Module 11: Arduino Nano & Compact Builds

Level: 🟡 Intermediate
Board: Arduino Nano
Prerequisites: Module 8
Estimated time: 60–80 minutes
Goal: Build compact, portable projects and understand board selection.

What You'll Learn

The Arduino Uno is great for learning, but it's too bulky for most finished projects. The Arduino Nano is pin-compatible with the Uno, fits directly on a breadboard, and costs less. In this module you'll learn the Nano's differences, deal with USB drivers, solder headers, choose portable power, plan compact builds for enclosures, and put it all together with a battery-powered portable air quality monitor.

11.1 Nano vs. Uno: What's Different and What's the Same

Hardware Comparison

Pin Mapping: What Moves

The pin functions are identical, but the physical locations change:

• Digital pins 0–13: Same numbering, different physical positions along the Nano's edges
• Analog pins A0–A5: Same as Uno
• A6 and A7: Nano-only, analog input only (cannot be used as digital pins)
• 5V, 3.3V, GND, VIN, RESET: All present, same function
• AREF: Available for analog reference voltage

Key point: Any Uno sketch runs on a Nano without code changes. The pins are numbered the same. Only the physical wiring layout changes.

Power Differences

The Nano has no barrel jack. For external power, use the VIN pin (accepts 6.5–12V, regulated down to 5V) or feed regulated 5V directly to the 5V pin.

11.2 USB Drivers: CH340 vs. FTDI

The Driver Problem

Official Arduino Nanos use the FTDI FT232RL USB-to-serial chip. Most affordable clones use the CH340G chip instead. The CH340G requires a separate driver installation on some operating systems.

How to Know Which You Have

Look at the small IC near the USB connector:

• FTDI FT232RL: Square chip, labeled "FT232RL" or "FTDI"
• CH340G: Rectangular chip, labeled "CH340G"

Installing CH340 Drivers

Windows: Usually auto-installs via Windows Update. If not, download from the CH340 manufacturer's website.

macOS: Older macOS versions need a manual driver. macOS 12+ typically includes it. If your Nano isn't recognized, search "CH340 macOS driver" for the current installer.

Linux: CH340 support is built into the kernel since around 2014. Should work automatically.

Troubleshooting USB Connection

The Old Bootloader trick: Many Nano clones use an older bootloader. If upload fails with "not in sync," go to Tools → Processor and select "ATmega328P (Old Bootloader)". This is the single most common Nano issue.

11.3 Soldering Headers

Many Nano boards arrive without headers soldered. You'll need to solder them yourself to use the board with a breadboard.

Tools Needed

Step-by-Step Header Soldering

1. Prepare:

• Insert the header pins into a breadboard (long pins down)
• Place the Nano on top, aligning the holes with the short pins sticking up
• The breadboard holds everything aligned while you solder

2. Tack corners first:

• Solder one corner pin on each side
• Check alignment: the Nano should sit flat and straight
• If crooked, reheat the tacked pin and adjust

3. Solder remaining pins:

• Touch the iron tip to both the pin and the pad simultaneously
• Feed solder into the joint (not onto the iron)
• Hold for 2–3 seconds; solder should flow around the pin and form a smooth cone
• Move to the next pin

4. Inspect:

• Every joint should be a shiny, smooth cone (not a dull blob)
• No bridges between adjacent pins
• Test every pin with continuity meter

Common Soldering Mistakes

Safety

• Work in a ventilated area; solder fumes are irritating
• Don't touch the iron tip (300°C+)
• Use a stand for the iron when not holding it
• Wash hands after soldering (especially with leaded solder)
• Wear safety glasses; solder can occasionally spit

11.4 Portable Power Options

Battery Options for Nano Projects

Power Bank Auto-Shutoff Problem

Many USB power banks detect low current draw and turn off, thinking the device is fully charged. A basic Arduino Nano draws only ~20 mA, below the detection threshold of many power banks.

Solutions:

• Use a power bank that supports low-current mode (check reviews)
• Add a small resistive load (a 100Ω resistor across 5V and GND draws 50 mA, but wastes battery)
• Use a dedicated battery + regulator instead

Calculating Battery Runtime

Runtime (hours) = Battery capacity (mAh) / Current draw (mA)

Example: Nano (20 mA) + OLED (20 mA) + MQ-135 sensor (150 mA) = 190 mA total

With 4×AA batteries (2500 mAh): 2500 / 190 ≈ 13 hours

With a 2000 mAh 18650 + boost converter (85% efficient): (2000 × 0.85) / 190 ≈ 9 hours

Always measure actual current draw with a multimeter rather than relying on datasheet values. Actual consumption often differs from specifications.

