EMS Line Controller DLR PCB 🌡️⚡

Sensor HAT for a solar-powered, cellular-connected RTU — mounts to a transmission tower cross-arm, feeds IEEE 738 calculations via ems-line-controller-dlr

Solar-powered remote terminal unit (RTU) deployed unattended on transmission tower cross-arms. A small solar panel and LiFePO4 battery keep the Pi running indefinitely. A cellular modem (LTE Cat-M1) publishes sensor data and dynamic ratings to the MQTT broker — no site WiFi or wired backhaul required. The unit is designed for 30-year conductor-adjacent deployment with no scheduled maintenance.

65x56mm 4-layer Pi HAT. FLIR Lepton 3.5 (SPI), DHT22 (GPIO), SI1145 (I2C), YL-83 (ADC via ADS1115). 5V from Pi header, 3.3V LDO for analog front-end. Conformal coated, IP55 when potted inside the field enclosure.

System Context

rectangle transmission_tower {
  rectangle field_enclosure {
    rectangle dlr_pcb
    rectangle raspberry_pi
    rectangle cellular_modem
  }
  rectangle solar_panel
  rectangle lifepo4_battery
  rectangle conductor
}

queue mqtt_broker
rectangle line_controller_pst

solar_panel -d- lifepo4_battery: charge
lifepo4_battery -d- raspberry_pi: 5V regulated
conductor -u- dlr_pcb: thermal view\n(FLIR Lepton)
dlr_pcb -d- raspberry_pi: 40-pin HAT connector
raspberry_pi -r- cellular_modem: USB / RS-485
cellular_modem -r- mqtt_broker: LTE Cat-M1
mqtt_broker -r- line_controller_pst: tap adjustment commands

The PCB is the physical sensing layer of the DLR feedback loop. Every measurement it takes flows through the IEEE 738 calculation in ems-line-controller-dlr and ultimately determines whether the phase shift transformer adjusts its tap position.

Board Spec

graph LR
    PI["Pi 5V Rail<br/>40-pin Header"] --> LDO["AP2112K<br/>3.3V 600mA LDO"]
    PI --> FLIR["FLIR Lepton 3.5<br/>SPI0 + GPIO25 VSYNC"]
    PI --> DHT["DHT22<br/>GPIO4 + 10k Pull-up"]
    LDO --> ADC["ADS1115<br/>I2C 0x48"]
    LDO --> UV["SI1145<br/>I2C 0x60"]
    ADC --> RAIN["YL-83<br/>Analog 0-3.3V"]

    style PI fill:#4a9,stroke:#333
    style LDO fill:#a94,stroke:#333
    style FLIR fill:#49a,stroke:#333
    style DHT fill:#94a,stroke:#333
    style ADC fill:#94a,stroke:#333
    style UV fill:#94a,stroke:#333
    style RAIN fill:#669,stroke:#333

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Pinout

flowchart LR
classDef default fill:transparent,stroke:#333
classDef pwr fill:#4a9,stroke:#333,color:#fff
classDef spi fill:#49a,stroke:#333,color:#fff
classDef i2c fill:#94a,stroke:#333,color:#fff
classDef gpio fill:#a94,stroke:#333,color:#fff
classDef adc fill:#669,stroke:#333,color:#fff

subgraph pi_header ["Pi 40-Pin Header"]
  pin1["1 · 3V3"]
  pin2["2 · 5V"]
  pin3["3 · SDA1"]
  pin5["5 · SCL1"]
  pin7["7 · GPIO4"]
  pin19["19 · SPI0_MOSI"]
  pin21["21 · SPI0_MISO"]
  pin22["22 · GPIO25"]
  pin23["23 · SPI0_SCLK"]
  pin24["24 · SPI0_CE0"]
end

subgraph sensors ["Sensors"]
  flir["FLIR Lepton 3.5"]
  dht["DHT22"]
  si["SI1145"]
  ads["ADS1115"]
  yl["YL-83"]
end

pin2 --> flir
pin19 --> flir
pin21 --> flir
pin23 --> flir
pin24 --> flir
pin22 --> flir

pin7 --> dht

pin3 --> si
pin5 --> si

pin3 --> ads
pin5 --> ads
ads --> yl

class pin1,pin2 pwr
class pin19,pin21,pin23,pin24 spi
class pin3,pin5 i2c
class pin7,pin22 gpio
class ads,yl adc
class flir spi
class dht gpio
class si i2c

