Add transistors

Media.JoshHeaps.Net/Services/BreadboardValidator.cs

@@ -70,6 +70,7 @@ public class BreadboardValidator(ILogger<BreadboardValidator> logger)
     private const int ChipColumnSpan = 7;        // 14-pin DIP
     private const int DipSwitchColumnSpan = 8;   // 16-pin DIP
     private const int PushButtonColumnSpan = 3;
+    private const int TransistorColumnSpan = 3;   // TO-92, three legs one column apart
     private const int DipSwitchPositions = 8;
 
     private static readonly Regex UidPattern = new($@"^[A-Za-z0-9_.:-]{{1,{MaxUidLength}}}$", RegexOptions.Compiled | RegexOptions.CultureInvariant);
@@ -110,7 +111,8 @@ public class BreadboardValidator(ILogger<BreadboardValidator> logger)
 
     private static readonly HashSet<string> ComponentTypes = new(StringComparer.Ordinal)
     {
-        "led", "resistor", "pushButton", "dipSwitch8", "powerSupply5V",
+        "led", "resistor", "diode", "npn", "pnp", "nmos", "pmos",
+        "pushButton", "dipSwitch8", "powerSupply5V",
         "74HC00", "74HC02", "74HC04", "74HC08", "74HC32", "74HC86", "74HC30"
     };
 
@@ -289,7 +291,21 @@ public class BreadboardValidator(ILogger<BreadboardValidator> logger)
         switch (type)
         {
             case "led":
-                ValidateLed(component, path, boardUids, errors);
+                ValidateTwoHoleSpan(component, path, boardUids, errors);
+                ValidateLedProps(component, path, errors);
+                break;
+
+            case "diode":
+                ValidateTwoHoleSpan(component, path, boardUids, errors);
+                ValidateEmptyProps(component, path, errors);
+                break;
+
+            case "npn":
+            case "pnp":
+            case "nmos":
+            case "pmos":
+                ValidateInlinePackage(component, path, TransistorColumnSpan, boardUids, errors);
+                ValidateEmptyProps(component, path, errors);
                 break;
 
             case "resistor":
@@ -334,15 +350,15 @@ public class BreadboardValidator(ILogger<BreadboardValidator> logger)
     }
 
     /// <summary>
-    /// An LED spans two holes: the anchor is the anode and the cathode sits one hole away in
+    /// A two-legged part spanning two holes: the anchor is the first terminal (an LED's anode,
-    /// the orient direction. A leg in a power rail is legal — electrically useless if both
+    /// a diode's anode) and the second sits one hole away in the orient direction. A leg in a
-    /// legs share a rail, but a real breadboard allows it — so only the footprint is checked.
+    /// power rail is legal — electrically useless if both legs share a rail, but a real
+    /// breadboard allows it — so only the footprint is checked.
     /// </summary>
-    private static void ValidateLed(JsonElement component, string path, HashSet<string> boardUids, ErrorList errors)
+    private static void ValidateTwoHoleSpan(JsonElement component, string path, HashSet<string> boardUids, ErrorList errors)
     {
         var orient = ReadEnum(component, "orient", path, Orientations, errors, required: true);
         var anchor = ReadAnchor(component, path, boardUids, errors, required: true);
-        ValidateLedProps(component, path, errors);
 
