week 10

Output Devices

Power Consumption & Actuator Integration

Measuring DC motor power at different duty cycles
Integrating OLED displays, servo motors, and pneumatic actuators

Individual Contributions

👩
Micaela Córdova — OLED Display Integration

Role in Group: Data collection and circuit setup. Measured voltage using multimeter connected in parallel across motor.

Individual Focus: Integrated a 0.96" OLED SSD1306 display into her custom Week 8 PCB using I2C (only 2 wires needed). Created 6 rotating screens every 5 seconds displaying cycle status, stock levels, and motivational messages for her final HigiBox project.

  • XIAO nRF52840 with native I2C support (D4 SDA, D5 SCL)
  • Non-blocking timing using millis() for 5-second screen rotation
  • Adafruit GFX library for graphics rendering
👨
André Mamani — Motor Control & Actuator Testing

Role in Group: Hardware assembly, motor control via PWM signals, L298N driver setup, and current measurements with multimeter in series.

Individual Focus: Tested multiple output actuators — servo motor for precision angular control (0°, 90°, 180°) and air pump for pneumatic soft motion. Selected air pump for final project based on design philosophy. Documented power amplifier requirements for motors.

  • Servo motor control with 3-position cycling and LED feedback
  • L298N H-bridge motor driver for power amplification
  • Pneumatic air pump actuation with directional control
✅ Week 10 Goals (All Completed)
✓ Measure Power Consumption

DC motor tested at 5 duty cycles (50%–100%). Measured voltage, current, and calculated power (P = V × I).

✓ Integrate Output Devices

OLED display (Micaela) and servo/air pump actuators (Andres) successfully connected and operating on microcontroller boards.

✓ Document & Demonstrate

Video demonstrations, power data table, hardware photos, and lessons learned for all output devices.

Section 1: Power Consumption Fundamentals

Theory & Measurement Methodology

⚡ The Power Formula

P = V × I

Power (Watts) = Voltage (Volts) × Current (Amperes). Understanding power consumption is critical for component selection, efficiency optimization, and safe circuit operation.

P = V × I

Direct method: Voltage × Current. Use when you can measure both simultaneously with multimeters.

P = I² × R

When current & resistance known. Current squared multiplied by resistance.

P = V² ÷ R

When voltage & resistance known. Voltage squared divided by resistance.

📏 Measurement Setup: Series vs Parallel
Current: Series Connection

Ammeter connected in series with load. The multimeter becomes part of the current path with minimal resistance (~0 Ω). All current passes through it.

Voltage: Parallel Connection

Voltmeter connected in parallel with load. The multimeter has very high resistance (~∞ Ω). Draws virtually no current, doesn't disturb circuit.

Key Insight: In our group test, we used two multimeters simultaneously — one in series for current, one in parallel for voltage. This gave us V and I at the same moment, allowing direct P = V × I calculation.
🔧 System Components (Group Test)
Component Spec Role
DC TT Motor 6V, 200 RPM (dual-shaft geared) Load being measured. Standard robotics motor.
DRV8833 Driver Dual H-bridge, 1.2A per channel max Controls motor direction and speed via PWM from microcontroller.
18650 Lithium Battery 3.7V nominal (worn during testing) External power for motor circuit. Showed weakness at low duty cycles.
Multimeters (×2) Standard digital multimeters One measuring current (series), one measuring voltage (parallel).
💡 Key Discovery: Motor Power is Load-Dependent

Unlike fixed resistors, motors don't consume constant power. Motor power varies based on:

  • Speed (duty cycle): Higher duty = higher speed = higher current draw
  • Mechanical load: Friction, resistance, or external force increases current demand
  • Temperature: Warm motor has higher resistance than cold motor (minor effect)

The motor demands power proportional to load. The driver supplies what's needed (up to 1.2A max). Understanding this prevents silent failures where motors stall without warning.

Section 2: Group Assignment Results

Measuring DC Motor Power Across Duty Cycles

📊 Power Measurements (5 Duty Cycles)
1
50% Duty — Insufficient (Battery too weak)

Current: 0.042 A | Voltage: — | Power: —

Battery voltage dropped below motor threshold. Motor wouldn't spin. Highlighted aging battery limitation.

2
65% Duty ★ Minimum Threshold

Current: 0.084 A | Voltage: 1.389 V | Power: 0.1167 W

Just enough voltage to overcome motor static friction. Motor begins rotating. First viable operating point.

3
75% Duty — Medium Speed

Current: 0.120 A | Voltage: 1.38 V | Power: 0.1656 W

Stable operation. Motor rotating smoothly at moderate speed. Good balance between power and safety.

4
~82.5% Duty — High Speed

Current: 0.122 A | Voltage: 4.2 V | Power: 0.5124 W

Voltage jumped as battery recovered charge. Motor running at higher speed with noticeably stronger performance.

