Add serial rotary encoder and api endpoint

src/pqnstack/app/api/main.py

@@ -3,10 +3,12 @@
 from pqnstack.app.api.routes import chsh
 from pqnstack.app.api.routes import qkd
 from pqnstack.app.api.routes import rng
+from pqnstack.app.api.routes import serial
 from pqnstack.app.api.routes import timetagger
 
 api_router = APIRouter()
 api_router.include_router(chsh.router)
 api_router.include_router(qkd.router)
 api_router.include_router(timetagger.router)
 api_router.include_router(rng.router)
+api_router.include_router(serial.router)

src/pqnstack/app/api/routes/serial.py

@@ -0,0 +1,28 @@
+import logging
+from typing import Annotated
+
+from fastapi import APIRouter
+from fastapi import Depends
+from pydantic import BaseModel
+
+from pqnstack.app.core.config import settings
+from pqnstack.pqn.drivers.rotaryencoder import SerialRotaryEncoder
+
+logger = logging.getLogger(__name__)
+router = APIRouter(prefix="/serial", tags=["measure"])
+
+
+def get_rotary_encoder() -> SerialRotaryEncoder:
+    return settings.rotary_encoder
+
+
+SERDep = Annotated[SerialRotaryEncoder, Depends(get_rotary_encoder)]
+
+
+class AngleResponse(BaseModel):
+    theta: float
+
+
+@router.get("/")
+async def read_angle(rotary_encoder: SERDep) -> AngleResponse:
+    return AngleResponse(theta=rotary_encoder.read())

src/pqnstack/app/core/config.py

@@ -10,6 +10,7 @@
 
 from pqnstack.constants import BellState
 from pqnstack.constants import QKDEncodingBasis
+from pqnstack.pqn.drivers.rotaryencoder import SerialRotaryEncoder
 from pqnstack.pqn.protocols.measurement import MeasurementConfig
 
 logger = logging.getLogger(__name__)
@@ -39,6 +40,10 @@ class Settings(BaseSettings):
     bell_state: BellState = BellState.Phi_plus
     timetagger: tuple[str, str] | None = None  # Name of the timetagger to use for the CHSH experiment.
 
+    rotary_encoder: SerialRotaryEncoder = SerialRotaryEncoder(
+        label="rotary_encoder", address="/dev/ttyACM0", offset_degrees=0.0
+    )
+
     model_config = SettingsConfigDict(toml_file="./config.toml", env_file=".env", env_file_encoding="utf-8")
 
     @classmethod

src/pqnstack/pqn/drivers/rotaryencoder.py

@@ -0,0 +1,30 @@
+import atexit
+from dataclasses import dataclass
+from dataclasses import field
+
+import serial
+
+
+@dataclass(slots=True)
+class SerialRotaryEncoder:
+    label: str
+    address: str
+    offset_degrees: float = 0.0
+    _conn: serial.Serial = field(init=False, repr=False)
+
+    def __post_init__(self) -> None:
+        self._conn = serial.Serial(self.address, baudrate=115200, timeout=1)
+        self._conn.write(b"open_channel")
+        self._conn.read(100)
+        self._conn.write(b"ready")
+        self._conn.read(100)
+
+        atexit.register(self.close)
+
+    def close(self) -> None:
+        self._conn.close()
+
+    def read(self) -> float:
+        self._conn.write(b"ANGLE?\n")
+        angle = self._conn.readline().decode().strip()
+        return float(angle) + self.offset_degrees