Architecture Overview

The ESL MQTT API system is designed with a hierarchical architecture that supports both direct WiFi connections and gateway-routed BLE connections. This flexible design allows for scalable deployments from small stores to large retail chains.

Key Design Principles:
  • Hierarchical message routing
  • Support for mixed connectivity (WiFi + BLE)
  • Scalable mesh network architecture
  • Centralized management with distributed execution

Network Topology

Direct Connection Architecture: WiFi ESLs connect directly to the server via Internet, eliminating gateway dependency for critical devices and ensuring real-time updates.

Server Layer

Central Server
Source of Truth
API Management
Data Storage
↕ Internet Connection

Direct WiFi Connection

WiFi ESLs
ESP32-S3 Series
Direct Server Connection
Real-time Updates

Gateway Layer

Main Gateway
ESP32-S3
Internet Bridge
BLE Coordinator
Mesh Gateways
ESP32-C3
Zone Coverage
BLE Bridge
↕ BLE Connections

BLE ESL Layer

BLE ESLs
nRF52832
Gateway-routed
4+ Year Battery Life

Connection Types

Connection Hardware Protocol Characteristics
Server ↔ WiFi ESL ESP32-S3 Series MQTT over TCP/IP Direct connection, Real-time updates, No gateway dependency
Server ↔ Main Gateway ESP32-S3 MQTT over TCP/IP Bidirectional, Always-on, High bandwidth
Main Gateway ↔ Mesh Gateway ESP32-S3 ↔ ESP32-C3 802.11s mesh Self-healing, Multi-hop capable
Gateway ↔ BLE ESL ESP32-C3 ↔ nRF52832 BLE 5.0+ Ultra-low power, 4+ year battery, Scheduled connections

Connection Details

🌐 Direct WiFi Connections

ESP32-S3 series ESLs connect directly to server, bypassing gateways for critical applications.

  • Persistent MQTT connections
  • TLS encryption supported
  • Real-time price updates
  • Automatic reconnection
  • Suitable for high-value items

📡 Gateway Network

ESP32-S3 main gateways coordinate with ESP32-C3 mesh gateways for BLE device coverage.

  • 802.11s mesh protocol
  • Self-configuring topology
  • Automatic failover
  • Zone-based deployment

📶 BLE Connections

nRF52832-based ESLs provide ultra-low power operation with 4+ year battery life.

  • BLE 5.0+ features
  • Extended advertising
  • Scheduled wake cycles
  • 4+ year battery target
  • Cost-effective mass deployment

System Components

Central Server

The server acts as the central management system and source of truth for all ESL operations.

Responsibilities:

  • Store and manage ESL configurations
  • Generate and distribute display content
  • Schedule update operations
  • Monitor device status and health
  • Provide API endpoints for external systems
  • Handle error logging and analytics

Key Features:

🗄️ Data Management

Centralized database for device info, content, and schedules

🔐 Security

Authentication, encryption, and access control

📊 Analytics

Performance monitoring and reporting

🔄 Integration

APIs for POS, ERP, and pricing systems

Main Gateway

The main gateway serves as the primary bridge between the server and the local ESL network.

Responsibilities:

  • Maintain persistent connection to server
  • Route messages between server and ESL devices
  • Manage mesh network topology
  • Cache messages for offline devices
  • Coordinate bulk operations
  • Local BLE device management

Hardware Specifications:

ESP32-S3 Based Gateway:
  • CPU: Dual-core Xtensa LX7 @ 240MHz
  • RAM: 512KB SRAM + 8MB PSRAM
  • Storage: 16MB Flash for firmware and caching
  • WiFi: 802.11 b/g/n with mesh support
  • Bluetooth: BLE 5.0 + Bluetooth Classic
  • Power: PoE+ or 12V DC input
  • Operating Temperature: -40°C to +85°C

Mesh Gateway

Mesh gateways extend the network coverage and provide local BLE connectivity in different zones.

Responsibilities:

  • Connect to main gateway via WiFi mesh
  • Manage local BLE ESL devices
  • Handle scheduled device wake-ups
  • Buffer messages for sleeping devices
  • Report device status upstream
  • Local retry logic for failed transmissions

Hardware Specifications:

ESP32-C3 Based Gateway:
  • CPU: Single-core RISC-V @ 160MHz
  • RAM: 400KB SRAM
  • Storage: 4MB Flash for firmware
  • WiFi: 802.11 b/g/n with mesh support
  • Bluetooth: BLE 5.0
  • Power: PoE or 5V DC input
  • Cost-optimized for mass deployment

Deployment Considerations:

1
Coverage Planning

Each ESP32-C3 gateway covers approximately 30-50m radius for BLE devices

2
Capacity Limits

Recommended maximum of 50 BLE devices per ESP32-C3 gateway

3
Power Supply

PoE recommended for reliable operation and easy deployment

ESL Devices

Electronic Shelf Labels are the end devices that display pricing and product information.

