From my ESP32.com post today:
Project: Heating System Monitor IV with ~50 µA average current; Outside BME280 Node!
Why use Heating System Monitor IV?
Answer questions your thermostat can't. A thermostat knows the setpoint. HSM IV knows what the system actually did: how many minutes the blower ran today, how long each cycle lasted, how long the house held temperature between cycles, and what the indoor and outdoor conditions were at the time. Over days and weeks, that data answers real questions:
• Is my system short-cycling?
• Which thermostat setpoint gives long, efficient cycles instead of frequent short ones?
• How does runtime track outdoor temperature? (Runtime per degree-day is your building's thermal signature — a sudden change flags a filter, refrigerant, or duct problem before the utility bill does.)
• Is the system degrading over time?
No electrical connection to your HVAC system. Blower detection is purely mechanical — an MPU-6050 IMU sensing vibration from outside the blower enclosure. Nothing is wired into the furnace or air handler. Nothing voids a warranty, nothing touches line voltage, and the whole monitor installs and removes without a trace — ideal for renters and apartments.
Owns its data. Every event is logged twice: locally to the ESP32's flash (LittleFS, retrievable over FTP) and to a perpetual Google Sheet that rolls month-to-month and year-to-year automatically. No cloud subscription, no vendor account, no app.
Survives real-world conditions. Runtime totals persist through power failures via NVS flash storage. A reset-reason log distinguishes normal power cycles from brownouts and watchdog resets. If the outdoor sensor node goes silent, its columns log "Offline" instead of silently repeating stale data. The outside node itself runs for years on battery power alone.
README.md includes Nordic Power Profiler Kit 2 Observations of the Outside ~50 µA average current BME280 Node.
73's (Best Regards)
William, AB9NQ