5
100% Duty ★ Maximum Power

Current: 0.150 A | Voltage: 7.15 V | Power: 1.0725 W

Full power. Motor at maximum speed with highest torque. Demonstrates full capability of system.

📋 Comparative Data Table
Duty Cycle Current (A) Voltage (V) Power (W) Status
50% 0.042 — — ✗ Insufficient
65% ★ 0.084 1.389 0.117 Minimum threshold
75% 0.120 1.38 0.166 Stable
82.5% 0.122 4.2 0.512 High speed
100% ★ 0.150 7.15 1.073 Maximum power
🎯 Key Observations
Power Scales Dramatically with Duty

65% → 100% shows 9× increase in power (0.117 W → 1.073 W). Not linear — motor efficiency varies across speed range.

Load Always Increases Current

When we applied mechanical load (hand pressure), current immediately increased. Motor pulls more current to maintain rotation against resistance.

Battery State Matters

Worn 18650 caused 50% and 65% failures. Fresh battery would likely work. Component aging degrades system behavior.

Driver Supplies On-Demand

DRV8833 doesn't force current into motor. It supplies whatever current motor demands, up to 1.2A limit. Motor is the "customer" — driver fulfills its requests.

Section 3: Individual Output Devices

Display Integration & Actuator Testing

👩 Micaela: OLED Display Integration

The Challenge: Add visual feedback to final HigiBox project. Display needs to show multiple screens (cycle status, stock, reminders) without blocking main code execution.

Hardware Setup

Component Connection Purpose
XIAO nRF52840 Main controller Runs display code and main logic
OLED SSD1306 0.96" I2C (D4 SDA, D5 SCL) 128×64 monochrome display, address 0x3C
Power 3.3V (XIAO supplies via headers) Display draws ~30 mA, well within GPIO limits

Why I2C Is Perfect Here

I2C uses only 2 wires (SDA + SCL) for data communication. The XIAO nRF52840 has native I2C on pins D4 (SDA) and D5 (SCL). Multiple devices can share same 2 wires if they have different addresses. OLED default address is 0x3C — no address conflicts with other Week 8 PCB components.

OLED display on custom PCB

OLED display integrated into custom PCB, showing real-time cycle information

6 Rotating Screens (5-Second Cycle)

  1. Welcome message with smiley face
  2. Stock alert with progress bar
  3. Low-stock warning message
  4. Current cycle day tracker
  5. Motivational reminder with heart icon
  6. Full stock status overview

Auto-cycling displays every 5 seconds using non-blocking millis() timing

✓ Key Achievement: 6 different screens rotating smoothly. Non-blocking design using millis() ensures display update doesn't freeze other operations (sensors, motor, logic). Each screen is purpose-built for HigiBox workflow.
👨 André: Servo Motor & Air Pump Testing

The Challenge: Evaluate different actuators for soft robotics application. Servo offers precision; air pump offers organic motion.

Option 1: Servo Motor Control

Tested servo motor positioning (0°, 90°, 180°) with LED feedback indicator.

Servo motor sweeping 0° → 90° → 180° with LED on during movement

Result: Servo works reliably and provides precise angular control. However, rigid arm motion doesn't align with soft robotics philosophy. Decided to pivot.

Option 2: Air Pump (Pneumatic Actuator) ⭐ SELECTED

After analyzing design goals, switched to pneumatic air pump for softer, more organic motion. Pump controlled via L298N motor driver (D0 IN1, D1 IN2).

DC air pump module

DC mini pump — generates pressure to inflate soft silicone structures

Air pump wiring diagram

Full circuit: XIAO + L298N driver + pump + 9V battery

Air pump ON for 3 seconds, OFF for 3 seconds. Controlled via L298N driver

⚡ Why Motor Driver Required?

GPIO pins max out at 15 mA output. Air pump needs 200–500 mA to operate. Without power amplification via L298N driver, motor receives insufficient current and stalls silently. The driver acts as intermediary — XIAO sends 3.3V logic signal to L298N, which switches 9V battery current to pump. Simple but critical.

Servo: Pros & Cons

✓ Precise positioning. ✗ Rigid motion. ✗ Requires power amplification for larger actuators.

Air Pump: Pros & Cons

✓ Soft, organic motion. ✓ Inflates flexible structures. ✗ Slower response. ✗ Requires pump + tubing + valve infrastructure.

📊 Device Comparison Table
Device Interface Current Req. Control Motion Type
DC Motor (Group) DRV8833 driver 0.15 A @ 100% PWM duty cycle Rotational, variable speed
OLED (Micaela) I2C (2 wires) ~30 mA Digital commands Display output, no motion
Servo (Andres) Direct GPIO (PWM) ~100 mA Angle command Angular, 0°–180°
Air Pump ⭐ L298N driver 300–500 mA ON/OFF or PWM Pneumatic, soft inflation

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