Add hardware shopping list with component recommendations

docs/SHOPPING_LIST.md

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+# Hardware Shopping List
+
+This document lists recommended components for building the ESP32 8-channel relay controller.
+
+## Essential Components
+
+### 1. ESP32 Development Board
+**Recommended:**
+- ESP32-DevKitC V4 (30-pin version)
+- ESP32-WROOM-32D Module
+- DOIT ESP32 DevKit V1
+
+**Specifications:**
+- Dual-core processor
+- Built-in WiFi + Bluetooth
+- Minimum 8 available GPIO pins
+- USB to Serial converter for programming
+
+**Where to Buy:**
+- AliExpress: $3-8 USD
+- Amazon: $10-15 USD
+- SparkFun/Adafruit: $20-25 USD
+
+### 2. 8-Channel Relay Module
+**Recommended Models:**
+- 8-Channel 5V Relay Module (Active LOW)
+- SainSmart 8-Channel Relay Board
+- Elegoo 8-Channel Relay Module
+
+**Specifications:**
+- Input voltage: 5V DC
+- Trigger: Active LOW (or Active HIGH - check specs)
+- Contact rating: 10A @ 250VAC, 10A @ 30VDC
+- Optocoupler isolation
+- LED indicators for each channel
+
+**Where to Buy:**
+- AliExpress: $5-10 USD
+- Amazon: $15-25 USD
+- eBay: $8-15 USD
+
+### 3. Power Supply
+**For ESP32:**
+- USB cable (Micro-USB or USB-C depending on board)
+- OR 5V 1A power adapter with micro-USB
+
+**For Relay Module:**
+- 5V 2A power supply (if driving all relays simultaneously)
+- OR use ESP32's 5V output for low-current applications
+
+**Recommended:**
+- 5V 3A USB power supply
+- Power bank (for portable/testing use)
+
+**Where to Buy:**
+- Any electronics store
+- $5-15 USD depending on current rating
+
+### 4. Wiring and Connectors
+
+**Jumper Wires:**
+- Male-to-Male: 20-30 pieces
+- Male-to-Female: 20-30 pieces
+- Female-to-Female: 10-20 pieces (optional)
+
+**Terminal Blocks:**
+- Screw terminals for relay outputs
+- 2-position or 3-position, 5mm pitch
+- Quantity: 8-16 pieces
+
+**Wire:**
+- 22 AWG solid core wire for prototyping
+- 18-20 AWG stranded wire for AC connections
+- Red (positive) and Black (ground/negative)
+
+**Where to Buy:**
+- Jumper wire set: $5-10 USD
+- Terminal blocks: $5-10 USD for set
+- Wire: $10-20 USD per spool
+
+## Optional but Recommended
+
+### 5. Prototyping
+- **Breadboard** (830 tie-points): $5-10 USD
+- **Soldering iron kit**: $20-40 USD
+- **Solder**: Lead-free, 60/40 tin-lead
+- **Heat shrink tubing**: Various sizes
+- **Wire strippers**: $10-20 USD
+
+### 6. Enclosure
+- **Project box** (suitable size for ESP32 + relay module)
+- Recommended: 200x120x75mm plastic enclosure
+- Ventilation holes for heat dissipation
+- **Price:** $10-20 USD
+
+### 7. Safety Components
+- **Fuses**: 2A-10A depending on load
+- **Fuse holders**: Panel mount or inline
+- **MOVs** (Metal Oxide Varistors) for surge protection
+- **DIN rail** for professional installation
+- **Price:** $15-30 USD for complete safety kit
+
+### 8. Testing Equipment
+- **Multimeter**: For testing connections and voltage
+- **Price:** $15-50 USD
+- **AC outlet tester**: For testing switched outlets
+- **Price:** $5-15 USD
+
+## Component Bundles
+
+Some sellers offer complete kits that include:
+- ESP32 board
+- 8-channel relay module
+- Jumper wires
+- Power supply
+
+**Typical bundle price:** $25-40 USD
+
+## Total Cost Estimate
+
+**Minimal Build:**
+- ESP32: $8
+- Relay Module: $10
+- Wiring: $10
+- Power Supply: $10
+- **Total: ~$38 USD**
+
+**Complete Build with Enclosure:**
+- ESP32: $10
+- Relay Module: $15
+- Wiring & Connectors: $15
+- Power Supply: $12
+- Enclosure: $15
+- Safety Components: $20
+- Tools (if needed): $30
+- **Total: ~$117 USD**
+
+**Professional Installation:**
+- All of the above
+- DIN rail mounting: $15
+- Professional enclosure: $30-50
+- Circuit breakers: $20-40
+- **Total: ~$200-250 USD**
+
+## Purchasing Tips
+
+1. **Buy from reputable sellers** - Check reviews before purchasing
+2. **Verify specifications** - Ensure relay voltage/current ratings match your needs
+3. **Order spare components** - ESP32 boards and relays can fail during development
+4. **Check shipping times** - AliExpress is cheaper but slower (2-6 weeks)
+5. **Local electronics stores** - More expensive but immediate availability
+
+## Alternatives and Variations
+
+### 4-Channel Version
+If you only need 4 relays:
+- Use 4-channel relay module ($5-8)
+- Reduced GPIO requirements
+- Smaller enclosure needed
+
+### 16-Channel Version
+To control 16 relays:
+- Use two 8-channel modules
+- May require I2C relay controller boards
+- Separate power supply for each module
+
+### WiFi Control Version
+Add WiFi control capability:
+- Use ESP32's built-in WiFi
+- Requires additional firmware (ESPHome, Tasmota, or custom)
+- No additional hardware needed
+
+## Where to Buy - Recommended Vendors
+
+**International Shipping:**
+- AliExpress (cheapest, slow shipping)
+- Banggood
+- eBay
+
+**Fast Shipping (US):**
+- Amazon
+- SparkFun
+- Adafruit
+- DigiKey
+- Mouser
+
+**Australia:**
+- Core Electronics
+- Jaycar Electronics
+- Little Bird Electronics
+
+**Europe:**
+- RS Components
+- Farnell
+- Conrad Electronic
+
+**Always compare prices across vendors and factor in shipping costs!**
+
+## Version Information
+
+**Document Version:** 1.0  
+**Last Updated:** December 2025  
+**Currency:** USD (prices approximate and subject to change)