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Fixing Extreme -128dB Wi-Fi Readings On ESPHome ESP32

Alex Johnson
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Fixing Extreme -128dB Wi-Fi Readings On ESPHome ESP32

Hey there, fellow smart home enthusiasts and DIY tinkerers! If you're using an ESPHome ESP32 device, especially one that cycles through deep_sleep to conserve battery, you might have encountered a peculiar and frustrating issue: occasional Wi-Fi signal strength readings of -128dB. This isn't just a bad signal; it's practically a black hole of connectivity! In this article, we're going to dive deep into understanding why your ESP32 might be reporting such an extreme value, why it seems to happen right when your device wakes up, and most importantly, how we can troubleshoot and implement practical solutions to get those Wi-Fi signal readings looking much healthier.

Imagine you have a smart greenhouse monitor, diligently sending sensor data from the far reaches of your garden. It’s powered by an ESP32-S3, happily sleeping for 30 minutes, then waking up for 3 minutes to report vital statistics like battery voltage and, of course, Wi-Fi signal strength. Everything seems fine until one day, you start noticing strange spikes – Wi-Fi signal strength dropping to an almost impossible -128dB, just for a moment, before bouncing back to normal. This isn't just an aesthetic problem; these false readings can skew your monitoring data and trigger unnecessary alerts. Let's unpack this mystery together and make sure your ESPHome devices are reporting the most accurate Wi-Fi connection data possible.

Understanding the Mystery: Why -128dB Wi-Fi Signal?

The -128dB Wi-Fi signal reading is a puzzling phenomenon that many ESPHome users, especially those leveraging the power-saving deep_sleep feature on their ESP32 devices, have encountered. What does -128dBm actually signify? In the world of Wi-Fi, signal strength is measured in dBm (decibels-milliwatts), and values typically range from around -30dBm (excellent) to -90dBm (very poor, barely usable). A reading of -128dBm is extremely low, effectively representing a complete lack of a signal, or a value that the system defaults to when it simply doesn't know what the signal strength is. This isn't a realistic measurement of an actual, physical Wi-Fi signal in most scenarios; rather, it often indicates an internal state within the device's firmware or software logic.

For our greenhouse ESP32-S3, which follows a rigorous deep_sleep cycle, this issue becomes particularly relevant. The device wakes up, quickly attempts to establish a Wi-Fi connection, and then reports its sensor values. The critical insight, as observed in the provided logs, is that these extreme -128dB (or -127dB in the specific log) Wi-Fi signal strength readings appear before the Wi-Fi component is officially marked as Connected. Look closely at the timestamps: the Signal strength: -127 dB reading appears at 17:35:15.613, while the [I][wifi:1079]: Connected status isn't logged until 17:35:17.171. This short window, where the device is initializing but not yet fully connected, seems to be the culprit. It's highly probable that the ESPHome Wi-Fi signal sensor, upon initialization and before a stable Wi-Fi connection is established, reports a default or placeholder value. This value, for whatever reason, is set to an arbitrary extremely low number like -128dBm, representing an 'unknown' or 'not connected' state.

Another layer of complexity stems from how ESPHome handles sensor readings in such intermittent operation modes. When the ESP32 wakes from deep_sleep, it rapidly gathers sensor data. If the Wi-Fi component isn't fully initialized and connected at the precise moment the Wi-Fi signal sensor takes its first reading, that initial, potentially erroneous, value might be buffered by ESPHome. Once the Wi-Fi connection is finally established, and the device has a stable link to Home Assistant, these buffered readings are then sent. This explains why you might see a -128dBm value pop up in your Home Assistant history after the device reports being connected, even though the internal log shows it was measured beforehand. It’s like sending a draft email – you might hit send even if the content isn't fully finalized, and the recipient gets it as is. Understanding this timing is crucial for debugging and implementing effective filters to prevent these misleading Wi-Fi signal strength values from cluttering your data.

Diving Deeper: The ESPHome Deep Sleep Cycle and Wi-Fi Behavior

The core of this issue often lies within the unique operational cycle of devices utilizing ESPHome deep sleep. Our greenhouse ESP32-S3 is a perfect example: it goes into a power-saving deep_sleep state for 30 minutes, wakes up, performs its tasks (reporting sensor values and Wi-Fi connection status), and then returns to sleep. This design is fantastic for battery life, but it introduces specific challenges for Wi-Fi connectivity and firmware updates. Each wake-up cycle requires the ESP32 to re-initialize its Wi-Fi component, scan for networks, authenticate, and establish a connection. This process, while usually fast, isn't instantaneous. During this critical Wi-Fi connection establishment phase, the Wi-Fi signal sensor might be polled, leading to those pre-connection default values.

