Week 15 - Networking and Communcations


Networking and Communications

Networks have become ubiquitous. Internet communication enabled by Wifi technology, Bluetooth, new kids on the block like LoRa are everywhere. Still, a lot of wired communication like Serial, SPI, I2C are still an integral part of connected devices. In my final project, I will probably use the serial communication to connect my modified Satshakit to a Raspberry Pi Zero W. Therefore, I will build a second board (ComBoard) to experiment with the serial communication.

So here is the assignment for Week 15:

Making the ComBoard

I modified my HelloBoard from week 06, this time routing all the remaining ports including the serial communication.

Designing the board

All ports added.

image Schematic_ComBoard Modified HelloBoard schematic
image Layout_ComBoard Modified HelloBoard schematic
image Layout_ComBoard Modified HelloBoard schematic

Milling the PCB

Ahh, same mistake as earlier, too low isolation! Luckily, I saw this in FabModules. I went back to Eagle and increased it setting 0.02.

image LowIsolation Too low isolation setting
image BetterIsolation Isolation of 0.02 gives a good result.
Here are the internal and external files for engraving and cutting.
image ComBoard_Internal Internal engraving
image ComBoard_External External cut
image ExternalCutSettings External cut settings

The result came out just fine.

image EngravingResult Internal result
image CuttingResult Cutting result


After updating with Ratnest, I realized that some traces were lost by increasing the isolation. This only affects the ground layer, so will solve the problem with wires and a few more zero ohm resistor.

Bill of materials

image SolderingPlan Soldering schematics
image SolderingComplete Quick fix using wire and zero ohm resistors


Once the soldering was completed. I started to programm the ComBoard. I used an Arduino Uno as an ISP programmer, burned the bootloader and followed up with programming via SPI. A simple blink sketch proved that the ComBoard was working.

image WiringBurnBootloader SPI connections - similar board
image CuttingResult Blink working

On the ComBoard, we will use PA0 as RX and PA1 as TX which are 0 and 1 in the Arduino IDE.

image SerialPorts Pin layout ATtiny 44

The ComBoard does not have hardware serial communication, so I will use the software serial.

// Joern Kiwitt - Serial Communication test //

#include < SoftwareSerial.h>

// MySerial object(Rx, Tx)
SoftwareSerial mySerial(0,1);

void setup() {

void loop() {
  mySerial.print("hello Satshakit, this is ComBoard");

For the software serial on the Satshakit, I will use PD2 (Arduino pin 2) as RX_SoftwareSerial and PD3 (Arduino pin 3) as TX_SoftwareSerial. This can be varified, checking the documentation from week 10.

image SerialPorts Serial ports for the connection to the ComBoard
image SerialConnected Serial RX & TX as well as GND

I will use Serial.write to write characters to the serial.

// Joern Kiwitt - Serial Communication test //

#include < SoftwareSerial.h>

const char* message;

// MySerial object(Rx, Tx)
SoftwareSerial mySerial(2,3);

void setup() {

void loop() {
  Serial.println("hello ComBoard, this is Satshakit");
  bool avabl=false;

  while (mySerial.available() > 0) {   

if (!avabl){
  Serial.println("not available");

To connect the serial ports, remember to also share the GND. After doing so, the ComBoard serial, send via software serial to the Satshakit can be read from the serial monitor of the Satshakit.

image CommunicationWorking It works: receiving data from the ComBoard

As the speed of the two microprocessors is slightly different, sometimes the message won't go through completely, but in general the message goes through.

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