feat(sensors): add 1-Wire (Dallas) temperature sensor support

Add a portable 1-Wire bus driver to EnvironmentSensorManager covering
the DallasTemperature-supported temperature families (DS18B20, DS18S20,
DS1822, DS1825/MAX31850, DS28EA00). Each detected probe on the bus is
registered as its own telemetry sub-channel, so multiple probes on one
pin work without configuration.

The driver gates on a 1-Wire presence pulse before engaging
DallasTemperature, mirroring the I2C ACK check, so an absent bus pushes
no telemetry entries. Boards opt in purely via build flags
(ENV_INCLUDE_ONEWIRE + TELEM_ONEWIRE_PIN) with no source changes; the
RAK4631 sensor env enables it on WB_IO1.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

platformio.ini

@@ -152,6 +152,8 @@ lib_deps =
   stevemarple/MicroNMEA @ ^2.0.6
   adafruit/Adafruit BME680 Library @ ^2.0.4
   adafruit/Adafruit BMP085 Library @ ^1.2.4
+  paulstoffregen/OneWire @ ^2.3.8
+  milesburton/DallasTemperature @ ^3.11.0
 
 ; ----------------- TESTING ---------------------
 

src/helpers/sensors/EnvironmentSensorManager.cpp

@@ -160,6 +160,14 @@ static Adafruit_VL53L0X VL53L0X;
 static RAK12035_SoilMoisture RAK12035;
 #endif
 
+#if ENV_INCLUDE_ONEWIRE
+#ifndef TELEM_ONEWIRE_PIN
+#error "ENV_INCLUDE_ONEWIRE requires TELEM_ONEWIRE_PIN to be defined in the board's build_flags"
+#endif
+#include "OneWireSensor.h"
+static OneWireSensor ONEWIRE(TELEM_ONEWIRE_PIN);
+#endif
+
 #if ENV_INCLUDE_GPS && defined(RAK_BOARD) && !defined(RAK_WISMESH_TAG)
 #define RAK_WISBLOCK_GPS
 #endif
@@ -475,6 +483,16 @@ static void query_rak12035(uint8_t ch, uint8_t sub_ch, CayenneLPP& lpp) {
 }
 #endif
 
+#if ENV_INCLUDE_ONEWIRE
+// 1-Wire has no I2C address and no init(wire, addr) entry — its
+// presence-pulse probe and bus enumeration both live in
+// OneWireSensor::begin(), called from the dedicated registration
+// pass in EnvironmentSensorManager::begin().
+static void query_onewire(uint8_t ch, uint8_t sub_ch, CayenneLPP& lpp) {
+  ONEWIRE.query(ch, sub_ch, lpp);
+}
+#endif
+
 #if ENV_INCLUDE_BME680_BSEC
 static void bsec_load_state() {
   using namespace Adafruit_LittleFS_Namespace;
@@ -655,6 +673,34 @@ bool EnvironmentSensorManager::begin() {
     }
   }
 
+  // ----------------------------------------------------------
+  // 1-Wire bus registration pass.
+  //
+  // Portability: any board enables 1-Wire by adding
+  //   -D ENV_INCLUDE_ONEWIRE=1
+  //   -D TELEM_ONEWIRE_PIN=<gpio>
+  // to its variant's build_flags. No source changes required.
+  //
+  // OneWireSensor::begin() issues a 1-Wire reset and checks for a
+  // presence pulse before touching DallasTemperature, mirroring the
+  // I2C ACK gate above. With no probe attached, it returns 0 and no
+  // entries are pushed — the same "never touch absent hardware"
+  // invariant applies here as on the I2C bus.
+  // ----------------------------------------------------------
+  #if ENV_INCLUDE_ONEWIRE
+  {
+    uint8_t found = ONEWIRE.begin();
+    if (found == 0) {
+      MESH_DEBUG_PRINTLN("1-Wire not detected on pin %d", (int)TELEM_ONEWIRE_PIN);
+    } else {
+      MESH_DEBUG_PRINTLN("Found %u 1-Wire temperature device(s) on pin %d", (unsigned)found, (int)TELEM_ONEWIRE_PIN);
+      for (uint8_t sub = 0; sub < found && _active_sensor_count < MAX_ACTIVE_SENSORS; sub++) {
+        _active_sensors[_active_sensor_count++] = { query_onewire, sub };
+      }
+    }
+  }
+  #endif
+
   return true;
 }
 