         if (anchor is null || orient is null)
         {
@@ -352,7 +368,7 @@ public class BreadboardValidator(ILogger<BreadboardValidator> logger)
         if (orient is "up" or "down")
         {
             // Vertical travel moves one row and may legitimately cross the centre channel. A
-            // rail has no rows, so the cathode of an up/down LED anchored there has nowhere to go.
+            // rail has no rows, so the far leg of an up/down part anchored there has nowhere to go.
             if (anchor.Kind != "main")
             {
                 errors.Add($"{path}.orient", "not_valid_on_rail");
@@ -362,8 +378,8 @@ public class BreadboardValidator(ILogger<BreadboardValidator> logger)
             // Rows a..j read top to bottom, so "up" decreases the row index — the same sign
             // convention that maps "left"/"right" to -1/+1 on the column axis. Mirrors
             // shared/board-geometry.js (team amendment A12 pins it as contract).
-            var cathodeRow = (anchor.Row[0] - 'a') + (orient == "up" ? -1 : 1);
+            var farRow = (anchor.Row[0] - 'a') + (orient == "up" ? -1 : 1);
-            if (cathodeRow < 0 || cathodeRow >= MainRows.Count)
+            if (farRow < 0 || farRow >= MainRows.Count)
             {
                 errors.Add($"{path}.anchor", "footprint_off_board");
             }
@@ -371,16 +387,50 @@ public class BreadboardValidator(ILogger<BreadboardValidator> logger)
             return;
         }
 
-        var cathode = anchor.Position + (orient == "left" ? -1 : 1);
+        var farPosition = anchor.Position + (orient == "left" ? -1 : 1);
         var min = anchor.Kind == "main" ? MainColumnMin : RailIndexMin;
         var max = anchor.Kind == "main" ? MainColumnMax : RailIndexMax;
 
-        if (cathode < min || cathode > max)
+        if (farPosition < min || farPosition > max)
         {
             errors.Add($"{path}.anchor", "footprint_off_board");
         }
     }
 
+    /// <summary>
+    /// A three-legged inline package (TO-92). Its legs run along one row of the main grid, one
+    /// column apart, so only "left" and "right" leave each leg in a strip of its own — a
+    /// vertical placement would put two legs in the same five-hole strip, and a power rail is
+    /// one continuous strip, which is why an anchor there is rejected outright.
+    /// </summary>
+    private static void ValidateInlinePackage(
+        JsonElement component,
+        string path,
+        int columnSpan,
+        HashSet<string> boardUids,
+        ErrorList errors)
+    {
+        var orient = ReadEnum(component, "orient", path, PackageOrientations, errors, required: true);
+        var anchor = ReadAnchor(component, path, boardUids, errors, required: true);
+
+        if (anchor is null || orient is null)
+        {
+            return;
+        }
+
+        if (anchor.Kind != "main")
+        {
+            errors.Add($"{path}.anchor.kind", "must_be_main");
+            return;
+        }
+
+        var lastColumn = anchor.Position + ((orient == "left" ? -1 : 1) * (columnSpan - 1));
+        if (lastColumn < MainColumnMin || lastColumn > MainColumnMax)
+        {
+            errors.Add($"{path}.anchor.col", "package_off_board");
+        }
+    }
+
     /// <summary>
     /// Packages that straddle the centre gap. Pin 1 sits in row "e" or "f" on the main grid
     /// and the package runs across <paramref name="columnSpan"/> columns: row "e" reads left

Media.JoshHeaps.Net/wwwroot/css/breadboard.css

@@ -39,6 +39,9 @@
     --bb-chip-pin: #c2c2c8;
     --bb-resistor-body: #d6c298;
     --bb-resistor-lead: #a9a9ad;
+    --bb-diode-body: #9aa7b4;
+    --bb-diode-band: #1c1c20;
+    --bb-transistor-body: #1f1f24;
     --bb-button-body: #34343a;
     --bb-button-cap: #c9553f;
     --bb-button-cap-down: #8d3a2b;
@@ -76,6 +79,7 @@
 
     --bb-wire-shadow: rgba(0, 0, 0, 0.22);
     --bb-chip-body: #2b2b30;
+    --bb-transistor-body: #2b2b30;
     --bb-supply-body: #26303a;
 }
 

Media.JoshHeaps.Net/wwwroot/js/breadboard/editor/component-art.js

@@ -167,6 +167,95 @@ function drawResistor(ctx, component, pins, colors, state, zoom) {
     ctx.restore();
 }
 
