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 # Oil sensor
 
+Using an ultra sonic sensor, it detects the amount of oil used for heating.
+
+For optimization purposes, it uses 2 microcontrollers:
+#### **Arduino Pro Mini**
+It offers a precise quartz clock, required by the ultra sonic sensor to accurately determine the level of oil in the tank. But because it has a high consumption, it is not suited for battery powered devices.
+#### **ATTiny85**
+It has an inaccurate quartz clock that cannot be used for the sonar sensor, but it is more than enough to be used as a wake-up device for Arduino Pro Mini. Due to the very low power consumption, it is ideal for battery powered devices.
+
+## Mode of operation
+ATTiny85 is connected directly to the battery and acts as a power switch:
+1. on regular intervals, ~6 hours, it powers on the Arduino Pro Mini
+1. Arduino Pro Mini will:
+    - read the oil tank level
+    - send the information to the RC Gateway
+    - signal the ATTiny85 that it has finished
+1. turns off the Arduino Pro Mini
+
 ![Schematics](docs/oil_sensor_bb.png)