// Heltec WiFi LoRa 32 V3 (SX1262) thermostat slave, continuous control

// 7/12/25 Heltec V3 slave thermostat

// Users/graham/Dropbox/electronics/Arduino/lora/heltec_tests/heltec1/slow_updates/heltec_t_command_send_one_DS18B20_temp3/heltec_t_command_send_one_DS18B20_temp3.ino

// - DS18B20 on GPIO7 (inside / control sensor)

// - DS18B20 on GPIO5 (greenhouse)

// - DS18B20 on GPIO4 (outside)

// - Relay on GPIO6 (via transistor + your LED)

// - Device ID prefix: commands must start with DEVICE_ID

//

// Commands:

//

// 1) Set config + read:

// "APPLEtTTHH"

//

// "APPLE" = DEVICE_ID (5 chars)

// 't' = thermostat config command (heating mode)

// TT = setpoint in °C (2 digits, integer)

// HH = hysteresis in °C (2 digits, integer)

//

// Example: APPLEt3002 => setpoint 30C, hysteresis 2C

//

// Behaviour: updates setpoint & hysteresis, reads temps, updates relay,

// replies "IN,GH,OUT,SETPOINT"

//

// 2) Read-only (no config change):

// "APPLEr0000" (or simply "APPLEr")

//

// Behaviour: reads temps, updates relay using existing setpoint/hysteresis,

// replies "IN,GH,OUT,SETPOINT"

//

// OLED:

// - Big top: inside temp + "RL ON"/"RL OFF" at top-right

// - Line2: "GH:xx.x OUT:yy.y"

// - Line3: "SP:xx H:yy"

// - Line4: "RSS:-nn APPLE"

#define HELTEC_POWER_BUTTON // long-press PRG = power control

#include <heltec_unofficial.h>

#include <OneWire.h>

#include <DallasTemperature.h>

#include <math.h>

// ---- Device ID prefix ----

#define DEVICE_ID "APPLE" // 5-character ID for this node

// ---- DS18B20 pins ----

#define PIN_INSIDE 7 // inside / control sensor

#define PIN_GREENHOUSE 5 // greenhouse sensor

#define PIN_OUTSIDE 4 // outside sensor

// ---- Relay on GPIO6 ----

#define RELAY_PIN 6

// ---- OneWire + DallasTemperature instances ----

OneWire oneWireInside(PIN_INSIDE);

OneWire oneWireGH(PIN_GREENHOUSE);

OneWire oneWireOut(PIN_OUTSIDE);

DallasTemperature sensorInside(&oneWireInside);

DallasTemperature sensorGH(&oneWireGH);

DallasTemperature sensorOut(&oneWireOut);

// ---- Temperature variables ----

float tempInsideC = NAN; // control temperature (inside)

float tempGreenhouseC = NAN; // greenhouse

float tempOutsideC = NAN; // outside

// ---- Thermostat settings (initial) ----

float setpointC = 30.0;

float hysteresisC = 2.0;

// LoRa receive

String rxData;

volatile bool rxFlag = false;

// Relay state (true = ON)

bool relayOn = false;

// Periodic temperature update interval

const unsigned long TEMP_INTERVAL_MS = 5000; // 5 seconds

unsigned long lastTempMillis = 0;

// Last radio stats for OLED

float lastRSSI = NAN;

// ISR forward declaration

void onRx();

// ---- Generic DS18B20 read ----

float readTemperature(DallasTemperature &s) {

s.requestTemperatures();

float t = s.getTempCByIndex(0);

if (t == DEVICE_DISCONNECTED_C) {

return NAN;

}

return t;

}

// ---- Read all three sensors ----

void readAllTemperatures() {

tempInsideC = readTemperature(sensorInside);

tempGreenhouseC = readTemperature(sensorGH);

tempOutsideC = readTemperature(sensorOut);

Serial.print("Temps: IN=");

if (isnan(tempInsideC)) Serial.print("NaN"); else Serial.printf("%.2f", tempInsideC);

Serial.print(" GH=");

if (isnan(tempGreenhouseC)) Serial.print("NaN"); else Serial.printf("%.2f", tempGreenhouseC);

Serial.print(" OUT=");

if (isnan(tempOutsideC)) Serial.print("NaN"); else Serial.printf("%.2f", tempOutsideC);

Serial.println();

}

// ---- Apply thermostat logic (heating mode, using inside temp) ----

void updateThermostat(float insideC) {

if (isnan(insideC)) {

// Sensor error -> turn relay OFF for safety

relayOn = false;

} else {

float onThreshold = setpointC - hysteresisC;

float offThreshold = setpointC;