src/helpers/sensors/OneWireSensor.cpp

@@ -0,0 +1,68 @@
+#include "OneWireSensor.h"
+
+#if ENV_INCLUDE_ONEWIRE
+
+// 1-Wire ROM family codes for the temperature devices the
+// DallasTemperature library knows how to decode. Centralised here so
+// the family filter in begin() reads as a list of supported parts.
+static inline bool is_temperature_family(uint8_t family) {
+  switch (family) {
+    case 0x10: // DS18S20 / DS1820
+    case 0x22: // DS1822
+    case 0x28: // DS18B20
+    case 0x3B: // DS1825 / MAX31850
+    case 0x42: // DS28EA00
+      return true;
+    default:
+      return false;
+  }
+}
+
+OneWireSensor::OneWireSensor(uint8_t pin)
+  : _bus(pin), _dallas(&_bus) {}
+
+uint8_t OneWireSensor::begin() {
+  // Presence-pulse gate. OneWire::reset() returns 1 only when at
+  // least one device on the bus pulls the line low in response to
+  // the reset pulse. Without it, we skip DallasTemperature entirely.
+  if (_bus.reset() != 1) return 0;
+
+  _dallas.begin();
+
+  const uint8_t bus_total = _dallas.getDeviceCount();
+  _count = 0;
+  for (uint8_t i = 0; i < bus_total && _count < MAX_DEVICES; i++) {
+    DeviceAddress addr;
+    if (!_dallas.getAddress(addr, i)) continue;
+
+    // Extension point: a future non-temperature family (e.g. DS2438
+    // battery monitor, family 0x26) would dispatch on this family
+    // byte to its own driver and register a different query_* free
+    // function from the manager. The presence-pulse gate above and
+    // the per-device address storage below are family-agnostic and
+    // can be reused as-is.
+    if (!is_temperature_family(addr[0])) continue;
+
+    memcpy(_addresses[_count], addr, sizeof(DeviceAddress));
+    _count++;
+  }
+
+  return _count;
+}
+
+void OneWireSensor::query(uint8_t channel, uint8_t index, CayenneLPP& lpp) {
+  if (index >= _count) return;
+
+  // Per-device blocking conversion keeps query() stateless and
+  // independent of call order — the cost is one conversion window
+  // (~750 ms at default 12-bit resolution) per device per cycle,
+  // which matches the synchronous read pattern used by the other
+  // sensors in EnvironmentSensorManager.
+  _dallas.requestTemperaturesByAddress(_addresses[index]);
+  const float t = _dallas.getTempC(_addresses[index]);
+  if (t == DEVICE_DISCONNECTED_C) return;
+
+  lpp.addTemperature(channel, t);
+}
+
+#endif // ENV_INCLUDE_ONEWIRE

src/helpers/sensors/OneWireSensor.h

@@ -0,0 +1,50 @@
+#pragma once
+
+// Standalone 1-Wire bus driver for EnvironmentSensorManager.
+//
+// Covers every DallasTemperature-supported temperature family on one
+// bus pin: DS18B20 (0x28), DS18S20 (0x10), DS1822 (0x22), DS1825 /
+// MAX31850 (0x3B), DS28EA00 (0x42). Each detected device is exposed
+// as its own telemetry sub-channel, so an air-and-water deployment
+// with two probes on the same pin "just works".
+//
+// Portability contract: this file contains no board-specific pins or
+// #ifdefs. The bus pin comes from the per-board build flag
+// TELEM_ONEWIRE_PIN, and the whole module is compiled out when
+// ENV_INCLUDE_ONEWIRE is not set.
+
+#if ENV_INCLUDE_ONEWIRE
+
+#include <Arduino.h>
+#include <CayenneLPP.h>
+#include <OneWire.h>
+#include <DallasTemperature.h>
+
+class OneWireSensor {
+public:
+  // Upper bound on devices enumerated from a single bus. Kept under
+  // EnvironmentSensorManager::MAX_ACTIVE_SENSORS so a fully populated
+  // bus cannot overflow the active-sensor table on its own.
+  static const uint8_t MAX_DEVICES = 8;
+
+  explicit OneWireSensor(uint8_t pin);
+
+  // Probes the bus for a 1-Wire presence pulse — the direct analog of
+  // the I2C ACK check the manager's address scan relies on. With no
+  // pulse, returns 0 and DallasTemperature is never engaged; this
+  // preserves the manager's "never touch absent hardware" invariant.
+  // Otherwise enumerates the bus and returns the number of detected
+  // temperature-family devices (clamped to MAX_DEVICES).
+  uint8_t begin();
+
+  // Reads device `index` and writes one temperature channel.
+  void query(uint8_t channel, uint8_t index, CayenneLPP& lpp);
+
+private:
+  OneWire           _bus;
+  DallasTemperature _dallas;
+  uint8_t           _count = 0;
+  DeviceAddress     _addresses[MAX_DEVICES];
+};
+
+#endif // ENV_INCLUDE_ONEWIRE

variants/rak4631/platformio.ini

@@ -186,6 +186,8 @@ build_flags =
   -D ADVERT_LAT=0.0
   -D ADVERT_LON=0.0
   -D ADMIN_PASSWORD='"password"'
+  -D ENV_INCLUDE_ONEWIRE=1
+  -D TELEM_ONEWIRE_PIN=WB_IO1
 ;  -D MESH_PACKET_LOGGING=1
   -D MESH_DEBUG=1
 build_src_filter = ${rak4631.build_src_filter}