Week 3 – Embedded Programming
Assignment Brief
Program a microcontroller to interact with input and/or output devices, experimenting with different development environments.
Project: Kaio-ken Animation System
Built an interactive OLED display system with capacitive touch input, featuring animated graphics inspired by Dragon Ball's power-up effects. A deliberate side project to explore embedded programming fundamentals while traveling for work—no forced connection to the final project this week.
Hardware
- Microcontroller: Seeed Studio XIAO RP2040 (RP2040 dual-core ARM Cortex-M0+ @ 133MHz)
- Display: 0.96" OLED (128×64, SSD1306 driver, I2C)
- Input: Two capacitive touch pads (GPIO 2 & 3)
- Output: Optional piezo buzzer (GPIO 6) or built-in LED
- PCB: Custom milled carrier board with breakout headers
Demo Video
Software Features
Capacitive Touch Sensing
Implemented resistor-less capacitive touch using GPIO discharge timing:
- Pad 0 (GPIO 2): Toggle animation on/off
- Pad 1 (GPIO 3): Cycle power level (1-5)
- Dynamic baseline calibration on startup
- Hysteresis for reliable touch detection (120μs threshold, 40μs release)
OLED Animation
- 25 FPS animated "aura" effect using concentric circles
- Sine-wave modulation for pulsing radius
- Animation speed scales with power level (1.5-4.0 rad/sec)
- Real-time state display (ON/OFF, Level 1-5)
Audio Feedback
- Non-blocking beep queue (6 events)
- Rising triad on activation (700Hz → 1000Hz → 1300Hz)
- Short tick on level change (850Hz, 50ms)
- Heartbeat LED pulse when active (period decreases with level)
Key Code Sections
Capacitive Touch Measurement
unsigned long measureCapacitanceTick(uint8_t pin) {
pinMode(pin, OUTPUT);
digitalWrite(pin, HIGH);
delayMicroseconds(10); // Charge
pinMode(pin, INPUT); // High-impedance
unsigned long start = micros();
while (digitalRead(pin) == HIGH) {
if ((micros() - start) > 3000) break; // Timeout
}
return micros() - start; // Discharge time
}Animation Rendering
void drawAura(int cx, int cy, float phase, uint8_t level) {
int baseR = 12 + (level-1)*3; // Radius grows with level
for (int r=0; r<3; r++) {
int rr = baseR + r*2 + (int)(sin(phase*2.0)*2); // Pulse
display.drawCircle(cx, cy, rr, SSD1306_WHITE);
}
}Technical Learnings
- Capacitive sensing without hardware: GPIO discharge timing works surprisingly well. Touch detection is reliable with proper baseline calibration.
- Frame timing matters: Fixed 40ms frame time (25 FPS) prevents animation speed from varying with code complexity.
- I2C display optimization: SSD1306 uses a RAM framebuffer—only call
display.display()once per frame to avoid flicker. - Non-blocking audio: Beep queue allows sound effects without
delay()blocking animation. - Power considerations: OLED active pixels draw significant current—full white screen pulls ~20mA, black pixels ~8mA. Animation keeps average current around 12mA.
Challenges Solved
Touch pad false triggers: Initial touch detection was noisy. Solution: Added 40μs release hysteresis (separate thresholds for press/release) and averaged 5 samples during baseline calibration.
Screen tearing: Animation had visible horizontal tears. Solution: Moved display.clearDisplay() to start of frame, drew all graphics, then called display.display() once at end.
Why No Connection to Orbis?
This week I was traveling for work and wanted to keep the assignment focused on core embedded programming concepts rather than forcing a thematic link to the final project. Sometimes it's valuable to explore tangential ideas—capacitive sensing and display animation are useful skills, even if they don't directly map to Orbis.
That said, the I2C display code is directly reusable for Orbis's OLED, and understanding non-blocking timing will be critical for managing rotary encoder interrupts alongside display updates.