IoT LPG Cylinder Level Monitor with Refill Booking Alerts

Most households discover the cylinder is empty the moment the burner dies mid-cooking. Lifting the cylinder to guess the gas left is the common workaround, and it is unreliable — a 14.2 kg domestic cylinder's steel body weighs roughly 15 kg on its own, so "feels half" is mostly imagination. This project solves the problem the engineering way: it weighs the cylinder. A 50 kg single-point load cell sits under a steel weighing platform; an HX711 24-bit ADC digitises the tiny strain-gauge signal; an ESP32 turns raw weight into gas remaining by subtracting the stored tare, and estimates days remaining from the household's rolling average consumption. When the level crosses the alert threshold (20% default, configurable to 10%), the dashboard fires a low-level alert and a one-tap button sets a refill-booking reminder. A local 16x2 LCD shows live weight and status on the rig itself, so the sensing chain is demonstrable without a phone or browser.

1. The LPG cylinder stands on a steel platform supported by a 50 kg single-point load cell; the load cell's four wires feed the HX711 amplifier module.
2. The ESP32 reads the HX711 at gain 128 (channel A), applies moving-average filtering, and converts counts to kilograms using the two-point calibration factor from the buyer's calibration run.
3. On first use the buyer stores the tare (empty cylinder weight, typically ~15 kg for a 14.2 kg domestic cylinder) in flash; gas remaining = total weight − tare.
4. Gas percentage = gas remaining ÷ refill size; the firmware tracks the daily weight drop as a rolling average and computes days remaining = gas remaining ÷ average daily use.
5. The ESP32 wakes from deep sleep every 15 minutes, takes a reading, serves the local dashboard over Wi-Fi, updates the 16x2 LCD, and sleeps again.
6. When the level crosses the alert threshold, the dashboard banner fires and latches the event into the refill-alert log until a refill (weight jump) clears it.
7. The "Book refill" button sets a booking reminder with the distributor details; a weight jump back near full marks the refill as completed in the log.

Tech stack:

• ESP32 (Arduino framework)
• 50 kg single-point load cell · HX711 24-bit ADC module
• Steel weighing platform (fabricated)
• 16x2 LCD (I2C)
• HTML/CSS/JavaScript companion dashboard (single-file)
• Deep-sleep power cycling · moving-average filtering
• Wi-Fi (dashboard + optional MQTT)

• [Weight-based gas level] A 50 kg single-point load cell under a steel platform measures total cylinder weight; firmware subtracts the tare (empty cylinder weight) and divides by the refill size (14.2 / 5 / 19 kg) to report gas percentage.
• [Days-remaining estimate] Daily consumption is learned as a rolling average of the weight drop, and the dashboard converts remaining gas into an estimated days-left figure with a predicted refill date.
• [Low-level alerts] When the level crosses the configured threshold (20% default, 10% option), the dashboard banner turns critical and the event is logged to the refill-alert history until the cylinder is refilled.
• [One-tap refill reminder] A "Book refill" button sets a refill-booking reminder and records it in the alert log, so the workflow from low gas to booked refill is demonstrable in one click.
• [HX711 + ESP32 firmware] 24-bit ADC at gain 128 on channel A, moving-average filtering for stability, deep-sleep wake every 15 minutes, tare stored in flash, two-point calibration through the buyer's own weight procedure.
• [Live web dashboard] Cylinder fill graphic, gas remaining in kg, days-left counter, total/tare weights, 30-day usage chart with alert-threshold line, node status (battery, Wi-Fi RSSI, load-cell state) and configurable alert thresholds.
• [16x2 LCD readout] Live weight and STABLE/ALERT status on the hardware itself, so the prototype is demonstrable standalone.

• Weighing platform prototype (load cell, steel plate, HX711, ESP32, 16x2 LCD, wiring)
• ESP32 firmware source (tare, two-point calibration, filtering, deep-sleep cycle, dashboard server)
• Companion web dashboard (single-file HTML/CSS/JS, the GasWatch demo)
• Load-cell calibration procedure for the buyer
• Project report PDF (background, load-cell/HX711 theory, methodology, circuit diagrams)
• PPT presentation for final review
• Viva Q&A preparation document (strain gauges, HX711, ADC resolution, calibration, deep sleep)

• This is a MONITOR only: it never actuates the cylinder valve and cannot shut off gas — no valve-control hardware or firmware is included.
• It is NOT a gas-leak detector and does not replace one; it measures weight, not gas concentration in air.
• Weight resolution of ~10 g is a design target achieved after filtering and the buyer's own two-point calibration — it is not a measured claim until the calibration run is done on the built unit.
• Accuracy depends on the cylinder standing undisturbed on the platform; moving or leaning the cylinder during a reading skews that sample.
• The days-remaining estimate assumes consumption near the recent average; a sudden change (festival cooking, guests) makes the estimate drift until the average relearns.
• Wi-Fi range limits where the dashboard is reachable; there is no GSM/SMS fallback in the standard build.
• Deep-sleep cycle means readings are 15 minutes apart by design — this is not a real-time safety system.