24  Quick Reference Cards

Condensed Cheat Sheets for IoT Development

24.1 Quick Reference Cards

TipPrint-Ready Reference

These cards are designed to be printed or kept open as quick references during development. Each card fits on a single page.

24.2 Protocol Quick Reference

24.2.1 MQTT Cheat Sheet

24.2.2 CoAP Cheat Sheet

24.2.3 BLE Cheat Sheet

24.2.4 LoRaWAN Cheat Sheet

24.3 Formula Reference

24.4 Pin-Out Reference

24.4.1 ESP32 Quick Reference

24.5 Common Patterns

24.5.1 Sensor Reading Pattern

# Pseudo-code for robust sensor reading
def read_sensor_with_retry(sensor, max_retries=3):
    for attempt in range(max_retries):
        try:
            value = sensor.read()
            if is_valid(value):
                return value
        except SensorError:
            time.sleep(0.1 * (2 ** attempt))  # Exponential backoff
    return None  # Or raise exception

# Moving average filter
class MovingAverage:
    def __init__(self, window=10):
        self.window = window
        self.values = []

    def add(self, value):
        self.values.append(value)
        if len(self.values) > self.window:
            self.values.pop(0)
        return sum(self.values) / len(self.values)

24.5.2 MQTT Connection Pattern

# Robust MQTT connection with reconnection
def connect_mqtt(client, broker, port=1883):
    def on_connect(client, userdata, flags, rc):
        if rc == 0:
            client.subscribe("device/+/command")
        else:
            print(f"Connection failed: {rc}")

    def on_disconnect(client, userdata, rc):
        while True:
            try:
                client.reconnect()
                break
            except:
                time.sleep(5)

    client.on_connect = on_connect
    client.on_disconnect = on_disconnect
    client.connect(broker, port, keepalive=60)

24.5.3 Deep Sleep Pattern

# ESP32 deep sleep with wake sources
import machine
import esp32

def enter_deep_sleep(seconds):
    # Configure wake sources
    esp32.wake_on_ext0(pin=machine.Pin(0), level=esp32.WAKEUP_ALL_LOW)

    # Set timer wake
    machine.deepsleep(seconds * 1000)

# Check wake reason
wake_reason = machine.wake_reason()
if wake_reason == machine.PIN_WAKE:
    handle_button_press()
elif wake_reason == machine.TIMER_WAKE:
    send_sensor_data()

24.6 Conversion Tables