+function drawDiode(ctx, component, pins, colors) {
+    const [anode, cathode] = pins;
+    if (!anode || !cathode) return;
+
+    drawLead(ctx, anode, cathode, colors);
+
+    const angle = Math.atan2(cathode.y - anode.y, cathode.x - anode.x);
+    const length = Math.hypot(cathode.x - anode.x, cathode.y - anode.y);
+    const bodyLength = Math.max(PITCH * 0.5, Math.min(length * 0.6, PITCH * 1.8));
+    const bodyHeight = PITCH * 0.34;
+
+    ctx.save();
+    ctx.translate((anode.x + cathode.x) / 2, (anode.y + cathode.y) / 2);
+    ctx.rotate(angle);
+
+    ctx.fillStyle = colors.diodeBody;
+    roundRect(ctx, -bodyLength / 2, -bodyHeight / 2, bodyLength, bodyHeight, bodyHeight * 0.3);
+    ctx.fill();
+
+    // The band marks the cathode, which after the rotation is always the +x end.
+    ctx.fillStyle = colors.diodeBand;
+    ctx.fillRect(bodyLength * 0.24, -bodyHeight / 2, bodyLength * 0.16, bodyHeight);
+
+    ctx.restore();
+}
+
+/**
+ * TO-92 package seen from above: a flat face with a domed back, sitting over its own
+ * three holes. Everything is drawn within half a pitch of the pin row so the body stays
+ * inside componentBounds, which is what hit-testing and dirty-rect culling use.
+ */
+function drawTransistor(ctx, component, pins, colors, zoom) {
+    const placed = pins.filter(p => p !== null);
+    if (placed.length < 3) return;
+
+    const xs = placed.map(p => p.x);
+    const ys = placed.map(p => p.y);
+    const x = Math.min(...xs);
+    const y = Math.min(...ys);
+    const w = Math.max(...xs) - x;
+    const cy = y + (Math.max(...ys) - y) / 2;
+    const pad = PITCH * 0.34;
+    const left = x - pad;
+    const right = x + w + pad;
+    const flatY = cy + PITCH * 0.42;
+    const backY = cy - PITCH * 0.52;
+
+    ctx.strokeStyle = colors.chipPin;
+    ctx.lineWidth = PITCH * 0.12;
+    ctx.lineCap = 'butt';
+    for (const pin of placed) {
+        ctx.beginPath();
+        ctx.moveTo(pin.x, flatY - PITCH * 0.1);
+        ctx.lineTo(pin.x, flatY + PITCH * 0.16);
+        ctx.stroke();
+    }
+
+    ctx.fillStyle = colors.transistorBody;
+    ctx.beginPath();
+    ctx.moveTo(left, flatY);
+    ctx.lineTo(right, flatY);
+    ctx.lineTo(right, backY + PITCH * 0.22);
+    ctx.quadraticCurveTo((left + right) / 2, backY - PITCH * 0.28, left, backY + PITCH * 0.22);
+    ctx.closePath();
+    ctx.fill();
+
+    const def = getComponentDef(component.type);
+    ctx.fillStyle = colors.chipLabel;
+    ctx.textAlign = 'center';
+
+    if (zoom > 1.4) {
+        // Leg letters, taken from the registry's pin names so they can never disagree
+        // with the netlist. They follow the pins, so a rotated part reads correctly.
+        ctx.font = `${PITCH * 0.26}px system-ui, -apple-system, "Segoe UI", sans-serif`;
+        ctx.textBaseline = 'bottom';
+        ctx.globalAlpha = 0.7;
+        for (let i = 0; i < 3; i++) {
+            if (pins[i]) ctx.fillText(def.pins[i].name[0].toUpperCase(), pins[i].x, flatY - PITCH * 0.08);
+        }
+        ctx.globalAlpha = 1;
+    }
+
+    if (zoom > 0.9) {
+        ctx.font = `${PITCH * 0.3}px system-ui, -apple-system, "Segoe UI", sans-serif`;
+        ctx.textBaseline = 'middle';
+        ctx.fillText(def.label, (left + right) / 2, backY + PITCH * 0.3);
+    }
+}
+
 function drawPushButton(ctx, component, pins, colors, state) {
     const placed = pins.filter(p => p !== null);
     if (placed.length < 4) return;
@@ -387,6 +476,10 @@ export function drawComponent(ctx, component, boards, colors, state, zoom) {
     switch (component.type) {
         case 'led': drawLed(ctx, component, pins, colors, state); break;
         case 'resistor': drawResistor(ctx, component, pins, colors, state, zoom); break;
+        case 'diode': drawDiode(ctx, component, pins, colors); break;
+        case 'npn': case 'pnp': case 'nmos': case 'pmos':
+            drawTransistor(ctx, component, pins, colors, zoom);
+            break;
         case 'pushButton': drawPushButton(ctx, component, pins, colors, state); break;
         case 'dipSwitch8': drawDipSwitch(ctx, component, pins, colors, state, zoom); break;
         case 'powerSupply5V': drawPowerSupply(ctx, component, pins, colors, state, zoom, boards); break;