11.5 Designing for Enclosures

Planning Before Building

Before you build the circuit, plan the enclosure:

1. Measure everything:

• Board dimensions (Nano: 45 × 18 mm)
• Component heights (OLED: ~4 mm above board, sensor: varies)
• Cable clearance for USB connector
• Sensor openings (air quality sensors need airflow)

2. Sketch the layout:

• Draw the interior of your enclosure
• Place components to minimize wire length
• Plan where power switch and USB access will be
• Mark where the display faces outward
• Ensure sensor has access to air/light/whatever it measures

3. Access considerations:

• USB port for reprogramming and charging
• Power switch (SPST toggle or slide switch between battery + and VIN)
• Reset button access (or add an external reset button)
• Sensor exposure (don't seal a gas sensor inside an airtight box)

Enclosure Options

Wire Management

• Use short, solid-core wires for internal connections
• Color-code: red = power, black = ground, others = signals
• Add strain relief where wires pass through enclosure walls (hot glue works)
• Leave enough slack to open the enclosure without pulling wires
• Label internal connections if they aren't obvious

Module Project: Portable Air Quality Monitor

Objective

Build a battery-powered portable monitor using the Arduino Nano, MQ-135 gas sensor, DHT22 for temperature/humidity, and SSD1306 OLED display. The finished project should be compact enough to fit in a small enclosure.

Components Needed

Important: MQ-135 Considerations

The MQ-135 contains a heater element that must warm up for accurate readings:

• Warm-up time: 24–48 hours for initial calibration (seriously), 2–5 minutes for approximate readings
• Current draw: ~150 mA (most of the power budget!)
• Output: Analog voltage proportional to gas concentration
• Sensitivity: Responds to multiple gases, not specific enough for precise measurement, but good for "air quality index" approximation

Calibration note: The MQ-135 is not a precision instrument. It gives a relative reading ("better" or "worse" air quality), not exact PPM values. For this project, we'll create a relative scale and track changes over time.

Wiring

Power routing: The MQ-135 draws 150 mA, which is significant. On battery power via VIN, the Nano's regulator handles everything. On USB power, ensure total current stays within USB limits.

The Code

/*
 * Module 11 Project: Portable Air Quality Monitor
 *
 * Arduino Nano with:
 * - MQ-135 gas sensor → A0
 * - DHT22 → D2 (10kΩ pull-up)
 * - SSD1306 OLED → A4 (SDA), A5 (SCL)
 * - Battery powered via VIN (4×AA through switch)
 *
 * Libraries: Adafruit SSD1306, Adafruit GFX, DHT
 * Board: Arduino Nano (ATmega328P or Old Bootloader)
 */

#include <Wire.h>
#include <Adafruit_SSD1306.h>
#include <DHT.h>

// --- Pins ---
const int MQ135_PIN = A0;
const int DHT_PIN = 2;

// --- Sensors ---
DHT dht(DHT_PIN, DHT22);

// --- OLED ---
#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64
Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, -1);

// --- Air quality baseline ---
// After warm-up, read the sensor in clean air to set baseline
int airBaseline = 0;
bool baselineSet = false;
const unsigned long WARMUP_TIME = 120000;  // 2 minutes (minimum for approximate readings)

// --- Smoothing ---
float smoothedAir = 0;
float smoothedTemp = 0;
float smoothedHumidity = 0;
const float ALPHA = 0.15;
bool firstReading = true;

// --- Timing ---
unsigned long lastSensorRead = 0;
const unsigned long SENSOR_INTERVAL = 2000;
unsigned long lastDisplayUpdate = 0;
const unsigned long DISPLAY_INTERVAL = 500;

// --- History (last 64 readings for graph) ---
int airHistory[64];
int historyIndex = 0;
bool historyFull = false;

// --- Battery voltage monitoring ---
// Read VIN through the voltage divider on the Nano (A7 on some clones)
// This is approximate — varies by board

void drawProgressBar(int x, int y, int w, int h, int percent, bool invert) {
  percent = constrain(percent, 0, 100);
  display.drawRect(x, y, w, h, SSD1306_WHITE);
  int fillW = (w - 2) * percent / 100;
  if (invert) fillW = (w - 2) - fillW;
  display.fillRect(x + 1, y + 1, fillW, h - 2, SSD1306_WHITE);
}

