Home IoT Hub Series · 09

[Part 9] Did I leave the gas stove on? Burner-temperature safety node

Detect gas stove usage by measuring burner-side heat with a thermocouple.

This part detects gas-stove usage by measuring heat around the burner with a thermocouple module. It does not control gas; it only reports whether heat is present.

Keep the electronics away from direct flame and high heat. The thermocouple tip can be near the hot area, but the Wemos and MAX6675 module should stay protected.

Parts and cost

Pin wiring

Full code

#include <ESP8266WiFi.h>
#include <ESP8266HTTPClient.h>
#include <max6675.h>

const char* ssid     = "IoT_Hub_Net";
const char* password = "iothub1234";
const char* hubURL   = "http://192.168.1.1";

#define SCK  14   // D5
#define CS   12   // D6
#define SO   13   // D7
#define SLOT_NO   6
#define THRESHOLD 50 // 50℃ note= note
#define INTERVAL  5000

MAX6675 thermo(SCK, CS, SO);

void setup() {
  Serial.begin(115200);
  WiFi.mode(WIFI_STA);
  WiFi.begin(ssid, password);
  Serial.print("Connecting to IoT_Hub_Net");
  while (WiFi.status() != WL_CONNECTED) { delay(500); Serial.print("."); }
  Serial.println("\nConnected!");
}

void loop() {
  float temp = thermo.readCelsius();
  if (isnan(temp)) { Serial.println("Read error"); delay(2000); return; }

  int inUse = (temp > THRESHOLD) ? 1 : 0;
  Serial.print("Stove: "); Serial.print(temp);
  Serial.print(" C -> "); Serial.println(inUse ? "ON" : "OFF");

  WiFiClient client; HTTPClient http;
  String url = String(hubURL) + "/set?no"
             + String(SLOT_NO) + "=" + String(inUse);
  http.begin(client, url); http.GET(); http.end();
  Serial.println("HTTP -> " + url);

  delay(INTERVAL);
}

Upload and check

Connect the Wemos D1 Mini to the PC with a USB data cable, select the ESP8266 board and port in the Arduino IDE, upload the sketch, then open Tools → Serial Monitor and set the baud rate to 115200.

Serial Monitor

After uploading, open Tools → Serial Monitor in the Arduino IDE and set the baud rate to 115200. The following is an example Serial Monitor flow for checking normal operation. This is not a real screenshot. It is an example output for checking MAX6675 readings and slot 6 updates.

[BOOT] Home IoT Node #09 - Gas stove thermocouple
[SPI] MAX6675 ready, sample_avg=3
[SENSOR] burner_temp=36.4C
[STATE] stove=OFF, spike_filter=PASS
[HTTP] GET /set?no6=0
[HUB] 200 OK - slot no6=OFF
[WARN] if burner_temp > 80C while away, send alert

• If Connected or connected appears, the Wi-Fi step passed.
• If HTTP 200 or 200 OK appears, the value reached the brain server.
• If the value does not update, check both the slot number in the URL and the sensor wiring.

Build notes

• Test with a short heating period and watch the temperature rise. Decide your own threshold after seeing the normal idle and cooking values.
• Power on the hub brain first so the node can join IoT_Hub_Net.
• Use the same slot number written in the source code.
• Open the serial monitor at 115200 baud and confirm HTTP 200.
• If the value does not appear on the hub, recheck wiring, GPIO number, and Wi-Fi connection.

Uses for Gas-Stove Detection

Reading burner temperature with a K-type thermocouple and MAX6675, then treating above 50°C as 'cooking', turns a plain thermometer into a home-safety tool.

• Left-on-while-away detection: If 'cooking' stays active while the door sensor opens and no presence is detected, the hub sends a 'stove left on, you went out' alert.
• Cooking-time alerts: Log the moment 50°C is crossed; if it persists over 20-30 minutes, push a 'still simmering, please check' reminder to prevent scorching.
• Elderly / single-person safety: If no cooking signal appears all day, notify family as a wellbeing-check trigger.
• Automatic scenarios: If the threshold holds beyond 60 minutes, switch on the kitchen fan via a smart plug or voice-warn through a smart speaker.

Recommended Placement

• Never in the flame: A tip in the flame exceeds 800°C, past the MAX6675 range, and oxidizes the wire fast. Mount it 3-5cm to the side or above the burner, at the trivet (grate) edge so it catches pot radiation and rising hot air.
• Fixing: Clamp it firmly to a trivet leg with a stainless band or ceramic insulating tube so the tip cannot swing into the flame.
• Clearance from combustibles: Keep the lead at least 10cm from the burner and use heat-resistant insulation (fiberglass, PTFE). Place plastic connectors at a cool spot behind the countertop.

Troubleshooting checkpoints

The node code can look short, but real home installation is affected by placement, power, Wi-Fi quality, and sensor noise. Check these points before letting the node become a decision input for the brain server.

Practical Tips and Cautions

• Threshold tuning: A summer kitchen can hit 35°C ambient, risking false positives. If 50°C is too low, raise it to 55-60°C or also watch the rising slope.
• Residual-heat lag: After the flame is off, the trivet and pot stay above threshold for minutes. Declare 'cooking done' only when temperature falls steadily for 5+ minutes.
• Resolution and noise: The MAX6675 has 0.25°C resolution and about a 0.22s SPI update. Smooth jitter with a 3-5 sample moving average and keep signal wires away from appliance power lines.
• Polarity and extension: K-type has (+)chromel/(-)alumel polarity; reversing it reads backwards. Always extend with K-type compensating cable, not plain copper.
• Burn safety: Install and inspect only with the flame off and everything cooled, and never touch the metal tip barehanded.

FAQ

Q. Does it work on induction? Induction heats the pot itself, so you catch the pot's radiant heat but response is slow. Gas-flame detection is far more accurate.

Q. Must the thermocouple touch the pot? No. Air and radiant heat alone suffice for a 50°C decision; direct contact damages the tip and hinders cooking.

Q. Readings look wrong after a power cut. The MAX6675 needs a few seconds for cold-junction settling. Discard the first few samples after restart.