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temp_sensor/README.md

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+# Temperature sensor
+
+It uses a [TMP36](https://cloud.hodos.ro/wiki/ha/datasheets/TMP35_36_37.pdf) to read temperature and it is optimised for power consumption.  
+It uses watch dog that wakes every 8s and increments a counter. Once the counter reaches a certain value (e.g. equivalent to 5 mins), it will read and send temperature to the gateway.  
+Every hour the voltage is also read and sent.
+
+According to the calculator here, https://www.geekstips.com/battery-life-calculator-sleep-mode/, a cell coin battery with a capacity of `240mAh` should last for 
+`~ 3 months (108 days)`, given that:
+- Current consumption of device during sleep is `4.5uA`
+- Device wakes up every `5 mins (12 times/hour)`
+- Current consumption of device during wake is `10mA`
+- Duration of wake time is `1000 ms`
+
+![Schematics](docs/temp_sensor_bb.png)