// Heating mode with hysteresis

if (!relayOn && insideC <= onThreshold) {

relayOn = true;

} else if (relayOn && insideC >= offThreshold) {

relayOn = false;

}

}

digitalWrite(RELAY_PIN, relayOn ? HIGH : LOW);

Serial.printf("Thermostat: set=%.1fC, hyst=%.1fC, IN=%.2fC, relay=%s\n",

setpointC, hysteresisC,

isnan(insideC) ? -999.0 : insideC,

relayOn ? "ON" : "OFF");

}

// ---- Build and send reply: IN,GH,OUT,SETPOINT ----

/*

void sendTemperatureReply() {

// Build reply: IN,GH,OUT,SETPOINT

char replyMsg[64];

snprintf(replyMsg, sizeof(replyMsg),

"%.2f,%.2f,%.2f,%.2f",

tempInsideC, tempGreenhouseC, tempOutsideC, setpointC);

Serial.printf("Replying with: %s\n", replyMsg);

radio.clearDio1Action();

heltec_led(50);

RADIOLIB(radio.transmit(replyMsg));

Serial.printf("[RadioLib] radio.transmit(replyMsg) returned %d\n", _radiolib_status);

heltec_led(0);

radio.setDio1Action(onRx);

RADIOLIB_OR_HALT(radio.startReceive(RADIOLIB_SX126X_RX_TIMEOUT_INF));

}

*/

void sendTemperatureReply() {

char replyMsg[96];

snprintf(replyMsg, sizeof(replyMsg),

"%s,%.2f,%.2f,%.2f,%.2f",

DEVICE_ID, tempInsideC, tempGreenhouseC, tempOutsideC, setpointC);

Serial.printf("Replying with: %s\n", replyMsg);

radio.clearDio1Action();

heltec_led(50);

RADIOLIB(radio.transmit(replyMsg));

Serial.printf("[RadioLib] radio.transmit(replyMsg) returned %d\n", _radiolib_status);

heltec_led(0);

radio.setDio1Action(onRx);

RADIOLIB_OR_HALT(radio.startReceive(RADIOLIB_SX126X_RX_TIMEOUT_INF));

}

// ---- OLED UI ----

void updateDisplay() {

display.clear();

// Big inside temperature at top (left)

display.setTextAlignment(TEXT_ALIGN_LEFT);

display.setFont(ArialMT_Plain_24);

String tempStr;

if (isnan(tempInsideC)) {

tempStr = "--.-C";

} else {

tempStr = String(tempInsideC, 1) + "C";

}

display.drawString(0, 0, tempStr);

// Small "RL ON/OFF" at top-right

display.setFont(ArialMT_Plain_10);

display.setTextAlignment(TEXT_ALIGN_RIGHT);

String rlStr = relayOn ? "RL ON" : "RL OFF";

display.drawString(127, 4, rlStr);

display.setTextAlignment(TEXT_ALIGN_LEFT);

// Line 2: greenhouse + outside, e.g. "GH:23.8 OUT:12.3"

String line2 = "GH:";

if (isnan(tempGreenhouseC)) line2 += "--.-";

else line2 += String(tempGreenhouseC, 1);

line2 += " OUT:";

if (isnan(tempOutsideC)) line2 += "--.-";

else line2 += String(tempOutsideC, 1);

display.drawString(0, 28, line2);

// Line 3: setpoint + hysteresis

int spInt = (int)round(setpointC);

int hyInt = (int)round(hysteresisC);

String line3 = "SP:" + String(spInt) + " H:" + String(hyInt);

display.drawString(0, 40, line3);

// Line 4: RSSI + device name, e.g. "RSS:-34 APPLE"

String line4 = "RSS:";

if (isnan(lastRSSI)) line4 += "--";

else line4 += String((int)lastRSSI);

line4 += " ";

line4 += DEVICE_ID;

display.drawString(0, 52, line4);

display.display();

}

// -------------------------------------------------------------------

// SETUP

// -------------------------------------------------------------------

void setup() {

heltec_setup(); // sets up Serial, display, radio, button, etc.