String getAirQualityLabel(int reading) {
  if (!baselineSet) return "Warming up...";

  int diff = reading - airBaseline;

  if (diff < 20) return "Good";
  else if (diff < 80) return "Moderate";
  else if (diff < 150) return "Poor";
  else return "Unhealthy";
}

int getAirQualityPercent(int reading) {
  if (!baselineSet) return 0;
  int diff = reading - airBaseline;
  return constrain(map(diff, 0, 300, 100, 0), 0, 100);
}

void drawMiniGraph(int x, int y, int w, int h) {
  display.drawRect(x, y, w, h, SSD1306_WHITE);

  int count = historyFull ? 64 : historyIndex;
  if (count < 2) return;

  // Find min/max for scaling
  int minVal = 1023, maxVal = 0;
  for (int i = 0; i < count; i++) {
    if (airHistory[i] < minVal) minVal = airHistory[i];
    if (airHistory[i] > maxVal) maxVal = airHistory[i];
  }
  if (maxVal == minVal) maxVal = minVal + 1;

  // Draw points
  for (int i = 0; i < count && i < w - 2; i++) {
    int idx = historyFull ? (historyIndex + i) % 64 : i;
    int py = map(airHistory[idx], minVal, maxVal, y + h - 2, y + 1);
    display.drawPixel(x + 1 + i, py, SSD1306_WHITE);
  }
}

void updateDisplay() {
  display.clearDisplay();
  unsigned long now = millis();

  // --- Header ---
  display.setTextSize(1);
  display.setCursor(0, 0);
  display.print("Air Monitor");

  // Warm-up indicator
  if (!baselineSet) {
    int warmPercent = constrain(now * 100 / WARMUP_TIME, 0, 100);
    display.setCursor(75, 0);
    display.print("W:");
    display.print(warmPercent);
    display.print("%");
  }

  display.drawLine(0, 9, 127, 9, SSD1306_WHITE);

  // --- Air quality ---
  display.setTextSize(1);
  display.setCursor(0, 12);
  display.print("Air: ");

  String label = getAirQualityLabel((int)smoothedAir);
  display.print(label);

  int aqPercent = getAirQualityPercent((int)smoothedAir);
  drawProgressBar(0, 22, 80, 7, aqPercent, false);

  display.setCursor(84, 22);
  display.print((int)smoothedAir);

  // --- Temperature & Humidity ---
  display.setCursor(0, 33);
  display.print("T:");
  display.print(smoothedTemp, 1);
  display.print("C");

  display.setCursor(64, 33);
  display.print("H:");
  display.print(smoothedHumidity, 0);
  display.print("%");

  // --- Mini history graph ---
  drawMiniGraph(0, 43, 64, 20);

  // --- Uptime ---
  display.setCursor(70, 55);
  unsigned long secs = now / 1000;
  char timeStr[10];
  sprintf(timeStr, "%02lu:%02lu:%02lu", secs / 3600, (secs % 3600) / 60, secs % 60);
  display.print(timeStr);

  display.display();
}

void setup() {
  Serial.begin(9600);
  dht.begin();

  // Initialize history
  for (int i = 0; i < 64; i++) airHistory[i] = 0;

  // OLED
  if (!display.begin(SSD1306_SWITCHCAPVCC, 0x3C)) {
    Serial.println("OLED not found");
    while (1);
  }

  display.clearDisplay();
  display.setTextColor(SSD1306_WHITE);
  display.setTextSize(1);
  display.setCursor(5, 10);
  display.println("Portable Air");
  display.println("  Quality Monitor");
  display.println();
  display.println("  Warming up sensor");
  display.println("  Please wait 2 min");
  display.display();

  Serial.println("Air Quality Monitor — Module 11");
  Serial.println("MQ-135 warming up...");
}

void loop() {
  unsigned long now = millis();

  // --- Read sensors ---
  if (now - lastSensorRead >= SENSOR_INTERVAL) {
    lastSensorRead = now;

    // Air quality
    int airRaw = analogRead(MQ135_PIN);

    // DHT22
    float t = dht.readTemperature();
    float h = dht.readHumidity();

    // Smooth
    if (firstReading) {
      smoothedAir = airRaw;
      if (!isnan(t)) smoothedTemp = t;
      if (!isnan(h)) smoothedHumidity = h;
      firstReading = false;
    } else {
      smoothedAir = (ALPHA * airRaw) + ((1 - ALPHA) * smoothedAir);
      if (!isnan(t)) smoothedTemp = (ALPHA * t) + ((1 - ALPHA) * smoothedTemp);
      if (!isnan(h)) smoothedHumidity = (ALPHA * h) + ((1 - ALPHA) * smoothedHumidity);
    }