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Sensor Interfaces

Sensor	Interface	Pi Pins	Sample Rate	Measurement	Feeds IEEE 738 Variable
FLIR Lepton 3.5	SPI0 + VSYNC	19, 21, 23, 24, 22	8.6 Hz (frame)	Conductor surface temp	$R_{thermal}$
DHT22	GPIO4 (1-Wire)	7	0.5 Hz	Ambient temp + humidity	$T_{amb}$
SI1145	I2C (0x60)	3, 5	10 Hz	UV / Visible / IR irradiance	$\Delta T_{solar}$
YL-83 → ADS1115	I2C (0x48) ch0	3, 5	860 SPS	Rain intensity (0–3.3V analog)	$\Delta T_{rain}$

Every sensor reading on this board maps to exactly one term in the IEEE 738 dynamic rating equation:

$$ I_{max} = \sqrt{\frac{q_c + q_r - q_s}{R_{ac}}} $$

Power Budget

Rail	Source	Consumer	Typical	Peak
5V	Pi header pin 2	FLIR Lepton 3.5	150 mA	650 mA (shutter)
5V	Pi header pin 2	DHT22	1.5 mA	2.5 mA
3.3V	AP2112K LDO	ADS1115	0.15 mA	0.2 mA
3.3V	AP2112K LDO	SI1145	3.5 mA	5.5 mA
3.3V	AP2112K LDO	YL-83 comparator	5 mA	8 mA
		Total	160 mA	666 mA

Peak draw is dominated by the Lepton's shutter event (~500ms every 3 minutes). Pi 5V rail supplies up to 1.5A to HATs — 44% headroom at peak.

Environmental

Parameter	Spec	Notes
Operating temp	-40°C to +85°C	Industrial grade components throughout
Conformal coat	Dow Corning 1-2577	Applied post-assembly, mask connectors
Enclosure rating	IP55 (with field enclosure)	Board alone is not rated
Vibration	IEC 60068-2-6 (5–500 Hz, 2g)	Transmission tower wind loading
Expected service life	30 years	Matches conductor replacement cycle
MTBF	>200,000 hours	Derated per MIL-HDBK-217F
Mounting	M2.5 standoffs, Pi HAT spec	58x23mm hole pattern

Fabrication Pipeline

 1. uv run poe notebook         → theory.ipynb: power budget + signal integrity
 2. uv run poe build            → SKiDL netlist + schematic
 3. uv run poe sim              → validate LDO dropout, I2C rise time, SPI timing
 4. /generate-schematic         → professional .kicad_sch

    ┌──────────────────────────────────────────────────────┐
    │  HUMAN: open pcbnew, import netlist, save, close     │
    └──────────────────────────────────────────────────────┘

 5. /layout-pcb                 → place + autoroute + ground pour + DRC

    ┌──────────────────────────────────────────────────────┐
    │  HUMAN: review SVG, adjust pcb_placement.yaml        │
    └──────────────────────────────────────────────────────┘

 6. uv run poe validate-asm     → DRC 0 errors
 7. uv run poe generate-asm     → gerbers + BOM + CPL

Layer Stack

Layer	Use
F.Cu	Signal — SPI, I2C, GPIO
In1.Cu	GND pour (unbroken under FLIR)
In2.Cu	3.3V pour
B.Cu	5V distribution + Pi header

Unbroken ground plane under the Lepton is critical — SPI runs at 20 MHz and the thermal imager is noise-sensitive. Analog traces from YL-83 to ADS1115 are guard-ringed on F.Cu.

Project Structure

├── pyproject.toml              # Dependencies and build config
├── theory.ipynb                # Power budget + signal integrity derivation
├── sim/
│   ├── model.py                # LDO dropout, I2C rise time, SPI timing
│   └── test_run.py             # Assert simulation matches theory
├── cad/
│   ├── netlist/
│   │   ├── model.py            # Top-level SKiDL circuit
│   │   ├── power.py            # 5V rail + AP2112K LDO
│   │   ├── sensors.py          # FLIR, DHT22, SI1145, ADS1115, YL-83
│   │   └── connectors.py       # 40-pin HAT header + sensor headers
│   ├── layout_spec.yaml        # Schematic block layout
│   ├── pcb_placement.yaml      # Component positions
│   └── drawing-sheet.kicad_wks # Title block
├── output/
│   ├── drawings/               # Schematic SVG + PDF
│   ├── gerbers/                # Fabrication files
│   └── fab/                    # BOM + CPL for assembly
└── readme.md                   # This file