🙋 Individual Assignment

Task: Measure something — Add a sensor to a microcontroller board that you have designed and read it.

Goals:

• Design and build a custom microcontroller board with input capability.
• Integrate an analog or digital sensor.
• Write firmware to read and process sensor data.

Steps:

• Choose a sensor: I chose an RFID sensor controlled by the XIAO RP2040 Module
• Microcontroller:Seeed XIAO RP2040 module
• Sensor:RFID-RC522 for reading RFID tags
• Power:Supplied via USB-C to the XIAO RP2040, which provides 3.3V to the RFID-RC522
• Headers:GPIO breakout (J4 and others) for SPI and control pins
• Programming Interface:USB-C on the XIAO RP2040 for bootloader and programming
• Design/update: XIAO RP2040:Powered via USB-C, provides 3.3V and GND to the RFID-RC522.
• RFID-RC522:
• VCC: Connected to 3.3V on XIAO RP2040 (red cable)
• GND: Connected to GND on J4 header (black cable)
• RST: Connected to D0 (GP0) on XIAO RP2040 (white cable)
• SDA (SS): Connected to D1 (GP1) on XIAO RP2040 (orange cable)
• MISO: Connected to D9 (GP4, SPI0 MISO) on XIAO RP2040 (grey cable)
• MOSI: Connected to D10 (GP7, SPI0 MOSI) on XIAO RP2040 (purple cable)
• SCK: Connected to D8 (GP6, SPI0 SCK) on XIAO RP2040 (brown cable)
• Headers: J4 and other headers provide access to GPIO and SPI pins, as seen in the PCB layout screenshot.




• PCB Layout


• Board Size:71mm x 55mm, 1-layer

• Assemble and test the board:



• The board is assembled with the XIAO RP2040 soldered and RFID-RC522 connected via jumper wires, as shown in the user’s photo. Testing confirms successful RFID tag reading via the serial monitor at 115200 baud.




• Write Arduino IDE code to


• Initialize the sensor
• Read and display sensor data
• Debug and calibrate if necessary.

            #include <SPI.h>
              #include <MFRC522.h>
              
              #define SS_PIN D1  // SDA pin, connected to D1 (GP1) via orange cable
              #define RST_PIN D0 // RST pin, connected to D0 (GP0) via white cable
              
              MFRC522 rfid(SS_PIN, RST_PIN);
              
              byte nuidPICC[4];
              
              void setup() { 
                Serial.begin(9600);
                while (!Serial);
                SPI.begin(); // SPI pins: SCK (D8, GP6, brown), MISO (D9, GP4, grey), MOSI (D10, GP7, purple)
                rfid.PCD_Init();
                
                if (rfid.PCD_PerformSelfTest()) {
                  Serial.println(F("RC522 initialized successfully."));
                } else {
                  Serial.println(F("RC522 initialization failed! Check connections."));
                  while (1);
                }
              
                rfid.PCD_SetAntennaGain(rfid.RxGain_max); // Maximize read range
                Serial.println(F("This code scans the MIFARE Classic NUID."));
              }
              
              void loop() {
                if (!rfid.PICC_IsNewCardPresent()) return;
                if (!rfid.PICC_ReadCardSerial()) return;
              
                Serial.print(F("PICC type: "));
                MFRC522::PICC_Type piccType = rfid.PICC_GetType(rfid.uid.sak);
                Serial.println(rfid.PICC_GetTypeName(piccType));
              
                if (piccType != MFRC522::PICC_TYPE_MIFARE_MINI &&  
                    piccType != MFRC522::PICC_TYPE_MIFARE_1K &&
                    piccType != MFRC522::PICC_TYPE_MIFARE_4K) {
                  Serial.println(F("Your tag is not of type MIFARE Classic."));
                  return;
                }
              
                if (rfid.uid.uidByte[0] != nuidPICC[0] || 
                    rfid.uid.uidByte[1] != nuidPICC[1] || 
                    rfid.uid.uidByte[2] != nuidPICC[2] || 
                    rfid.uid.uidByte[3] != nuidPICC[3]) {
                  Serial.println(F("A new card has been detected."));
                  for (byte i = 0; i < 4; i++) {
                    nuidPICC[i] = rfid.uid.uidByte[i];
                  }
                  Serial.println(F("The NUID tag is:"));
                  Serial.print(F("In hex: "));
                  printHex(rfid.uid.uidByte, rfid.uid.size);
                  Serial.println();
                  Serial.print(F("In dec: "));
                  printDec(rfid.uid.uidByte, rfid.uid.size);
                  Serial.println();
                } else {
                  Serial.println(F("Card read previously."));
                }
              
                rfid.PICC_HaltA();
                rfid.PCD_StopCrypto1();
                delay(1000); // Prevent serial flooding
              }
              
              void printHex(byte *buffer, byte bufferSize) {
                for (byte i = 0; i < bufferSize; i++) {
                  Serial.print(buffer[i] < 0x10 ? " 0" : " ");
                  Serial.print(buffer[i], HEX);
                }
              }
              
              void printDec(byte *buffer, byte bufferSize) {
                for (byte i = 0; i < bufferSize; i++) {
                  Serial.print(' ');
                  Serial.print(buffer[i], DEC);
                }
              }
          

Personal reflection: challenges, learnings, improvements



• I struglled to make the RFID-RC522 to work on receiving the signals from the cards. Though I am still lerning on how to program microcontrollers I am learning fast by the use of AI tools such and Grok and ChatGPT. I have again learnt that even if they help with coding from the connections they are alwys wrong and I have to do a though check and this took a long time because the code wasnt working.. I got assistance from my collegues and we got the code right. The other this that came up was the issue of the usb cable not working. The Tag will scan then stop and until I changed cables thats when everything started working properly. It was tough but a good learning experience. The translation from Botswana Lanuage is that the tag is refusing to work.



Deliverables:

• KiCAD/Schematic and PCB layout files
• Photos of the board and sensor
• Commented code
• Screenshot/log of sensor readings
• Personal reflection: challenges, learnings, improvements

🛠️ Tools & Skills

• Multimeter, oscilloscope, serial plotter
• Microcontroller programming (C/C++ or Python)
• KiCAD/Eagle for PCB design
• Soldering and debugging