Serial.println("Heltec V3 LoRa thermostat SLAVE (3 sensors, ID-only commands)");

Serial.println("Initialising radio and DS18B20s...");

// Start DS18B20 sensors

sensorInside.begin();

sensorGH.begin();

sensorOut.begin();

// Relay pin

pinMode(RELAY_PIN, OUTPUT);

digitalWrite(RELAY_PIN, LOW);

relayOn = false;

// Basic radio init

RADIOLIB_OR_HALT(radio.begin());

// Disable CRC to match SX1278 master

RADIOLIB_OR_HALT(radio.setCRC(0));

// Match SX1278 master settings

RADIOLIB_OR_HALT(radio.setFrequency(868.0));

RADIOLIB_OR_HALT(radio.setBandwidth(125.0));

RADIOLIB_OR_HALT(radio.setSpreadingFactor(9));

RADIOLIB_OR_HALT(radio.setCodingRate(5)); // 4/5

RADIOLIB_OR_HALT(radio.setPreambleLength(8));

RADIOLIB_OR_HALT(radio.setSyncWord(0x34));

RADIOLIB_OR_HALT(radio.setOutputPower(17));

// Set callback on DIO1 for received packets and start RX

radio.setDio1Action(onRx);

RADIOLIB_OR_HALT(radio.startReceive(RADIOLIB_SX126X_RX_TIMEOUT_INF));

Serial.println("Commands:");

Serial.println(" " DEVICE_ID "tTTHH -> set setpoint/hyst, reply IN,GH,OUT,SET");

Serial.println(" " DEVICE_ID "r0000 -> read-only, reply IN,GH,OUT,SET");

Serial.println("Example: " DEVICE_ID "t3002 (30C, hyst 2C)");

Serial.printf("Initial setpoint = %.1f C, hysteresis = %.1f C\n",

setpointC, hysteresisC);

// Initial temperature read + thermostat decision

readAllTemperatures();

updateThermostat(tempInsideC);

lastTempMillis = millis();

updateDisplay();

}

// -------------------------------------------------------------------

// LOOP

// -------------------------------------------------------------------

void loop() {

heltec_loop(); // keep Heltec power button etc working

unsigned long now = millis();

// Periodic background temperature check and thermostat control

if (now - lastTempMillis >= TEMP_INTERVAL_MS) {

lastTempMillis = now;

readAllTemperatures();

updateThermostat(tempInsideC);

updateDisplay();

}

// Handle received LoRa packets

if (rxFlag) {

rxFlag = false;

// Read received data

radio.readData(rxData);

if (_radiolib_status == RADIOLIB_ERR_NONE) {

rxData.trim();

Serial.printf("RX: \"%s\"\n", rxData.c_str());

float rssi = radio.getRSSI();

float snr = radio.getSNR();

Serial.printf(" RSSI: %.2f dBm\n", rssi);

Serial.printf(" SNR: %.2f dB\n", snr);

lastRSSI = rssi;

// Expect at least "APPLEx" = 6 chars

if (rxData.length() >= 6) {

String prefix = rxData.substring(0, 5);

char cmdType = rxData.charAt(5);

if (prefix == DEVICE_ID) {

// 1) Config command: DEVICE_ID + 't' + TTHH (>= 10 chars)

if (cmdType == 't') {

if (rxData.length() >= 10) {

String setStr = rxData.substring(6, 8); // TT

String hystStr = rxData.substring(8, 10); // HH

int setInt = setStr.toInt();

int hystInt = hystStr.toInt();

// Simple sanity limits

if (setInt >= -40 && setInt <= 99 && hystInt >= 0 && hystInt <= 50) {

setpointC = (float)setInt;

hysteresisC = (float)hystInt;

Serial.printf("New config: set=%.1fC, hyst=%.1fC\n",

setpointC, hysteresisC);

// Read all temps, update thermostat, reply

readAllTemperatures();

updateThermostat(tempInsideC);

updateDisplay();

sendTemperatureReply();

} else {

Serial.println("Out-of-range setpoint/hysteresis, ignoring.");

}

} else {

Serial.println("Thermostat command too short, ignoring.");

}

}

// 2) Read-only command: DEVICE_ID + 'r' (with or without extra digits)

else if (cmdType == 'r') {

Serial.println("Read-only command: no config change.");

// Just read temps, apply thermostat with existing setpoint/hyst, reply

readAllTemperatures();

updateThermostat(tempInsideC);

updateDisplay();

sendTemperatureReply();

}

else {

Serial.println("Unknown command type for this device, ignoring.");

}

} else {

Serial.println("Prefix does not match this device, ignoring.");

}

} else {

Serial.println("Received too-short packet, ignoring.");

}

// Resume listening

RADIOLIB_OR_HALT(radio.startReceive(RADIOLIB_SX126X_RX_TIMEOUT_INF));

} else {

Serial.printf("RX error (%d), restarting RX\n", _radiolib_status);

RADIOLIB_OR_HALT(radio.startReceive(RADIOLIB_SX126X_RX_TIMEOUT_INF));

}

}

}

// ---- ISR – keep it very short: just set a flag ----

void onRx() {

rxFlag = true;

}