add class diagram

README.md

@@ -1,2 +1,51 @@
 # smart-oil-heating-control-system
 
+## Software
+### Design
+
+```mermaid
+classDiagram
+Inputs <|-- Control
+Outputs <|-- Control
+Inputs <|-- Safety
+Outputs <|-- Safety
+
+Inputs <|-- HTTP_Metrics
+Outputs <|-- HTTP_Metrics
+Control <|-- HTTP_Metrics
+Safety <|-- HTTP_Metrics
+
+    class Inputs{
+        +loop()
+        +getChamberTemperature()
+        +getOutdoorTemperature()
+        +getInletFlowTemperature()
+        +getReturnFlowTemperature()
+    }
+
+    class Outputs{
+        +getCirculationPumpState()
+        +setCirculationPumpState()
+        +getBurnerState()
+        +setBurnerState()
+    }
+
+    class Control{
+        +loop()
+        -timetable
+    }
+
+    class Safety{
+        + loop()
+        + setSafeState()
+        - checkSensorSanity()
+        + getSafetyState()
+    }
+
+    class HTTP_Metrics{
+        - metrics
+        + event_handler()
+        + connect_wifi()
+        + setMetrics()
+    }
+```