4. Embedded Programming

Assignments and Assessment this week

• Group assignment:
• Demonstrate and compare the toolchains and development workflows for available embedded architectures

• Document your work to the group work page and reflect on your individual page what you learned

• Individual assignment:

• Browse through the datasheet for a microcontroller
• Write and test a program for an embedded system using a microcontroller to interact (with local input &/or output devices) and communicate (with remote wired or wireless connections)

Learning outcomes

• Implement programming protocols.

Have you answered these questions?

• Linked to the group assignment page
• Browsed and documented some information from a microcontroller’s datasheet
• Programmed a board to interact and communicate
• Described the programming process(es) you used
• Included your source code
• Included ‘hero shot(s)’

Group Assignment

—> Go to Group Assignment

Individual Assignment

Browse through the datasheet for a microcontroller

I read through several micro controllers’ data sheets.

• ESP32C3

  —> SEEED Studio ESP32C3 Explanation
  —> Purchasing Seeed Studio XIAO ESP32-C3 USD $4.90

Specification

Parameter	Description
Processor	ESP32-C3 SoC RISC-V single-core 32-bit chip processor with a four-stage pipeline that operates at up to 160 MHz
Wireless	Complete 2.4GHz Wi-Fi subsystem Bluetooth Low Energy 5.0/ Bluetooth Mesh
On-chip Memory	400KB SRAM & 4MB Flash
Interface	1x UART（Universal Asynchronous Receiver / Transmitter） 1x IIC（Inter‑Integrated Circuit） 1x SPI（Serial Peripheral Interface） 11x GPIO（General‑Purpose Input / Output）(PWM) 4x ADC (Analog to Digital Converter) 1x Reset button 1x Boot button
Dimensions	21 x 17.8mm
Power(Typ.)	Max 3.3V Output Current: 500mA Test Condition: BAT Pin Input @ 3.8V Source Capability: 3A Charging current: 380mA(Fast) / 40mA(Trickle) Input voltage (VIN): 5V Input voltage (BAT): 3.7V
Deep Sleep Power Consumption	Deep Sleep Mode: 44 μA
Wi-Fi Enabled Power Consumption	Active Mode: 75 mA Modem-sleep Mode: 25 mA Light-sleep Mode: 4 mA
BLE Enabled Power Consumption	Modem-sleep Mode: 27 mA Light-sleep Mode: 10 mA
Working Temperature	-40°C ~ 85°C

Pin Map

Pin List

XIAO Pin	Function	Chip Pin	Alternate Functions	Description
5V	VBUS		Power Input/Output
GND
3V3	3V3_OUT			Power Output
D0	Analog	GPIO2	ADC1_CH2,	GPIO, ADC
D1	Analog	GPIO3	ADC1_CH3	GPIO, ADC
D2	Analog	GPIO4	ADC1_CH4, FSPIHD, MTMS	GPIO, ADC
D3	Analog	GPIO5	ADC2_CH0, FSPIWP, MTDI	GPIO, ADC
D4	SDA（Serial Data Line）	GPIO6	FSPICLK, MTCK	GPIO, I2C Data
D5	SCL（Serial Clock Line）	GPIO7	FSPID, MTDO	GPIO, I2C Clock
D6	TX（Transmit）	GPIO21	U0TXD	GPIO, UART Transmit
D7	RX（Receive）	GPIO20	U0RXD	GPIO, UART Receive
D8	SCK（Serial Clock）	GPIO8		GPIO, SPI Clock
D9	MISO (Master In, Slave Out)	GPIO9		GPIO, SPI Data
D10	MOSI (Master Out, Slave In)	GPIO10	FSPICS0	GPIO, SPI Data
MTDO		GPIO7		JTAG (Joint Test Action Group)
MTDI		GPIO5		JTAG, ADC
MTCK		GPIO6		JTAG, ADC
MTMS		GPIO4		JTAG, ADC
Reset		CHIP_EN		EN (Enable)
Boot		GPIO9		Enter Boot Mode
U.FL-R-SMT1		LNA_IN		UFL antenna (for Wi‑Fi / Bluetooth / GPS)
Light		VCC_3V3		CHG-LED

• ESP32 Datasheet

• Nomenclature
  

• Pin Layout
  

* Pin Overview

• SEEED XIAO RP2040

XIAO RP2040 Pin Map

Firstly, I wanted to make a system by pushing a button to light the LED and send a message to PC that lighting condition either light on or light off.

• RP2040 Datasheet

Plug in XIAO RP2040 USB-C to PC USB-C port by pressing the Board’s reset button locates at the bottom left.

Connect the board to PC via USB-C.

If the PC could consider the USB-C input as the external board, you will see the following;

RP2040 being designed for “Rasberry Pi”, the setup of Adruino IDE should be chosen as “Rasberry Pi”.

As a beginner, I asked Copilot the following question to see how the normal programming would be.

I am using XIAO RP2040.
connect from XIAO RP2040 D0 to a Button Switch 
Button Switch to ??? which pin should I input?
GRD pin to resister 
resister to LED light - 
LED light + to ??? which pin should I input?