    // Set baseline after warm-up
    if (!baselineSet && now >= WARMUP_TIME) {
      airBaseline = (int)smoothedAir;
      baselineSet = true;
      Serial.print("Baseline set: ");
      Serial.println(airBaseline);
    }

    // Record history
    airHistory[historyIndex] = (int)smoothedAir;
    historyIndex = (historyIndex + 1) % 64;
    if (historyIndex == 0) historyFull = true;

    // Serial CSV output
    Serial.print(now / 1000);
    Serial.print(",");
    Serial.print(airRaw);
    Serial.print(",");
    Serial.print(smoothedTemp, 1);
    Serial.print(",");
    Serial.println(smoothedHumidity, 1);
  }

  // --- Update display ---
  if (now - lastDisplayUpdate >= DISPLAY_INTERVAL) {
    lastDisplayUpdate = now;
    updateDisplay();
  }
}

Circuit Diagram (SVG)

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  <text x="100" y="148" text-anchor="middle" fill="white" font-size="13" font-weight="bold">Arduino</text>
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  <!-- USB -->
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  <!-- Pins -->
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  <text x="161" y="182" text-anchor="middle" fill="white" font-size="7">GND</text>
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  <text x="161" y="259" text-anchor="middle" fill="white" font-size="7">D2</text>
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  <text x="161" y="289" text-anchor="middle" fill="white" font-size="7">A4</text>
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  <text x="161" y="309" text-anchor="middle" fill="white" font-size="7">A5</text>

  <!-- Battery + Switch -->
  <rect x="250" y="120" width="90" height="55" fill="#dd9933" stroke="#333" stroke-width="2" rx="6"/>
  <text x="295" y="142" text-anchor="middle" fill="white" font-size="10" font-weight="bold">4×AA</text>
  <text x="295" y="158" text-anchor="middle" fill="white" font-size="9">6V</text>

  <rect x="355" y="132" width="50" height="22" fill="#999" stroke="#333" stroke-width="1.5" rx="4"/>
  <text x="380" y="147" text-anchor="middle" font-size="8" fill="white">Switch</text>

  <line x1="340" y1="140" x2="355" y2="140" stroke="red" stroke-width="2"/>
  <line x1="405" y1="140" x2="440" y2="140" stroke="red" stroke-width="2"/>
  <line x1="440" y1="140" x2="440" y2="161" stroke="red" stroke-width="2"/>
  <line x1="440" y1="161" x2="172" y2="161" stroke="red" stroke-width="2"/>
  <text x="300" y="100" font-size="9" fill="red">Battery + → Switch → VIN</text>

  <line x1="250" y1="165" x2="250" y2="179" stroke="blue" stroke-width="2"/>
  <line x1="250" y1="179" x2="172" y2="179" stroke="blue" stroke-width="2"/>

  <!-- MQ-135 -->
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  <text x="400" y="232" text-anchor="middle" fill="white" font-size="11" font-weight="bold">MQ-135</text>
  <text x="400" y="250" text-anchor="middle" fill="white" font-size="8">Air Quality</text>
  <text x="400" y="260" text-anchor="middle" fill="#ffaa88" font-size="7">~150 mA!</text>

  <line x1="172" y1="231" x2="350" y2="231" stroke="green" stroke-width="1.5"/>
  <text x="260" y="226" font-size="8" fill="green">AOUT (A0)</text>

  <line x1="172" y1="201" x2="350" y2="220" stroke="red" stroke-width="1"/>
  <line x1="172" y1="179" x2="350" y2="255" stroke="blue" stroke-width="1"/>

  <!-- DHT22 -->
  <rect x="350" y="290" width="100" height="45" fill="#4488aa" stroke="#333" stroke-width="2" rx="6"/>
  <text x="400" y="312" text-anchor="middle" fill="white" font-size="10" font-weight="bold">DHT22</text>
  <text x="400" y="328" text-anchor="middle" fill="white" font-size="8">Temp+Humidity</text>

  <line x1="172" y1="256" x2="350" y2="308" stroke="green" stroke-width="1.5"/>
  <text x="260" y="280" font-size="8" fill="green">DATA (D2)</text>

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  <text x="298" y="304" text-anchor="middle" font-size="7">10kΩ↑</text>

  <!-- OLED -->
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  <text x="595" y="210" text-anchor="middle" fill="#00ccff" font-size="10">Air: Good</text>
  <text x="595" y="222" text-anchor="middle" fill="#00ccff" font-size="8">▓▓▓▓▓▓▓░░ 78%</text>
  <text x="595" y="234" text-anchor="middle" fill="#00ccff" font-size="8">T:23.5 H:52%</text>
  <text x="595" y="258" text-anchor="middle" fill="white" font-size="9">SSD1306 OLED</text>

