7. Electronics design¶

This week I worked on designing and build Print Circuit Board(PCB). One of dreams project is to build my own Arduino Board. To start I build an Arduino UNO board.

Group assignment:

Use the test equipment in your lab to observe the operation of a microcontroller circuit board (in minimum, check operating voltage on the board with multimeter or voltmeter and use oscilloscope to check noise of operating voltage and interpret a data signal)
Document your work (in a group or individually)

For the Group Work please check the Group Page for more details.

Individual assignment:

Redraw one of the echo hello-world boards or something equivalent, add (at least) a button and LED (with current-limiting resistor) or equivalent input and output, check the design rules, make it, test it.

Tools I have used for this Project - EasyEDA

PCB Design¶

For PCB design I used EasyEDA which is an Easy and powerful online PCB Design tool.

Before start designing the PCB board check the Fab Lab Electronics inventory and select the components for this project. Datasheets can be found in https://www.digikey.com

Ohm’s law
Ohm’s law is a relationship between the voltage, current, and resistance in any circuits.

www.mstworkbooks.co.za

LED Circuit

To find the right resistor for the LED check the LED Datasheet

VCC = 5V
LED Forward Voltage = 1.8V
LED Forward Current = 20 mA
R Voltage = VCC - LED Voltage = 3.3V - 1.8V = 3.2V

Now use Ohm’s law as following:

R = V/I = 3.2/0.02 = 160 Ω

Microcontroller The microcontroller for Arduino UNO is ATMEGA328P which is a low power 8-bit microcontroller.

After reading the Datasheet here are some of the features:-

PWM Channels: 6
Program Memory Size: 32KB
CPU Speed: 20 MIPS Throughput at 20MHz
ADC Channels: 8
Operating Voltage: 1.8 - 5.5
Pin Count: 32
SPI: 2
Temperature Range: -40 - 85°C

Components:

Here the list of components I have used for this project

ID	Name	Designator	Qty.	Datasheets
1	SMD_HEADER_1X8	1	1
2	22pF	C1,C2	2
3	10uF	C4,C5	2
4	0.1u	C6	1
5	210SMT-2*3P Gold-plated black	H1	1
6	FTDI-SMD-HEADER	H2	1
7	SMD_HEADER_1X6	H4,H5	2
8	LTST-C150CKT	LED1,LED2	2	Datasheet
9	10K	R1	1
10	1k	R2,R3	2
11	ATMEGA328P-AU	U1	1	Datasheet
12	ZLDO1117G50TA	U3	1
13	16MHz	X1	1

Schematic Diagram Start designing the PCB with the schematic diagram and place all the components you need the sketch.

As I’m making my own Arduino Uno design I have checked the official schematic design arduino-uno-smd-schematic.pdf and Arduino pinout for ATMEGA328P-AU

forum.arduino.cc

Start with the basic requirements for the ATMEGA328P-AU setup
Create the Schematic for power module
Create the schematic for the ISP port
Create the schematic for the FTDI Port
Create the schematic for IO Ports
Check the schematic Diagram

PCB

After finishing from schematic diagram design now time to design the PCB

In EasyEDA go to File ==> New ==> PCB to create PCB project
Then go Design ==> Import Changes to get all the Components and wire connections from the schematic diagram.

Now move the components to their places and create the traces and try to NOT make 90 degree angle for the PCB track.

Set the Design Rule for the PCB Make the Track clearance “0.381mm” which is the minimum path for needed for the milling bit (1/64)
Go to Design ==> Check ERC and make sure you don’t have any error
Export the TopLayer of the PCB design to SVG
Repeat the same step for the Outline
Upload the files to fab modules and create the G-code. For more details please follow the instruction in Electronics production

Problem - Not able to get all traces for the ATMEGA328P-AU in fab modules, because of the pads size is 0.4mm

Solution - Change the Pad width size from 0.4mm to 0.35mm and repeat the the above steps again.

Now I got nice traces lines in fab modules

PCB Production¶

For PCB production I have used the Desktop Milling Machine Roland SRM-20 and follow the instruction in Electronics production

Problem: After follow the instruction in Electronics production and finished the cut I found that some cobber stuck to milling bit and destroy all the small traces for ATMEGA
Solution: Check the milling bit with microscope before start cutting
Now I got nice and clean PCB Board