Media.JoshHeaps.Net/wwwroot/js/breadboard/editor/palette.js

@@ -7,9 +7,10 @@ import { el, button, createListenerBag } from './dom.js';
 import { COMPONENT_TYPES, getComponentDef } from '../shared/component-registry.js';
 import { WIRE_COLORS, DEFAULT_WIRE_COLOR } from '../shared/circuit-schema.js';
 
-const CATEGORY_ORDER = Object.freeze(['passive', 'output', 'input', 'power', 'chip']);
+const CATEGORY_ORDER = Object.freeze(['passive', 'semiconductor', 'output', 'input', 'power', 'chip']);
 const CATEGORY_LABELS = Object.freeze(Object.assign(Object.create(null), {
     passive: 'Passive',
+    semiconductor: 'Semiconductor',
     output: 'Output',
     input: 'Input',
     power: 'Power',

Media.JoshHeaps.Net/wwwroot/js/breadboard/editor/status.js

@@ -27,6 +27,8 @@ const WARNING_LABELS = Object.freeze(Object.assign(Object.create(null), {
     unknownComponent: 'Unrecognised component',
     unconnectedSupply: 'Supply is not connected to anything',
     selfShorted: 'Both ends are on the same net',
+    floatingControl: 'Nothing is connected to the base or gate',
+    unlimitedBaseCurrent: 'Transistor base has no series resistor',
     engineError: 'The simulation engine hit an internal error',
     warningsSuppressed: 'Some warnings were coalesced'
 }));
@@ -39,7 +41,8 @@ const SEVERITY = Object.freeze(Object.assign(Object.create(null), {
     shortCircuit: 'error',
     contention: 'error',
     oscillation: 'warn',
-    ledOvercurrent: 'warn'
+    ledOvercurrent: 'warn',
+    unlimitedBaseCurrent: 'warn'
 }));
 
 function humanizeKind(kind) {

Media.JoshHeaps.Net/wwwroot/js/breadboard/editor/theme-colors.js

@@ -34,6 +34,9 @@ const TOKENS = Object.freeze({
     chipPin: ['--bb-chip-pin', '#c8c8cc'],
     resistorBody: ['--bb-resistor-body', '#d8c49a'],
     resistorLead: ['--bb-resistor-lead', '#b0b0b0'],
+    diodeBody: ['--bb-diode-body', '#9aa7b4'],
+    diodeBand: ['--bb-diode-band', '#1c1c20'],
+    transistorBody: ['--bb-transistor-body', '#1f1f24'],
     buttonBody: ['--bb-button-body', '#3a3a3e'],
     buttonCap: ['--bb-button-cap', '#c9553f'],
     buttonCapDown: ['--bb-button-cap-down', '#8d3a2b'],

