fix(sim): correct NTC temperature sensor divider + reset to default on restart

The NTC breakout's SPICE topology was inverted relative to the example
sketch's decode formula (rNtc = R_PULL * v / (5 - v)), which assumes a 10k
pull-up from VCC to OUT and the NTC from OUT to GND. The mapper had the NTC
on top (VCC->OUT) and the pull-down on the bottom, so the recovered
temperature ran backwards: dragging the slider to 100C made the sketch
print -25C. Swap the two resistors so V_OUT = 5 * Rntc / (Rntc + Rpull),
matching the sketch and the hand-built reference netlist in
spice-avr-mixed.test.ts (T=0 -> ADC 789, T=25 -> 511, T=50 -> 270).

Also replace the SensorParts linear approximation (2.5 - (t-25)*0.02) with
the same beta-model divider so the non-SPICE ADC injection decodes back to
the slider value, and drop the dead onInput path that treated the element's
value as a raw ADC count.

Reset now restores interactive sensors (temperature/lux/gas sliders) to
their configured defaults: resetBoard re-dispatches each sensor's default
into the running sim and bumps sensorResetNonce so the open
SensorControlPanel remounts and the slider snaps back. Previously a restart
left the NTC frozen at the last dragged temperature.

Updated the examples netlist snapshot for the swapped NTC cards.

frontend/src/__tests__/__snapshots__/examples-netlist-snapshot.test.ts.snap

@@ -1416,8 +1416,8 @@ R_autopull_n6 n6 0 100Meg
 exports[`netlist snapshot — circuits (41 examples) > nano-sensor-station 1`] = `
 "* Velxio circuit
 V_VCC_RAIL vcc_rail 0 DC 5
-R_ntc_ntc vcc_rail n1 11441.484668193882
+R_ntc_pull vcc_rail n1 10000
-R_ntc_pull n1 0 10000
+R_ntc_ntc n1 0 11441.484668193882
 R_ldr_ldr vcc_rail n0 400000
 R_ldr_pull n0 0 10000
 .op
@@ -1446,8 +1446,8 @@ R_autopull_n5 n5 0 100Meg
 exports[`netlist snapshot — circuits (41 examples) > ntc-temperature 1`] = `
 "* Velxio circuit
 V_VCC_RAIL vcc_rail 0 DC 5
-R_ntc_ntc vcc_rail n0 10000
+R_ntc_pull vcc_rail n0 10000
-R_ntc_pull n0 0 10000
+R_ntc_ntc n0 0 10000
 .op
 .end"
 `;

frontend/src/components/simulator/SimulatorCanvas.tsx

@@ -118,6 +118,7 @@ export const SimulatorCanvas = ({ headerSlot }: SimulatorCanvasProps = {}) => {
     addBoard,
     components,
     running,
+    sensorResetNonce,
     pinManager,
     initSimulator,
     updateComponentState,
@@ -2490,14 +2491,15 @@ export const SimulatorCanvas = ({ headerSlot }: SimulatorCanvasProps = {}) => {
               key={sensorControlComponentId} forces a fresh mount when the user clicks a
               different instance of the same sensor type (e.g. a second photoresistor); the
               slider state is local and would otherwise show the previously-clicked sensor's
-              value until the user manually moved it. */}
+              value until the user manually moved it. The sensorResetNonce suffix also remounts
+              it on Reset, so the slider snaps back to the sensor's default value. */}
           {sensorControlComponentId &&
             sensorControlMetadataId &&
             (() => {
               const meta = registry.getById(sensorControlMetadataId);
               return (
                 <SensorControlPanel
-                  key={sensorControlComponentId}
+                  key={`${sensorControlComponentId}:${sensorResetNonce}`}
                   componentId={sensorControlComponentId}
                   metadataId={sensorControlMetadataId}
                   sensorName={meta?.name ?? sensorControlMetadataId}

frontend/src/simulation/parts/SensorParts.ts

@@ -62,26 +62,29 @@ PartSimulationRegistry.register('tilt-switch', {
  * NTC thermistor sensor — injects analog voltage representing temperature.
  * Default 25°C → 2.5V. SensorControlPanel slider adjusts temperature.
  *
- * Linear approximation: volts = clamp(2.5 - (temp - 25) * 0.02, 0, 5)
+ * The injected OUT voltage uses the SAME β-model voltage divider the circuit
- * (25°C = 2.5V; lower temp = higher voltage, higher temp = lower voltage)
+ * (and the example sketch) assume: a 10k pull-up from VCC to OUT and the NTC
+ * from OUT to GND, so V_OUT = 5 · R_ntc / (R_ntc + R_pull) with
+ * R_ntc(T) = R0 · exp(β · (1/T − 1/T0)).  This makes the injected ADC voltage
+ * decode straight back to the slider value (set 50°C → read 50°C).  When the
+ * electrical (SPICE) engine is active it drives A0 from the ngspice solve
+ * instead, using the matching topology in componentToSpice.ts — both agree.
  */
 PartSimulationRegistry.register('ntc-temperature-sensor', {
-  attachEvents: (element, simulator, getArduinoPinHelper, componentId) => {
+  attachEvents: (_element, simulator, getArduinoPinHelper, componentId) => {
     const pin = getArduinoPinHelper('OUT');
 
