EMS Line Controller PST ⚡🔄

Embedded transformer tap control using Embassy-rs async runtime

Pre-requisites

• rust 1.93+
• ESP32-C3 development board
• 4-channel relay module

Hardware

Component	Purpose	Interface
ESP32-C3	Microcontroller	WiFi/MQTT
4-Channel Relay	Tap switching	GPIO
Multi-tap Transformer	Voltage adjustment	AC

Pinout

flowchart LR
classDef default fill:transparent,stroke:#333

subgraph esp32_c3
  gpio2
  gpio3
  gpio4
  gpio5
  wifi
end

subgraph 4_channel_relay
  relay1
  relay2
  relay3
  relay4
end

subgraph multi_tap_xfmr
  tap1
  tap2
  tap3
  tap4
  primary
  secondary
end

gpio2 --> relay1
gpio3 --> relay2
gpio4 --> relay3
gpio5 --> relay4

relay1 --> tap1
relay2 --> tap2
relay3 --> tap3
relay4 --> tap4

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MQTT Topics

Subscribed:

• sites/{site_id}/devices/dlr_sensor/calculations/amps/{dynamic_rating}

Published:

• sites/{site_id}/devices/pst/measurements/volts/{output_voltage}
• sites/{site_id}/devices/pst/status/{tap_position}

Project Structure

├── Cargo.toml               # Dependencies and build config
├── src/
│   ├── main.rs              # Application entry point
│   ├── app.rs               # Main application logic (exported for testing)
│   ├── mqtt_client.rs       # MQTT subscriber/publisher
│   ├── mqtt_client_test.rs  # MQTT client tests
├── relay_control/
│   ├── relay_control_client_test.rs
│   ├── relay_control_client.rs
│   ├── relay_control_driver.rs
│   └── mod.rs
├── transformer/
│   ├── transformer_client_test.rs
│   ├── transformer_client.rs
│   ├── transformer_driver.rs
│   └── mod.rs

│   └── config.rs            # WiFi and MQTT configuration
├── tests/
│   └── integration.rs       # Hardware integration tests (imports app.rs)
├── .cargo/
│   └── config.toml          # ESP32 build configuration
└── README.md                # This file

Testing Strategy

1. Unit Tests: Colocated *_test.rs files test individual modules
2. Integration Tests: integration.rs imports main function from app.rs for end-to-end testing
3. Embassy-rs: Async runtime enables concurrent MQTT and GPIO operations

Usage

# Install probe-rs
cargo install probe-rs-tools

# Build and flash
cargo run --release

# Debug with probe-rs
probe-rs run --chip esp32c3

# Monitor serial output
probe-rs attach --chip esp32c3

Tap Control Logic

The transformer adjusts tap position based on dynamic rating:

• Higher rating → Lower tap (higher voltage)
• Lower rating → Higher tap (lower voltage)
• Gradual adjustments to prevent voltage spikes