Add docs

README.md

@@ -21,6 +21,7 @@ This repository also hosts a few different firmware samples for b-parasite.
 |Sample|Description|Extra Documentation|
 |---|---|---|
 |[samples/ble](./code/nrf-connect/samples/ble)|This is the most battle-tested and useful firmware. It periodically reads all sensors and broadcast them via Bluetooth Low Energy (BLE). It works with [Home Assistant](https://www.home-assistant.io/) out of the box. |[Docs](./code/nrf-connect/samples/ble/README.md)|
+|[samples/zigbee](./code/nrf-connect/samples/zigbee)| A new, experimental Zigbee sample. It integrates with [Home Assistant](https://www.home-assistant.io/) via [Zigbee2MQTT](https://www.zigbee2mqtt.io/). |[Docs](./code/nrf-connect/samples/zigbee/README.md)|
 |[samples/blinky](./code/nrf-connect/samples/blinky)| The classic "Hello, world" |-|
 |[samples/soil_read_loop](./code/nrf-connect/samples/soil_read_loop)| Read the soil moisture sensor on a loop. Useful for experimenting and calibrating the sensor. |-|
 

code/nrf-connect/samples/zigbee/README.md

@@ -0,0 +1,42 @@
+# Zigbee firmware sample
+This sample is adapted from the [zigbee_template](https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrf/samples/zigbee/template/README.html) from the nRF Connect SDK.
+
+## Clusters
+These [clusters](https://en.wikipedia.org/wiki/Zigbee#Cluster_library) are defined in the sample:
+
+|Cluster ID|Name|
+|--------|---|
+|0x0001|Power Configuration|
+|0x0400|Illuminance Measurement|
+|0x0402|Temperature Measurement|
+|0x0405|Relative Humidity Measurement|
+|0x0408|Soil Moisture Measurement|
+
+## Pairing Mode
+The sample will first boot and start looking for a Zigbee coordinator - in pairing mode. The onboard LED will be flashing once a second while in this mode. Once a suitable network is found, the LED will briefly flash 3 times and remain off.
+
+### Factory Reset
+Most Zigbee devices provide a physical button to "factory reset" it - causing it to forget its joined network and look for a new one.
+
+b-parasite has no physical buttons, and the implemented work around is to distinguish between two *reset modes*:
+#### Power up mode
+The device enters this mode when it is powered. For example, swapping an old battery or connecting to eternal power. This is the "usual" reset mode, and joined networks will be remembered.
+
+#### Reset pin mode
+If the device's RESET pin is briefly grounded, the device will effectively be **factory reset**. The device will leave its previous network and start looking for a new one.
+
+## Configs
+Available options in `Kconfig`. Notable options:
+* `CONFIG_PRST_ZB_SLEEP_DURATION_SEC`: amount of time (in seconds) the device sleeps between reading all sensors and updating its clusters
+* `CONFIG_PRST_ZB_PARENT_POLL_INTERVAL_SEC`: amount of time (in seconds) the device waits between polling its parent for data
+
+## Zigbee2MQTT & Home Assistant
+This firmware sample has only been tested with [Zigbee2MQTT](https://zigbee2mqtt.io/), an open source Zigbee bridge that [connects seamlessly with Home Assistant](https://github.com/zigbee2mqtt/hassio-zigbee2mqtt).
+
+The [b-parasite.js](b-parasite.js) file contains a converter that can be installed to Zigbee2MQTT to suppoort this sample. See [Support new devices](https://www.zigbee2mqtt.io/advanced/support-new-devices/01_support_new_devices.html) for instructions.
+
+## Battery Life
+While sleeping, the device consumes around 2 uA:
+![sleeping current](./media/power-profile/sleeping.png)
+In the active cycle, it averages around 370 uA for 2.6 seconds:
+![active current](media/power-profile/active.png)