update README

README.md

@@ -9,6 +9,35 @@ ESP32-based control system for oil-fired central heating with schedule-based tem
 - **Safety Monitoring**: Sensor sanity checks with automatic safe-state fallback
 - **Prometheus Metrics**: HTTP endpoint at port 9100
 
+## System Overview
+```mermaid
+flowchart TB
+    subgraph OUTSIDE[" "]
+        OT[/"🌡️ Outdoor Temp<br/>DS18B20"/]
+    end
+
+    subgraph BURNER["OIL BURNER"]
+        CT[/"🌡️ Chamber Temp<br/>DS18B20"/]
+        BF[["⚠️ Burner Fault<br/>GPIO19 INPUT"]]
+        BR(["🔥 Burner Relay<br/>GPIO14"])
+        SC(["🔌 Safety Contact<br/>GPIO12"])
+    end
+
+    subgraph CIRCUIT["HEATING CIRCUIT"]
+        IT[/"🌡️ Inlet Temp<br/>DS18B20"/]
+        CP(["💧 Circulation Pump<br/>GPIO27"])
+        RT[/"🌡️ Return Temp<br/>DS18B20"/]
+    end
+
+    RAD["🏠 Radiators"]
+
+    BURNER -->|"hot water"| IT
+    IT --> CP
+    CP --> RAD
+    RAD --> RT
+    RT -->|"cold water"| BURNER
+```
+
 ### Prometheus Metrics
 `curl http://X.X.X.X:9100/metrics`
 #### Example
@@ -17,26 +46,26 @@ burner_fault_pending 1
 circulation_pump_enabled 1
 burner_enabled 0
 safety_contact_enabled 1
-chamber_temperature 37.250000
-chamber_temperature_avg10 37.237499
-chamber_temperature_avg60 37.438541
-chamber_temperature_damped 42.185040
-chamber_temperature_pred60 36.638443
-inlet_flow_temperature 35.625000
-inlet_flow_temperature_avg10 35.618752
-inlet_flow_temperature_avg60 35.415627
-inlet_flow_temperature_damped 39.431259
-inlet_flow_temperature_pred60 36.078678
-outdoor_temperature 14.687500
-outdoor_temperature_avg10 14.662500
-outdoor_temperature_avg60 14.646875
-outdoor_temperature_damped 9.169084
-outdoor_temperature_pred60 14.660233
-return_flow_temperature 39.937500
-return_flow_temperature_avg10 40.087502
-return_flow_temperature_avg60 41.146873
-return_flow_temperature_damped 32.385151
-return_flow_temperature_pred60 37.311958
+chamber_temperature 37.312500
+chamber_temperature_avg10 37.393749
+chamber_temperature_avg60 37.689583
+chamber_temperature_damped 38.058098
+chamber_temperature_pred60 36.697266
+inlet_flow_temperature 34.562500
+inlet_flow_temperature_avg10 34.587502
+inlet_flow_temperature_avg60 34.880207
+inlet_flow_temperature_damped 35.255993
+inlet_flow_temperature_pred60 33.910374
+outdoor_temperature 1.812500
+outdoor_temperature_avg10 1.825000
+outdoor_temperature_avg60 1.821875
+outdoor_temperature_damped 2.390663
+outdoor_temperature_pred60 1.840263
+return_flow_temperature 34.125000
+return_flow_temperature_avg10 34.162498
+return_flow_temperature_avg60 34.304165
+return_flow_temperature_damped 31.430506
+return_flow_temperature_pred60 33.858772
 chamber_temperature_state 0
 outdoor_temperature_state 0
 inlet_flow_temperature_state 0
@@ -44,13 +73,13 @@ return_flow_temperature_state 0
 safety_state 0
 control_state 3
 control_current_weekday 5
-control_current_entry_time 17100
+control_current_entry_time 24300
 control_current_entry_chamber_temperature 80.000000
 control_current_entry_return_flow_temperature 30.000000
 sntp_state 0
-system_unixtime 1762012743
-uptime_seconds 465229
-wifi_rssi -72
+system_unixtime 1768067412
+uptime_seconds 344878
+wifi_rssi -59
 ```
 
 #### Status Encoding