-    const tempToVolts = (temp: number) => Math.max(0, Math.min(5, 2.5 - (temp - 25) * 0.02));
+    const NTC_R0 = 10_000;
+    const NTC_BETA = 3950;
+    const R_PULL = 10_000;
+    const tempToVolts = (temp: number) => {
+      const rNtc = NTC_R0 * Math.exp(NTC_BETA * (1 / (temp + 273.15) - 1 / 298.15));
+      return Math.max(0, Math.min(5, 5 * (rNtc / (rNtc + R_PULL))));
+    };
 
     // Room temperature default
     if (pin !== null) setAdcVoltage(simulator, pin, tempToVolts(25));
 
-    const onInput = () => {
-      const val = (element as any).value;
-      if (val !== undefined && pin !== null) {
-        setAdcVoltage(simulator, pin, (val / 1023.0) * 5.0);
-      }
-    };
-    element.addEventListener('input', onInput);
-
     registerSensorUpdate(componentId, (values) => {
       if ('temperature' in values) {
         if (pin !== null) {
@@ -94,7 +97,6 @@ PartSimulationRegistry.register('ntc-temperature-sensor', {
     });
 
     return () => {
-      element.removeEventListener('input', onInput);
       unregisterSensorUpdate(componentId);
     };
   },

frontend/src/simulation/spice/componentToSpice.ts

@@ -700,9 +700,11 @@ const MAPPERS: Record<string, Mapper> = {
   },
 
   // NTC temperature sensor — 3-pin breakout module (VCC, GND, OUT).
-  // Internal topology: NTC thermistor between VCC and OUT, plus an internal
+  // Internal topology: a 10k pull-up from VCC to OUT, with the NTC thermistor
-  // 10k pull-down from OUT to GND. Temperature up → R_ntc down → V_OUT up.
+  // from OUT to GND, so V_OUT = Vcc · R_ntc / (R_ntc + R_pull). Temperature up
-  // Matches the β-model math used in the ntc-temperature example.
+  // → R_ntc down → V_OUT down. This is the exact divider the ntc-temperature
+  // example sketch inverts to recover R_ntc (rNtc = R_PULL · v / (5 − v)); with
+  // VCC and GND swapped (NTC on top) the decoded temperature ran backwards.
   'ntc-temperature-sensor': (comp, netLookup) => {
     const vcc = netLookup('VCC');
     const gnd = netLookup('GND');
@@ -719,7 +721,7 @@ const MAPPERS: Record<string, Mapper> = {
     }
     const Rpull = parseValueWithUnits(comp.properties.pullup, 10_000);
     return {
-      cards: [`R_${comp.id}_ntc ${vcc} ${out} ${Rntc}`, `R_${comp.id}_pull ${out} ${gnd} ${Rpull}`],
+      cards: [`R_${comp.id}_pull ${vcc} ${out} ${Rpull}`, `R_${comp.id}_ntc ${out} ${gnd} ${Rntc}`],
       modelsUsed: new Set(),
     };
   },

frontend/src/store/useSimulatorStore.ts

@@ -37,6 +37,8 @@ import {
   updateWires as icUpdateWires,
   setInterconnectRuntime,
 } from '../simulation/Interconnect';
+import { SENSOR_CONTROLS } from '../simulation/sensorControlConfig';
+import { dispatchSensorUpdate } from '../simulation/SensorUpdateRegistry';
 
 // ── Sensor pre-registration ──────────────────────────────────────────────────
 // Maps component metadataId → { sensorType, dataPinName, propertyKeys }
@@ -817,6 +819,9 @@ interface SimulatorState {
   running: boolean;
   compiledHex: string | null;
   hexEpoch: number;
+  /** Bumped on every Reset so the open SensorControlPanel remounts and
+   *  re-reads each interactive sensor's freshly-defaulted value. */
+  sensorResetNonce: number;
   serialOutput: string;
   serialBaudRate: number;
   serialMonitorOpen: boolean;
@@ -1914,6 +1919,29 @@ export const useSimulatorStore = create<SimulatorState>((set, get) => {
           ...(isActive ? { running: false, serialOutput: '', serialBaudRate: 0 } : {}),
         };
       });
+
+      // Reset interactive sensors (temperature / lux / gas sliders, etc.) back
+      // to their configured defaults so a restart starts from a clean state
+      // instead of freezing on the last slider position the user dragged to.
+      // dispatchSensorUpdate re-injects the default into the running sim (so the
+      // NTC's injected ADC voltage and the SPICE solve both return to 25°C /
+      // 2.5V) and refreshes the panel's cached value; bumping sensorResetNonce
+      // remounts the open SensorControlPanel so its slider snaps back too.
+      const sensorComps = get().components.filter(
+        (c) => c.metadataId && SENSOR_CONTROLS[c.metadataId],
+      );
+      if (sensorComps.length > 0) {
+        set((s) => ({
+          components: s.components.map((c) => {
+            const def = c.metadataId ? SENSOR_CONTROLS[c.metadataId] : undefined;
+            return def ? { ...c, properties: { ...c.properties, ...def.defaultValues } } : c;
+          }),
+          sensorResetNonce: s.sensorResetNonce + 1,
+        }));
+        for (const c of sensorComps) {
+          dispatchSensorUpdate(c.id, SENSOR_CONTROLS[c.metadataId].defaultValues);
+        }
+      }
     },
 
     // ── Legacy single-board API ───────────────────────────────────────────
@@ -1924,6 +1952,7 @@ export const useSimulatorStore = create<SimulatorState>((set, get) => {
     running: false,
     compiledHex: null,
     hexEpoch: 0,
+    sensorResetNonce: 0,
     serialOutput: '',
     serialBaudRate: 0,
     serialMonitorOpen: false,