When attempting to troubleshoot such intermittent issues, especially with a device that has a small awake window, even applying firmware updates can become a hurdle. Imagine trying to update a system that's only awake for a mere three minutes! The original attempts to update the firmware might not have fully succeeded due to this tight window, leaving the device running an older version or a partially updated one, which could explain the persistence of the issue despite update attempts. The effort to move the ESP32 to a workbench for direct monitoring of TX/RX GPIO pins and trying to trim down the YAML configuration were excellent diagnostic steps, aiming to isolate variables. These attempts highlight the dedication required to debug devices in remote or power-constrained environments.

Interestingly, a glimmer of hope appeared after a more thorough firmware update on December 7th. After cleaning build files, recompiling the full greenhouse.yaml using ESPHome 2025.11.4, and uploading it to the ESP32, the extreme -128dB Wi-Fi signal strength values vanished for six days. This suggested that one of the ESPHome 2025.11.x updates might have quietly fixed the underlying bug, or perhaps the clean recompile process itself resolved a subtle configuration issue. However, the problem resurfaced, indicating that the fix was either incomplete, temporary, or contingent on specific environmental factors. This recurrence underscores that the issue might be deeply rooted in the timing of sensor reporting relative to Wi-Fi connection establishment, rather than a simple firmware bug that was patched. It reinforces the theory that the early sensor readings are being buffered and sent once the Wi-Fi connection is fully functional, meaning the device is connected, but it's sending an old, incorrect value from its pre-connection state. This detailed history of troubleshooting provides valuable clues for formulating a robust solution that goes beyond simple firmware updates and focuses on intelligent data handling within ESPHome's configuration.

Analyzing the Logs: Pinpointing the Pre-Connection Reading

Careful analysis of the ESPHome logs is incredibly insightful when trying to understand these anomalous Wi-Fi signal strength readings. The provided USB log snippet offers a clear picture of what's happening internally during the ESP32's wake-up sequence. Let's break down the critical moments. At 2025-12-14 17:35:14.813, the log states [W][component:307]: wifi set Warning flag: associating to network, indicating that the Wi-Fi component is starting its connection process. Fast forward to 17:35:15.613, and we see Signal strength: -127 dB ××××. Notice how this occurs before any explicit message confirming a Wi-Fi connection has been established. At this point, the ESP32 is still actively trying to associate with the network, and its internal Wi-Fi module might be reporting a default or pre-connection status that translates to an extremely low dBm value.

The crucial turning point comes at 17:35:17.171, where the log proudly announces [I][wifi:1079]: Connected. This is the moment your ESP32 successfully establishes its Wi-Fi connection to the router. Immediately after, at 17:35:17.193, the Signal strength is reported again, this time with a healthy -50 dB ▂▄▆█. This sequence of events strongly supports the hypothesis: the -127 dBm reading is a momentary artifact from the Wi-Fi module's initialization phase, occurring before a stable Wi-Fi connection is made. The problem isn't that your Wi-Fi is actually that bad; it's that the sensor is reporting too early.

These early sensor readings, even if erroneous, are then likely buffered by ESPHome. Because the device is designed to be awake for only three minutes and needs to send its data efficiently, ESPHome collects these values. Once the Wi-Fi connection is solid and the API connection to Home Assistant is established (seen at 17:35:18.191 and 17:35:18.208), all the buffered sensor states are pushed through. This explains why Home Assistant's history shows the -127dBm reading at 5:35:18 PM – it's the timestamp when Home Assistant received the buffered data, not necessarily when the measurement was truly taken. This delay in reporting, combined with the pre-connection default, creates the misleading data point. To combat this, we need to consider ways to either delay sensor reporting or implement robust filtering within our ESPHome YAML configuration to specifically ignore these known problematic values. Understanding the precise timing in the logs is the key to crafting a targeted and effective solution that ensures only meaningful Wi-Fi signal data is recorded and sent to your Home Assistant setup.