Media.JoshHeaps.Net/wwwroot/js/breadboard/engine/models/conduction.js

@@ -0,0 +1,49 @@
+/**
+ * Bidirectional conduction between two pins of one component.
+ *
+ * Shared by every element that opens and closes a channel: mechanical contacts
+ * (push button, DIP switch) and the transistors. Conduction is NOT a dynamic
+ * merge of the two nets — re-running union-find every time a contact moves
+ * would be slow, and it would invalidate the net index the UI is handed once at
+ * load. Each side simply drives the other with what it sees.
+ *
+ * Conduction preserves STRENGTH, unlike a resistor: a closed contact between
+ * the two power rails has to hand SUPPLY strength across so the short reads as
+ * a short circuit and not as garden-variety contention. The same is true of a
+ * saturated transistor, which is why it destroys itself in real life.
+ *
+ * The source net is always read EXCLUDING the element's own contribution to it,
+ * or a closed channel would read back the value it is itself asserting and
+ * latch onto it forever after the real source went away.
+ *
+ * Every caller passes a non-zero delay. It is a loop breaker rather than a
+ * physical figure: two elements wired in a ring would otherwise conduct round
+ * it at zero delay forever and trip the delta-cycle guard.
+ */
+
+import { STRENGTH_HIGHZ, VALUE_LOW } from '../constants.js';
+import { driveStrength, driveMask, MASK_LOW, MASK_HIGH } from '../drive.js';
+
+/** Passes `fromPin`'s net through to `toPin` at full strength, or opens the channel. */
+export function conduct(ctx, inst, fromPin, toPin, closed, delayNs) {
+	if (!closed) {
+		ctx.drive(inst, toPin, STRENGTH_HIGHZ, VALUE_LOW, delayNs);
+		return;
+	}
+	const drive = ctx.driveExcludingSelf(inst, fromPin);
+	const strength = driveStrength(drive);
+	const mask = driveMask(drive);
+	// A source that is itself unresolved (both polarities present) passes
+	// nothing: there is no single value to conduct.
+	if (strength === STRENGTH_HIGHZ || (mask !== MASK_LOW && mask !== MASK_HIGH)) {
+		ctx.drive(inst, toPin, STRENGTH_HIGHZ, VALUE_LOW, delayNs);
+		return;
+	}
+	ctx.drive(inst, toPin, strength, mask === MASK_HIGH ? 1 : 0, delayNs);
+}
+
+/** Refreshes both directions of the bridge between `a` and `b`. */
+export function refreshBridge(ctx, inst, a, b, closed, delayNs) {
+	conduct(ctx, inst, a, b, closed, delayNs);
+	conduct(ctx, inst, b, a, closed, delayNs);
+}

Media.JoshHeaps.Net/wwwroot/js/breadboard/engine/models/diode.js

@@ -0,0 +1,62 @@
+/**
+ * Diode. Pin 1 is the anode, pin 2 the banded cathode.
+ *
+ * A one-way conductor: forward biased it passes the anode's drive through to
+ * the cathode at full strength (conduction.js), reverse biased it passes
+ * nothing, and it NEVER drives its anode in either state. That asymmetry is the
+ * whole part — it is what makes diode-OR steering, polarity protection and a
+ * freewheel path across an inductive load behave differently from a wire.
+ *
+ * Forward bias is decided from the cathode read EXCLUDING this diode's own
+ * contribution, for the same reason the transistors do it: a diode charging an
+ * otherwise-floating node would otherwise see the node it had just pulled high,
+ * conclude it was no longer forward biased, release, and oscillate.
+ *
+ * The cathode is treated as blocking whenever it is ALREADY high — not only
+ * when it is driven high by something stronger. Two supplies steered into one
+ * node through a diode each is the ordinary case, and neither diode should
+ * report conducting into the other's output.
+ *
+ * LIMIT OF THIS MODEL. There is no forward voltage drop, because there is no
+ * voltage between 0 V and 5 V to drop it to (see resistor.js). A diode here is
+ * a switch that only closes one way; a chain of them does not stack up 0.7 V a
+ * time, and a diode cannot be used as a voltage reference. Reverse breakdown is
+ * not modelled either, so a Zener cannot be built from one. Forward voltage
+ * DOES matter for an LED, and lives in the LED's own model.
+ */
+
+import { LEVEL_HIGH, LEVEL_WEAK_HIGH } from '../constants.js';
+import { defineModel } from './registry.js';
+import { conduct } from './conduction.js';
+
+/** Loop breaker, as everywhere else conduction is instantaneous in reality. */
+const DIODE_DELAY_NS = 1;
+
+const PIN_ANODE = 0;
+const PIN_CATHODE = 1;
+
+function isHigh(level) {
+	return level === LEVEL_HIGH || level === LEVEL_WEAK_HIGH;
+}
+
+function refreshBias(ctx, inst) {
+	// The anode needs no exclusion: a diode never drives its own anode, so its
+	// driver there is high-Z and contributes nothing to exclude.
+	const forward = isHigh(ctx.level(inst, PIN_ANODE)) && !isHigh(ctx.levelExcludingSelf(inst, PIN_CATHODE));
+	conduct(ctx, inst, PIN_ANODE, PIN_CATHODE, forward, DIODE_DELAY_NS);
+}
+
+defineModel({
+	type: 'diode',
+	pinCount: 2,
+	delayNs: DIODE_DELAY_NS,
+	functionalPins: [[1, 2]],
+
+	init(ctx, inst) {
+		refreshBias(ctx, inst);
+	},
+
+	evaluate(ctx, inst) {
+		refreshBias(ctx, inst);
+	},
+});