Device Types:

📱 WiFi-Enabled ESLs
ESP32-S3 Series Based:
  • CPU: Dual-core Xtensa LX7 @ 240MHz
  • RAM: 512KB SRAM + up to 8MB PSRAM
  • WiFi: 802.11 b/g/n
  • Direct Internet connectivity
  • Real-time updates
  • Suitable for high-value items
  • Built-in web server for config
  • TLS encryption support
  • Advanced power management
📟 BLE-Only ESLs
nRF52832 Based:
  • CPU: ARM Cortex-M4F @ 64MHz
  • RAM: 64KB
  • Flash: 512KB
  • BLE 5.0 with extended advertising
  • Gateway-routed communication
  • Ultra-low power consumption
  • Scheduled wake-up cycles
  • 4+ year battery life target
  • Cost-effective for mass deployment

Battery Life Optimization (nRF52832 ESLs):

🔋 Power Management

Advanced sleep modes with RAM retention and ultra-low standby current (<1µA)

⏰ Wake Scheduling

Configurable wake intervals (1-24 hours) based on update frequency requirements

📡 Efficient Communication

BLE 5.0 extended advertising and connection-less data transfer

🖥️ E-Paper Display

Bistable displays that retain content without power consumption

Display Specifications:

Size Resolution Colors Typical Use
2.13" 250 x 122 Black/White/Red/Yellow Small items, shelf strips
2.9" 296 x 128 Black/White/Red/Yellow Standard price tags
3.5" 384 x 240 Black/White/Red/Yellow Medium displays, detailed product info
3.7" 480 x 280 Black/White/Red/Yellow Enhanced product displays, promotions
4.2" 400 x 300 Black/White/Red/Yellow Promotional displays
7.5" 800 x 480 Black/White/Red/Yellow Department signs

Message Routing

Understanding how messages flow through the system is crucial for troubleshooting and optimization. Our architecture prioritizes direct connections for WiFi ESLs while using efficient gateway routing for BLE devices.

Routing Paths

Direct Routes (No Gateway Required): ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ Server ←→ WiFi ESL (ESP32-S3) (Direct Internet, Real-time) Server ←→ Main Gateway (ESP32-S3) (Direct Internet, Persistent) Gateway-Routed (BLE Devices): ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ Server → Main Gateway (ESP32-S3) → BLE ESL (nRF52832) Server → Main Gateway (ESP32-S3) → Mesh Gateway (ESP32-C3) → BLE ESL (nRF52832) Broadcast Routes: ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ Server → All WiFi ESLs (Direct broadcast, no gateway) Server → All BLE Devices (Routed through gateways)

Routing Decision Tree

1

Message Received at Server

Check destination device type and connectivity method

2

Is it a WiFi ESL (ESP32-S3)?

Yes → Send directly via Internet (no gateway needed)
No → Continue to step 3

3

BLE ESL (nRF52832) Routing

Lookup device's assigned gateway in routing table

4

Send to Gateway

Route through ESP32-S3 main gateway, then ESP32-C3 mesh if needed

5

Gateway Delivers to BLE ESL

Gateway waits for nRF52832 device wake-up or attempts immediate delivery

Connection Advantages by Type

Device Type Hardware Connection Advantages Use Cases
WiFi ESL ESP32-S3 Series Direct to Server Real-time updates, No gateway dependency, High reliability High-value items, Promotional displays, Critical pricing
BLE ESL nRF52832 Gateway-routed 4+ year battery life, Cost-effective, Mass deployment Standard shelf labels, Large-scale deployments

Scalability Considerations

The architecture supports deployments from 10 to 100,000+ ESL devices

Scaling Guidelines

Deployment Size Architecture Components Considerations
Small
(10-100 ESLs)		 Single Gateway 1 Main Gateway All BLE devices connect directly to main gateway
Medium
(100-1,000 ESLs)		 Basic Mesh 1 Main + 2-5 Mesh Gateways Zone-based deployment, consider WiFi ESLs for critical items
Large
(1,000-10,000 ESLs)		 Full Mesh 1 Main + 10-50 Mesh Gateways Hierarchical zones, load balancing required
Enterprise
(10,000+ ESLs)		 Multi-Site Multiple Main + 50+ Mesh per site Distributed servers, regional failover

Performance Optimization

🚀 Message Batching

Group updates to reduce network overhead

⏱️ Scheduled Updates

Align with ESL wake cycles for efficiency

💾 Edge Caching

Store common data at gateway level

🔄 Load Distribution

Balance devices across gateways