Capstone 4: Home Automation Hub

Protocol Comparison

Hardware Architecture

flowchart TD
    A["ESP32-S3
Main Controller
WiFi + BLE"] --> B["CC2652R
Zigbee 3.0
+ Thread"]
    A -->|UART| B
    A --> C["eMMC
8GB Storage"]
    A --> D["Ethernet
W5500 (SPI)"]
    A --> E["USB-C
Power + Debug"]
    B --> F["PCB Antenna
2.4GHz Zigbee"]
    A --> G["PCB Antenna
2.4GHz WiFi/BLE"]
    A --> H["Status LEDs
RGB × 3"]
    A --> I["Local Web UI
mDNS + REST"]
    style A fill:#3B9797,color:#fff
    style B fill:#16476A,color:#fff
                            

# Home automation hub BOM — multi-protocol gateway
# Prices in USD at qty 100

bom = [
    ("ESP32-S3-WROOM-1",  "Dual-core 240MHz, WiFi+BLE5",    3.90, 1),
    ("CC2652R",            "Zigbee 3.0 + Thread radio",       4.50, 1),
    ("W5500",              "Ethernet SPI controller",          2.10, 1),
    ("eMMC 8GB",           "KLMAG1JETD-B041 storage",         3.80, 1),
    ("USB-C PD sink",      "FUSB302 + 5V/3A negotiation",     1.20, 1),
    ("LDO 3.3V",           "AMS1117-3.3, 1A",                 0.15, 2),
    ("LDO 1.8V",           "AP7361C-18, for CC2652",          0.25, 1),
    ("Crystal 32.768kHz",  "For RTC and Zigbee timing",       0.30, 2),
    ("RJ45 + magnetics",   "Ethernet jack with transformer",  1.80, 1),
    ("PCB 4-layer",        "80x80mm, ENIG, impedance ctrl",   2.60, 1),
    ("ABS Enclosure",      "Desktop mount, 100x100x30mm",     2.20, 1),
    ("Passives",           "Caps, resistors, RF matching",     1.50, 1),
]

print("Home Automation Hub BOM — Qty 100")
print("=" * 65)
print(f"{'Component':<22} {'Description':<33} {'Qty':>3} {'Unit $':>7}")
print("-" * 65)

total = 0
for name, desc, price, qty in bom:
    line_total = price * qty
    total += line_total
    print(f"{name:<22} {desc:<33} {qty:>3} ${price:>6.2f}")

print("-" * 65)
print(f"{'TOTAL BOM':<58} ${total:>6.2f}")
print(f"\nWith assembly + test: ${total * 1.25:.2f}")

RF Design Considerations

# RF coexistence analysis — channel allocation strategy
# 2.4 GHz band: 2400-2483.5 MHz

protocols = {
    "WiFi Ch 1":   {"center": 2412, "bw": 22, "color": "blue"},
    "WiFi Ch 6":   {"center": 2437, "bw": 22, "color": "blue"},
    "WiFi Ch 11":  {"center": 2462, "bw": 22, "color": "blue"},
    "Zigbee Ch 15": {"center": 2425, "bw": 2, "color": "green"},
    "Zigbee Ch 20": {"center": 2450, "bw": 2, "color": "green"},
    "Zigbee Ch 25": {"center": 2475, "bw": 2, "color": "green"},
    "BLE Adv Ch37": {"center": 2402, "bw": 2, "color": "red"},
    "BLE Adv Ch38": {"center": 2426, "bw": 2, "color": "red"},
    "BLE Adv Ch39": {"center": 2480, "bw": 2, "color": "red"},
}

print("2.4 GHz RF Coexistence Map")
print("=" * 60)
print(f"{'Protocol':<18} {'Center MHz':>10} {'BW MHz':>7} {'Range':>20}")
print("-" * 60)

for name, spec in protocols.items():
    lo = spec["center"] - spec["bw"] // 2
    hi = spec["center"] + spec["bw"] // 2
    print(f"{name:<18} {spec['center']:>10} {spec['bw']:>7} {lo}-{hi} MHz")

print("\nRecommended coexistence strategy:")
print("  WiFi:   Fix to Channel 1 (2401-2423 MHz)")
print("  Zigbee: Use Channel 25 (2474-2476 MHz) — minimal WiFi overlap")
print("  BLE:    Adaptive frequency hopping avoids occupied channels")
print("  TDM:    Zigbee TX window: 5ms every 100ms (5% duty cycle)")

Protocol Bridge Firmware

/* Unified device model — protocol-agnostic abstraction layer
   Bridges Zigbee, BLE Mesh, and WiFi devices */

#include <stdint.h>

typedef enum {
    PROTO_ZIGBEE,
    PROTO_BLE_MESH,
    PROTO_WIFI,
    PROTO_THREAD,
} protocol_t;

typedef enum {
    DEV_LIGHT,
    DEV_SWITCH,
    DEV_SENSOR,
    DEV_THERMOSTAT,
    DEV_LOCK,
} device_type_t;

typedef struct {
    uint64_t    ieee_addr;       /* Unique 64-bit device address */
    protocol_t  protocol;        /* Source protocol */
    device_type_t type;          /* Normalized device type */
    uint8_t     online;          /* 1 = reachable */
    uint32_t    last_seen;       /* Timestamp (epoch seconds) */
    char        name[32];        /* User-friendly name */
    /* Generic state union */
    union {
        struct { uint8_t on; uint8_t brightness; uint16_t color_temp; } light;
        struct { uint8_t state; } sw;
        struct { int16_t temperature; uint16_t humidity; } sensor;
        struct { int16_t setpoint; int16_t current; uint8_t mode; } thermo;
    } state;
} unified_device_t;

/* Device registry — up to 128 devices */
#define MAX_DEVICES 128
unified_device_t device_registry[MAX_DEVICES];
uint16_t device_count;

/* Automation rule example:
 * IF sensor.temperature > 25°C THEN light.on = 1
 * Rules stored in eMMC, evaluated every 1s
 */

Device Planner

Conclusion

The home automation hub capstone integrates multi-radio hardware design, RF coexistence engineering, and protocol bridging firmware. The ESP32-S3 + CC2652R combination covers WiFi, BLE, Zigbee, and Thread — with Matter support enabling future-proof interoperability across all major smart home ecosystems.