56 lines
No EOL
3.7 KiB
Markdown
56 lines
No EOL
3.7 KiB
Markdown
# Bluetooth Low Energy (BLE)
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In this saple, b-parasite sensors are periodically read and broadcast using Bluetooth Low Energy (BLE) dvertising packets.
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## Configuration
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Available configurations and their default values are in [`Kconfig`](./Kconfig). They are set in [`prj.conf`](./prj.conf). Here are some notable examples.
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### Sleep Interval
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To save energy, the board spends most of the time in a "deep sleep" state, in which most peripherals and radio are completely turned off. The period of sleep is controlled by the `PRST_SLEEP_DURATION_SEC` config.
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### Advertising Duration
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When it wakes up, the sample reads all sensors and keep broadcasting advertising packets for `PRST_BLE_ADV_DURATION_SEC` before going back to sleep.
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### Advertising Packet Encoding
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There are different ways to encode the sensor data in a BLE advertising packet.
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#### BTHome Encoding
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[BTHome](https://bthome.io) is a new (as of Dec/2022) open standard for encoding sensor data in BLE applications. [Home Assistant](https://www.home-assistant.io/integrations/bthome/) supports it out of the box. This makes the deployment extra convenient, since no additional configuration is needed - Home Assistant will automatically detect b-parasites in range.
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What's even more interesting is that by employing [ESPHome](https://esphome.io/) bridges with the [`bluetooth_proxy`](https://esphome.io/components/bluetooth_proxy.html) component, the range of BLE coverage can be transparently increased. Multiple ESPHome bridges will forward received BLE broadcasts to Home Assistant.
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This is what a typical deployment with BTHome looks like:
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There are two versions of BTHome encodings supported by this sample:
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* `PRST_BLE_ENCODING_BTHOME_V1=y` uses the [legacy BTHome V1](https://bthome.io/v1/), which was briefly in use
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* `PRST_BLE_ENCODING_BTHOME_V2=y` uses the [BTHome V2](https://bthome.io/format/), which is not yet (as of early Dec/2022) in the stable Home Assistant release. This will soon become the default.
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#### b-parasite Encoding
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`PRST_BLE_ENCODING_BPARASITE_V2=y` selects the "legacy" encoding, used historically inn this project. This is the encoding that the [`b_parasite`](https://esphome.io/components/sensor/b_parasite.html) ESPHome component understands.
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With this encoding and a ESPHome + `b_parasite` component, this is an usual deployment topology:
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The disadvantages of this encoding are:
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- Each b-parasite has to be configured in the ESPHome component
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- Range is limited, unless multiple ESPHome bridges are deployed with the same static configuration
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## Battery Life
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**tl;dr**: Theoretically well over two years with default settings.
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While in deep sleep, the board consumes around `3.0 uA`:
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In the active broadcasting state, the average power consumption is highly dependant on the advertising interval.
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With the default settings (in the `[30, 40] ms` range), we see an average of around `810 uA`:
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If for example we lower the connection interval to the SDK defaults (`[100, 150] ms`, roughly trading off range for power), the average current consumption is around `345 uA`:
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With a `200 mAh` CR2032 battery, we can use [this spreadsheet](https://docs.google.com/spreadsheets/d/157JQiX20bGkTrlbvWbWRrs_WViL3MgVZffSCWRR7uAI/edit#gid=0) to estimate the battery life to over two years. Note that this is a simplified model and results in practice may vary. |