I had following answer from copilot;
| Purpose | Pin | |---------|--------| |Button input|D0| |LED output|D1| |Ground|GND| |Power|Not needed (we use internal pull‑up)|

We will: * Use INPUT_PULLUP for the button (no resistor needed for the button) * Use one resistor (220–330Ω) for the LED

2️⃣ Wiring (important part) ✅ Button wiring (D0) You asked:

Button Switch to ??? which pin should I input?

Correct wiring: D0 ─── Button ─── GND

One side of the button → D0 Other side of the button → GND No resistor needed (we use internal pull‑up)

Logic:

Button NOT pressed → D0 = HIGH Button pressed → D0 = LOW

✅ LED wiring (D1) You asked:

GND pin to resistor to LED light – LED light + to ??? which pin should I input?

Correct wiring: D1 ─── Resistor (220–330Ω) ─── LED + (long leg) LED – (short leg) ─── GND

So:

D1 → resistor → LED + LED − → GND

⚠️ LED polarity matters:

Long leg = + Short leg = −

✅ Summary wiring diagram (text) XIAO RP2040

D0 ── Button ── GND

D1 ── 220Ω ── LED(+) LED(-) ── GND

3️⃣ Arduino program (Button toggles LED + sends message) This program:

Press button → LED toggles ON / OFF Sends message to PC:

“LED is ON” “LED is OFF”

Complete code by Copilot

const int buttonPin = D0;
const int ledPin = D1;

bool ledState = false;
bool lastButtonState = HIGH;

void setup() {
  pinMode(buttonPin, INPUT_PULLUP); // internal pull-up
  pinMode(ledPin, OUTPUT);

  Serial.begin(115200);
}

void loop() {
  bool buttonState = digitalRead(buttonPin);

  // Detect button press (HIGH → LOW)
  if (lastButtonState == HIGH && buttonState == LOW) {
    ledState = !ledState;              // toggle LED
    digitalWrite(ledPin, ledState);

    if (ledState) {
      Serial.println("LED is ON");
    } else {
      Serial.println("LED is OFF");
    }

    delay(200); // simple debounce
  }

  lastButtonState = buttonState;
}

4️⃣ What you will see 🔹 On the board

Press button → LED turns ON Press again → LED turns OFF

🔹 On PC (Serial Monitor, 115200 baud) LED is ON LED is OFF LED is ON

5️⃣ Common mistakes to avoid ❌ Connecting LED without resistor ❌ Connecting button to 3.3V instead of GND when using INPUT_PULLUP ❌ Forgetting LED polarity ❌ Using D0 for Serial RX (XIAO RP2040 is OK, unlike Arduino Uno)

In order to understand the meaning of each command, I also asked Copilot as follows;

Can you explain the meaning of each coding line of following coding line by line?

I made explanation sheet based on the explanation from Copilot as follows;

Firstly, I copied above code into my Arduino IDE as follows;

Although the board works as requested, there is an error at the bottom end of the Arduino IDE telling “Not Connected. Select a board and a port to connect automatically.”

Then I asked the copilot again as follows;

Serial monitor is telling not connected to the board

Copilot: That message is normal Arduino IDE 2 behavior and it means Arduino IDE does not currently know which board + port to connect the Serial Monitor to. We’ll fix it step by step. This is not a wiring problem.

✅ What the message means

“Not connected. Select a board and a port to connect automatically.”

This means one (or both) of these is missing:

❌ Board not selected ❌ Port not selected

Serial Monitor cannot connect until BOTH are selected.

✅ Step‑by‑step fix (do this in order) ✅ 1. Close Serial Monitor First, close the Serial Monitor tab.

✅ 2. Select the Board (very important) In Arduino IDE menu: Tools → Board → Seeed RP2040 Boards → Seeed XIAO RP2040

✅ After this, the board name should appear at the top bar of Arduino IDE.

✅ 3. Select the Port (this fixes 90% of cases) Now go to: Tools → Port

You should see one new port after plugging in the board. Choose:

Windows → COMx macOS → /dev/tty.usbmodemXXXX Linux → /dev/ttyACM0

✅ If no port appears, see section ⚠️ If NO port appears below.

✅ 4. Upload the sketch again Click Upload (→) and wait for: Done uploading.

✅ This confirms the board + port are correct.

✅ 5. Open Serial Monitor again Tools → Serial Monitor

Now the yellow bar should be gone ✅

✅ 6. Set Baud Rate Bottom‑right of Serial Monitor: 115200

Must match: C++Serial.begin(115200);その他の行を表示する

✅ Expected result Now when you press the button, you should see: LED is ON LED is OFF

Following the guidance of Copilot, I selected Port as follows;

Serial Monitor Selected;

Then, the Serial Monitor responded as follows;

Press button circuit with XIAO RP2040

Here under is the video of “Push Button LED”.

I need to understand why it sometimes changes the behavior by “continuous pushing” and “one quick pushing”.

Files

• Arduino: LED Blinking

• Arduino: Push Button LED