FAQ
TL;DR: A 160 µA-idle ESP8266 sensor counts meter-LED flashes; “Scanning the channels takes approximately 300 ms” [Elektroda, efi222, post #21166581] It delivers near-real-time kW data via ESP-NOW and a Wi-Fi receiver webpage.
Why it matters: You see household load changes seconds after they occur—without opening the sealed meter box.
Quick Facts
• Deep-sleep current: 160 µA; wake-to-sleep cycle ≈ 180 ms [Elektroda, efi222, post #21166581]
• Channel scan: 13 Wi-Fi channels in 300 ms [Elektroda, efi222, post #21166581]
• Battery life: 3 Ah 18650 lasts ~5 months @1-min pulses or 9 months @10 s pulses [Elektroda, ex-or, post #21167195]
• Meter constant: 1000 flashes = 1 kWh on common Apator S34U meters [Elektroda, efi222, post #21167400]
• Typical parts cost: 8–12 € (ESP8266, LMV358, LDR, 18650 holder) [Allegro listings, 2024]
What does the remote LED flash detector actually measure?
It measures the time between successive flashes of the meter’s calibration LED (1000 flashes = 1 kWh) and converts that interval into instantaneous power in kilowatts [Elektroda, efi222, post #21167400]
How does the ESP-NOW auto-scan avoid lost packets when the Wi-Fi channel shifts?
After every wake-up, the transmitter sequentially queries all 13 channels until the receiver MAC answers; the found channel is cached in RTC memory, so future wakes skip the 300 ms scan unless two ACKs are missed [Elektroda, efi222, post #21166581]
What current does the sensor draw in each state?
Deep sleep: 160 µA. Wake + transmit: ~40–60 mA average over 180 ms, with 220 mA peaks for just a few milliseconds [Elektroda, efi222, post #21166581]
How long will a 3 Ah 18650 cell power the unit?
≈ 2 years if the LED triggers hourly, 5 months at 1-minute flashes, and ~9 months with a 10-second flash rate [Elektroda, ex-or, post #21167195]
Which light sensor works best for the meter LED?
A GL5516 LDR proved reliable; low dark resistance lowers quiescent current. Changing LDR type may require adjusting the bridge resistor [Elektroda, efi222, post #21166779]
Is temperature drift of the photoresistor a concern?
Drift exists, but the comparator threshold sits midway between bright and dark levels, leaving enough margin that normal outdoor temperature swings don’t cause false triggers [Elektroda, efi222, post #21169975]
Can I switch to a phototransistor to save current?
Yes; a phototransistor generates larger, faster currents, letting you omit the op-amp and drop quiescent draw by tens of microamps, especially if powered from an ESP GPIO [Elektroda, TvWidget, post #21167871]
How is power displayed to the user?
The receiver ESP hosts a local web page refreshed by Ajax; power (kW) updates each time data arrives and cumulative kWh can be added in code [Elektroda, efi222, post #21167358]
What are the main failure modes to watch for?
- Wi-Fi router channel change → temporary data loss until auto-scan runs.
- LDR misalignment or aging → missed flashes.
- Extreme heat may raise LDR resistance, delaying trigger [Elektroda, khoam, post #21169952]
How do I align the sensor with the meter LED?
- Glue or Velcro the boom so the LDR faces the LED directly.
- Close the meter cover; verify no ambient light reaches the LDR.
- Use serial logs to ensure each flash wakes the ESP.
Can Zigbee or BLE cut power further?
Possibly. An ESP32-C6 in Zigbee mode would let the radio sleep longer, trimming average current below 30 µA according to vendor datasheets [Espressif, 2024], though code complexity rises [Elektroda, speedy9, post #21167352]
Is it more accurate than a clamp-based CT solution?
Energy accuracy matches the utility meter because it reuses its LED pulses, but instantaneous power resolution degrades at low loads (<100 W) where pulses arrive >30 s apart; CT meters sample voltage and current every cycle, giving smoother real-time curves [Elektroda, BBElektrotechnik, post #21169763]
Why not just use the meter’s S0/RS-485 output?
Many suppliers lock or disable those terminals, and adding wires inside a sealed box violates regulations; the optical method is completely non-intrusive [Elektroda, efi222, post #21168643]
How could I extend battery life further?
Replace LMV358 with single-op-amp LMV321, power the comparator from an ESP GPIO, and buffer multiple pulses to send aggregated data every few minutes, which one user estimates would cut consumption by an order of magnitude [Elektroda, khoam, post #21167779]
