diff --git a/nl43_dod_poll.py b/nl43_dod_poll.py
new file mode 100644
index 0000000..3691c2e
--- /dev/null
+++ b/nl43_dod_poll.py
@@ -0,0 +1,100 @@
+#!/usr/bin/env python3
+"""
+Diagnostic poller for NL-43 TCP connectivity.
+
+Every interval, open a TCP connection, send DOD?, read response, and log results.
+"""
+
+from __future__ import annotations
+
+import datetime as dt
+import socket
+import time
+from pathlib import Path
+
+# ---- Configuration (edit as needed) ----
+HOST = "192.168.0.10"
+PORT = 2255
+INTERVAL_SECONDS = 5 * 60
+CONNECT_TIMEOUT_SECONDS = 5.0
+READ_TIMEOUT_SECONDS = 5.0
+LOG_PATH = Path("nl43_dod_poll.log")
+# ---------------------------------------
+
+
+def _timestamp() -> str:
+    return dt.datetime.utcnow().isoformat(timespec="seconds") + "Z"
+
+
+def _read_line(sock_file) -> str:
+    line = sock_file.readline()
+    if not line:
+        raise ConnectionError("Socket closed before full response")
+    return line.decode("ascii", errors="ignore").strip()
+
+
+def _poll_once() -> tuple[bool, str, str, str, str]:
+    sock = None
+    result_code = ""
+    data_line = ""
+    try:
+        sock = socket.create_connection((HOST, PORT), timeout=CONNECT_TIMEOUT_SECONDS)
+        sock.settimeout(READ_TIMEOUT_SECONDS)
+
+        sock.sendall(b"DOD?\r\n")
+
+        with sock.makefile("rb") as sock_file:
+            result_code = _read_line(sock_file)
+            if result_code.startswith("$"):
+                result_code = result_code[1:].strip()
+
+            if result_code != "R+0000":
+                return False, "other", f"device_result={result_code}", result_code, data_line
+
+            data_line = _read_line(sock_file)
+            if data_line.startswith("$"):
+                data_line = data_line[1:].strip()
+
+        return True, "none", "ok", result_code, data_line
+    except socket.timeout:
+        return False, "timeout", "socket_timeout", result_code, data_line
+    except ConnectionRefusedError:
+        return False, "refused", "connection_refused", result_code, data_line
+    except OSError as exc:
+        return False, "other", f"os_error={exc.__class__.__name__}", result_code, data_line
+    except Exception as exc:
+        return False, "other", f"error={exc.__class__.__name__}", result_code, data_line
+    finally:
+        if sock is not None:
+            try:
+                sock.shutdown(socket.SHUT_RDWR)
+            except OSError:
+                pass
+            sock.close()
+
+
+def _log_line(text: str) -> None:
+    print(text, flush=True)
+    with LOG_PATH.open("a", encoding="ascii") as handle:
+        handle.write(text + "\n")
+
+
+def main() -> None:
+    while True:
+        start = time.monotonic()
+        ok, error_type, detail, result_code, data_line = _poll_once()
+
+        status = "success" if ok else "failure"
+        msg = (
+            f"ts={_timestamp()} status={status} error_type={error_type} "
+            f"detail={detail} result_code={result_code} data={data_line}"
+        )
+        _log_line(msg)
+
+        elapsed = time.monotonic() - start
+        sleep_for = max(0.0, INTERVAL_SECONDS - elapsed)
+        time.sleep(sleep_for)
+
+
+if __name__ == "__main__":
+    main()