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To design printed circuit boards, there are many tools to choose from, such as open source software "KiCAD" or various online services. The most beloved software in the open source hardware community is "EAGLE" by CadSoft.
In this article, you will learn how to use EAGLE this software to do basic printed circuit board design and make the basic core of ATmega microcontroller board.
Parts List
▪ Resistance, 10K 1/8W
▪ Electrolytic capacitor, 47μf (2)
▪ Resistance, 1K 1/8W
▪ Momentary button switch
▪ Ceramic resistor, 16MHz
▪ ATmega328P microcontroller IC, ATmega 328P
▪ IC socket, 28 pins (not necessary)
▪ Diode, 4005
▪ Low-Dropout Linear Regulator (LDO), L4931
▪ Power socket
▪ 1*6 pin header
▪ Ceramic capacitor, 0.1μf (2)
Tool list
▪ A Windows, Mac or Linux computer that can connect to the Internet
▪ Cadsoft EAGLE stand-alone PCB design software
▪ RBBB EAGLE parts database
Note: RBBB's parts list is shown above, but you don't really need to have parts in hand, you can follow the design instruction below.
Use EAGLE
EAGLE is a software package that integrates multiple programs, and each function has a corresponding design process. This time we will focus on "Schematic Editor" and "Board Editor"; other modules include Autorouter and Component Editor, CAM processing software (CAM Processor, used to create files for machining) and an interface for programming user language programs (User Language Programs).
We can select the components to be used from the component library, and each component will have two types of icons, which are used for the circuit schematic and the circuit board respectively. Since most of the components come from different component libraries (packages), and EAGLE’s component library allows different packages to link the same component icon, in order to simplify the process, we have made an RBBB containing the components required for this design. Database, after you are familiar with the design process, another SparkFun database will be a good springboard to broaden your horizons.
Work flow designed by EAGLE
I. Design and search for materials: find parts, read specifications, download what you need, and draw blueprints.
II. Circuit schematic design: connect various components with signal wires.
III. Circuit Rule Check (ErC): Use artificial intelligence (AI helper) to check errors on the circuit.
IV. Circuit board design: Put the design components on the circuit board and design real circuits to connect them.
V. Design Rule Check (DrC): Use artificial intelligence to check design errors.
Create Gerber files and drill files: Use CAM processing software to create files for machining.
1. Start making
First, please download EAGLE Light Edition from the Cadsoftusa.com website, and download the RBBB component database from moderndevice.com/downloads, and put the package into the lbr database in the EAGLE program database.
EAGLE uses colors to distinguish layers with different functions in CAD drawings. In the "Circuit Schematic Editing" window, the component icon is in the "Symbols layer", and its label will be in the "Names layer" or "Values layer", And the network connection (Net) is in the "Net layer", you can show or hide these layers through the View Menu.
Tip: Please check your toolbar from time to time to confirm whether it is drawn on the right layer.
1.1 Open the schematic editor and select "File" - "New" - "Schematic". You will get a warning message "No forward/backward annotation will be performed.", because under normal circumstances you will open the schematic diagram and the board editor at the same time. They are synchronized, so this message just tells you that the PCB file has not been opened yet.
Open the schematic editor and select "File" - "New" - "Schematic".
1.2 Select the "Add" tool and place the Frame component in the RBBB component database on the construction paper. This is not necessary, but this step is very simple and allows you to draw the circuit schematic diagram without constant adjustments. The size of the screen.
2. Power circuit
These 5 components are responsible for receiving DC power input and outputting a 5V power supply without noise.
The icon in the center is a voltage regulator. The most important specifications of the voltage regulator are output voltage, maximum output current and dropout voltage, the smallest difference between input and output potential. ). The minimum voltage difference of the L4931 voltage regulator is only 0.4V, so it is very reliable to output 5V from the 6V input terminal (from 4 AA batteries). Its supply current can be as high as 250mA, which is very sufficient for most microcontroller applications.
Rule of thumb
▪ A small dot indicates that the two intersecting signal lines are connected; no small dot indicates that they are just overlapping.
▪ Use the Grid tool and set its size to 0.1inch (100 mil), because the most common mistake is that two lines seem to intersect but are not connected.
▪ Each line (network connection or signal line) has an independent name. Even if they are not adjacent on the screen, all signal lines with the same name will be automatically connected together. This function is very convenient. If you have a lot of components that need to be connected by connection, the screen must be a mess.
▪ Each component should have an obvious name and value. You will need to move the labels to make them clear and legible; use the Smash tool to separate the labels from the components, and move or rotate them to their proper values. Location.
▪ Drawing a schematic circuit diagram is like using circuit components to communicate with others. Think about whether you have provided all the functions they need.
2.1. Use the "Add (Add)" tool, select RBBB - Regulator, place the Regulator component on the quadrant in the upper left corner of the screen, and use the new tool to configure two Electrolytic_Caps components, GND components and +5V signal supply components (RBBB - Supply)
2.2. Use the "Net" tool to connect the output and input of the voltage regulator to the positive poles of the two capacitors, then connect the negative pole of the capacitor to the ground wire of the voltage regulator, and connect the ground wire to the PCB GND component, and connect the output terminal of the voltage regulator to the +5V signal supply component.
2.3. Use the Value tool to set both capacitors to 47μF.
2.3. Use the Value tool to set both capacitors to 47μF.
2.4. Add RBBB-Power_Jack and place it next to the input terminal of the voltage regulator. This is a very standard center-positive power socket (if you don’t consider the electronic equipment for music), connect its center pin to the input end of the voltage regulator and connect the sleeve end to ground. If the "Connect Net Segments?" dialog box pops up, please select "Yes".
Add RBBB-Power_Jack and place it next to the input terminal of the voltage regulator.
2.5. Add a new diode, it will appear on the screen in a horizontal state, please use the "Rotate" tool to turn its negative side up, and use the "Network Connection" tool to connect it to the voltage Between the input terminal of the regulator and the ground terminal.
2.5. Add a new diode, it will appear on the screen in a horizontal state, please use the "Rotate" tool to turn its negative side up, and use the "Network Connection" tool to connect it to the voltage Between the input terminal of the regulator and the ground terminal.
2.6. Finally, select the 1*2 header (RBBB-1x2_Pinhead) as an additional selective power input, rotate and place it, connect one of the pins to the power supply and the other to the ground.