Practical Solutions and Next Steps for Your Greenhouse Monitor

To combat these misleading -128dB Wi-Fi signal readings, we need to implement smart strategies within your ESPHome YAML configuration. Since the logs clearly show the erroneous reading occurs before a stable Wi-Fi connection, our focus should be on either delaying the reporting of the Wi-Fi signal sensor or filtering out values that are definitively indicative of a pre-connection state. Here are some practical solutions and next steps you can take to refine your greenhouse monitor's data integrity:

  1. Implement a Delay or On_Connect Trigger for Sensor Reporting: The most direct approach is to ensure the Wi-Fi signal sensor only reports its state once a stable Wi-Fi connection has been confirmed. You can achieve this using an on_connect trigger in your ESPHome YAML. Instead of simply update_interval, you could use a lambda or automation that publishes the Wi-Fi signal sensor state only after the wifi.connected event is triggered. This would look something like:

    wifi:
  # ... your existing Wi-Fi configuration ...
  on_connect:
    then:
      - sensor.update: wifi_signal_db # Trigger an update for your Wi-Fi signal sensor

sensor:
  - platform: wifi_signal
    name: "WiFi Signal dB"
    id: wifi_signal_db
    update_interval: never # Prevent automatic updates
    # ... other configurations ...

    This ensures that the sensor is explicitly updated only when Wi-Fi is truly connected, avoiding any pre-connection defaults.

  2. Filter Out Extreme Values with Lambda or Filter: An alternative or complementary approach is to use filters directly on the Wi-Fi signal sensor. ESPHome provides powerful filtering capabilities. You can add a lambda filter that simply discards any value equal to -128.0 (or -127.0, based on your logs) before it's ever published. This acts as a safeguard against any initial, erroneous readings slipping through. A filter block would look like this:

    sensor:
  - platform: wifi_signal
    name: "WiFi Signal dB"
    filters:
      - lambda: if (x == -128.0 || x == -127.0) { return {}; } return x;
    # ... other configurations ...

    This snippet checks if the incoming value x is either -128.0 or -127.0 and, if so, returns an empty result, effectively discarding the measurement. Otherwise, it returns the actual value x.

  3. Review Wi-Fi Component Configuration: While unlikely to be the primary cause of this specific -128dBm issue, it's always good practice to review your wifi component settings. Parameters like reboot_timeout or power_save_mode can influence how quickly and reliably your ESP32 reconnects. Ensuring power_save_mode is set appropriately for your device (e.g., LIGHT or NONE if you prioritize quick reconnection over ultimate power savings during the active phase) might marginally improve Wi-Fi connection speed.

  4. Hardware Check for Stability: Even though the issue seems software-related, it's wise to ensure your hardware setup is robust. Since your ESP32-S3 is in a greenhouse, environmental factors are at play. Double-check your Wi-Fi antenna connection – a loose antenna can cause intermittent poor signals. Also, monitor your LiPo battery voltage not just generally, but specifically for any significant dips during the wake-up and Wi-Fi connection phase. A sudden voltage drop could theoretically affect the Wi-Fi module's performance, although less likely to cause a consistent -128dBm default.

  5. Engage with the ESPHome Community: Don't hesitate to share your detailed findings, especially the log analysis, on the official ESPHome forums or their GitHub issue tracker. The developers and community members often provide valuable insights and might even implement internal fixes for such edge cases. You've already done excellent detective work, and that information can be crucial for the broader ESPHome ecosystem.

By implementing a combination of these strategies, particularly the on_connect trigger or intelligent filters, you can significantly improve the accuracy and reliability of your Wi-Fi signal strength readings. This ensures that your Home Assistant setup receives only valid data, making your greenhouse monitoring system even more robust and trustworthy.

Conclusion

We've taken a deep dive into the perplexing world of -128dB Wi-Fi signal readings on ESPHome ESP32 devices, particularly those operating with deep_sleep. We discovered that these extreme values are likely an artifact of the Wi-Fi component initializing before a stable Wi-Fi connection is established, with these pre-connection readings often being buffered and sent later. This intricate dance between deep_sleep, Wi-Fi connection timing, and sensor reporting can lead to skewed data in your Home Assistant history.

Fortunately, with the powerful customization options in ESPHome YAML, we have several tools at our disposal. By carefully configuring on_connect triggers, implementing robust filters to discard erroneous values, and ensuring your firmware updates are applied correctly, you can dramatically improve the accuracy of your Wi-Fi signal strength monitoring. Your greenhouse monitor deserves to send reliable data, and by understanding these nuances, you're well on your way to a more stable and smarter setup. Keep experimenting, keep monitoring, and keep learning!

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