.

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:

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.

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:

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:

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:

?

• 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:

• 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:

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:

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 Pla