Initial project: XIAO ESP32S3 + SX1262 LoRa sensor link hytte–hjem

- cabin_node: subscribes to local MQTT (ESPHome sensors), sends
  temperature, battery voltage/SOC and switch states over LoRa SF12
- cabin_gw: receives LoRa packets, publishes JSON to home MQTT broker
- Bidirectional: gateway forwards ON/OFF commands from home HA to node
- cabin_node always in RX mode (12V powered) — commands arrive instantly
- ESPHome config for ESP32 on teknisk rom: Victron MPPT BLE + JBD BMS
  BLE + DS18B20 temperatures + GPIO switches for varme/VVB

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

include/config.h

@@ -0,0 +1,62 @@
+#pragma once
+
+// LoRa radio parameters — must match exactly on node and gateway
+#define LORA_FREQ      868.0   // MHz
+#define LORA_SF        12
+#define LORA_BW        125.0   // kHz
+#define LORA_CR        5
+#define LORA_SYNC_WORD 0xAB    // distinct from ice-track (0x34)
+#define LORA_POWER     22      // dBm (SX1262 max)
+
+// Wio-SX1262 pins for XIAO ESP32S3
+// Verify against https://wiki.seeedstudio.com/wio_sx1262_with_xiao_esp32s3
+#define LORA_NSS       44   // D7
+#define LORA_RST       43   // D6
+#define LORA_DIO1       2   // D1
+#define LORA_BUSY       1   // D0
+
+// Send interval (node) — 30 min fills one packet; adjust 1–4x/hour
+#define SEND_INTERVAL_MS (30UL * 60UL * 1000UL)
+
+// MQTT broker (home, shared with mitt_lora)
+#define MQTT_HOST "192.168.86.31"
+#define MQTT_PORT 1883
+#define MQTT_USER "mqtt"
+#ifndef MQTT_PASS
+#define MQTT_PASS ""
+#endif
+
+// MQTT topics (cabin ESPHome → node subscribes to these)
+#define TOPIC_TEMP_IN   "hytte/sensor/temp_inne"
+#define TOPIC_TEMP_OUT  "hytte/sensor/temp_ute"
+#define TOPIC_BATT_MV   "hytte/sensor/batt_mv"
+#define TOPIC_BATT_PCT  "hytte/sensor/batt_pct"
+
+// MQTT topic gateway publishes received packets to (home broker)
+#define TOPIC_GW_STATUS "hytte/lora/status"
+
+// Command topics (home HA publishes → cabin_gw → LoRa → cabin_node → ESPHome)
+// Payload: "ON" or "OFF"
+#define TOPIC_CMD_VARME  "hytte/cmd/varme"
+#define TOPIC_CMD_VVB    "hytte/cmd/vvb"
+
+// ESPHome publishes switch states here (cabin_node subscribes)
+#define TOPIC_STATE_VARME "hytte/switch/varme/state"
+#define TOPIC_STATE_VVB   "hytte/switch/vvb/state"
+
+// WiFi credentials
+#ifndef WIFI_SSID
+#define WIFI_SSID "your-ssid"
+#endif
+#ifndef WIFI_PASS
+#define WIFI_PASS "your-pass"
+#endif
+
+// HMAC key — 32+ chars, keep secret
+#ifndef HMAC_KEY
+#define HMAC_KEY "hytte-link-hmac-key-replace-me"
+#endif
+
+#if __has_include("secrets.h")
+#include "secrets.h"
+#endif

include/crypto.h

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+#pragma once
+#include <stdint.h>
+#include <stddef.h>
+#include <string.h>
+#include "mbedtls/md.h"
+#include "config.h"
+
+// Returns a 4-byte truncated HMAC-SHA256 over `data` of `len` bytes.
+inline uint32_t hmac_sig(const uint8_t *data, size_t len)
+{
+  static const char *key = HMAC_KEY;
+  uint8_t out[32];
+  mbedtls_md_hmac(
+    mbedtls_md_info_from_type(MBEDTLS_MD_SHA256),
+    reinterpret_cast<const uint8_t *>(key), strlen(key),
+    data, len, out);
+  uint32_t sig;
+  memcpy(&sig, out, 4);
+  return sig;
+}

include/packets.h

@@ -0,0 +1,36 @@
+#pragma once
+#include <stdint.h>
+
+#define CABIN_PACKET_MAGIC 0xCA
+#define CABIN_CMD_MAGIC    0xCB
+
+// Command IDs
+#define CMD_VARME   0x01
+#define CMD_VVB     0x02   // varmtvannsbereder
+
+// Wire format: 13 bytes total
+// At SF12 BW125: ~1.3s airtime
+// flags bits: 0=varme, 1=vvb (1=on, 0=off)
+#define CABIN_FLAG_VARME  (1 << 0)
+#define CABIN_FLAG_VVB    (1 << 1)
+
+struct __attribute__((packed)) CabinPacket {
+  uint8_t  magic;         // = CABIN_PACKET_MAGIC
+  uint8_t  seq;           // rolling counter
+  int16_t  temp_in_x10;   // indoor temp * 10  (213 = 21.3 °C), INT16_MIN = no data
+  int16_t  temp_out_x10;  // outdoor temp * 10, INT16_MIN = no data
+  uint16_t batt_mv;       // battery voltage mV (12V system: ~10000–14400)
+  uint8_t  batt_pct;      // SOC 0–100, 0xFF = no data
+  uint8_t  flags;         // switch states: bit0=varme, bit1=vvb
+  uint32_t sig;           // truncated HMAC-SHA256
+};
+
+// Command packet: home → gateway → node → ESPHome switch
+// 8 bytes total
+struct __attribute__((packed)) CabinCmdPacket {
+  uint8_t  magic;   // = CABIN_CMD_MAGIC
+  uint8_t  seq;
+  uint8_t  cmd_id;  // CMD_VARME, CMD_VVB, ...
+  uint8_t  value;   // 0 = off, 1 = on
+  uint32_t sig;
+};

include/secrets.example.h

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+#pragma once
+
+// Copy to secrets.h and fill in before building
+#define WIFI_SSID  "your-wifi-ssid"
+#define WIFI_PASS  "your-wifi-password"
+#define MQTT_PASS  "your-mqtt-password"
+#define HMAC_KEY   "your-secret-hmac-key-at-least-32-chars"