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  <text x="635" y="330" text-anchor="middle" font-size="10" font-weight="bold">Form Factor</text>
  <text x="560" y="348" font-size="8">Nano: 45×18mm</text>
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Circuit Schema (JSON)

{
  "module": 11,
  "project": "Portable Air Quality Monitor",
  "board": "Arduino Nano",
  "schematic": {
    "components": [
      {
        "id": "U1", "type": "arduino_nano",
        "pins_used": {
          "VIN": "net_vin", "GND": "net_gnd", "5V": "net_5v",
          "A0": "net_mq_aout", "D2": "net_dht_data",
          "A4": "net_sda", "A5": "net_scl"
        }
      },
      { "id": "BAT1", "type": "battery_pack", "value": "6V", "description": "4×AA",
        "pins": { "positive": "net_bat_pos", "negative": "net_gnd" } },
      { "id": "SW1", "type": "spst_switch", "purpose": "Power on/off",
        "pins": { "pin1": "net_bat_pos", "pin2": "net_vin" } },
      { "id": "MQ1", "type": "mq135", "current_draw": "150mA", "warmup": "2-5 min approximate",
        "pins": { "vcc": "net_5v", "gnd": "net_gnd", "aout": "net_mq_aout" } },
      { "id": "DHT1", "type": "dht22",
        "pins": { "vcc": "net_5v", "data": "net_dht_data", "gnd": "net_gnd" } },
      { "id": "R1", "type": "resistor", "value": "10000", "unit": "ohm",
        "purpose": "DHT22 data pull-up",
        "pins": { "pin1": "net_5v", "pin2": "net_dht_data" } },
      { "id": "OLED1", "type": "ssd1306", "address": "0x3C",
        "pins": { "vcc": "net_5v", "gnd": "net_gnd", "sda": "net_sda", "scl": "net_scl" } }
    ],
    "nets": [
      { "name": "net_gnd", "nodes": ["U1.GND", "BAT1.negative", "MQ1.gnd", "DHT1.gnd", "OLED1.gnd"] },
      { "name": "net_vin", "nodes": ["U1.VIN", "SW1.pin2"] },
      { "name": "net_bat_pos", "nodes": ["BAT1.positive", "SW1.pin1"] },
      { "name": "net_5v", "nodes": ["U1.5V", "MQ1.vcc", "DHT1.vcc", "R1.pin1", "OLED1.vcc"] },
      { "name": "net_mq_aout", "nodes": ["U1.A0", "MQ1.aout"] },
      { "name": "net_dht_data", "nodes": ["U1.D2", "DHT1.data", "R1.pin2"] },
      { "name": "net_sda", "nodes": ["U1.A4", "OLED1.sda"] },
      { "name": "net_scl", "nodes": ["U1.A5", "OLED1.scl"] }
    ],
    "power": {
      "source": "4×AA via VIN (6V, regulated to 5V internally)",
      "total_current_ma": 193,
      "breakdown": "Nano(23) + MQ-135(150) + DHT22(2.5) + OLED(17.5)",
      "estimated_runtime": "~13 hours on 2500mAh AA batteries"
    }
  },
  "code": { "filename": "module11_air_monitor.ino", "language": "cpp" },
  "validation": {
    "expected_behavior": "OLED shows air quality level with bar and history graph, temp, humidity. MQ-135 warms up for 2 min, then sets baseline.",
    "common_mistakes": [
      "Upload fails: select 'ATmega328P (Old Bootloader)' in Tools → Processor",
      "No port appears: install CH340 driver for your OS",
      "MQ-135 reads constant 0 or 1023: sensor not powered, or AOUT not connected to A0",
      "Air readings never change: sensor hasn't warmed up yet (needs 2+ minutes minimum)",
      "Battery dies fast: MQ-135 draws 150mA — calculated runtime is correct, consider larger battery",
      "Power bank keeps shutting off: current draw may be too low during idle periods"
    ]
  }
}

Self-Check: Module 11

Before moving to Module 12, make sure you can:

• Explain the key differences and similarities between Nano and Uno
• Install CH340 drivers and resolve the "Old Bootloader" upload issue
• Solder header pins onto a Nano (clean, cone-shaped joints, no bridges)
• Choose an appropriate battery for a given project's power needs
• Calculate expected battery runtime from component current draws
• Plan a compact layout suitable for an enclosure
• Build the portable air quality monitor with battery power and display

Key Terms Glossary

Previous: ← Module 10: Motors & Movement Next: Module 12: Troubleshooting & Debugging: The Essential Skill →