Media.JoshHeaps.Net/wwwroot/js/breadboard/engine/models/index.js

@@ -11,5 +11,7 @@ import './supply.js';
 import './resistor.js';
 import './switches.js';
 import './led.js';
+import './diode.js';
+import './transistor.js';
 
 export { registry, getModel, knownTypes, defineModel, WAKE_INIT, WAKE_PIN, WAKE_TIMER } from './registry.js';

Media.JoshHeaps.Net/wwwroot/js/breadboard/engine/models/switches.js

@@ -1,50 +1,22 @@
 /**
  * Mechanical contacts: push button and 8-position DIP switch.
  *
- * A closed contact is modelled as a bidirectional conductor rather than a
+ * Both are pure conduction elements — see conduction.js for why a closed
- * dynamic merge of the two nets. Re-running union-find every time a user
+ * contact drives across rather than merging the two nets, and why it preserves
- * presses a button would be both slow and a nightmare for the UI's net index,
+ * drive strength while doing so.
- * which is handed out once at load and must stay valid.
- *
- * Conduction preserves STRENGTH, unlike a resistor: a closed button between the
- * two power rails has to hand SUPPLY strength across so the short reads as a
- * short circuit and not as garden-variety contention.
  *
  * The 1 ns contact delay is a loop breaker, not a debounce model. Two contacts
  * wired in a ring would otherwise conduct round it at zero delay forever.
  */
 
-import { STRENGTH_HIGHZ, VALUE_LOW } from '../constants.js';
-import { driveStrength, driveMask, MASK_LOW, MASK_HIGH } from '../drive.js';
 import { defineModel, WAKE_PIN } from './registry.js';
+import { refreshBridge } from './conduction.js';
 
 const CONTACT_DELAY_NS = 1;
 
-/**
+/** Closes or opens the contact bridging `a` and `b`. */
- * Passes `fromPin`'s net through to `toPin` at full strength, or opens the
+function setContact(ctx, inst, a, b, closed) {
- * contact. Reads the source net excluding this element's own contribution, so
+	refreshBridge(ctx, inst, a, b, closed, CONTACT_DELAY_NS);
- * the contact cannot latch onto the value it is itself asserting.
- */
-function conduct(ctx, inst, fromPin, toPin, closed) {
-	if (!closed) {
-		ctx.drive(inst, toPin, STRENGTH_HIGHZ, VALUE_LOW, CONTACT_DELAY_NS);
-		return;
-	}
-	const drive = ctx.driveExcludingSelf(inst, fromPin);
-	const strength = driveStrength(drive);
-	const mask = driveMask(drive);
-	// A source that is itself unresolved (both polarities present) passes
-	// nothing: there is no single value to conduct.
-	if (strength === STRENGTH_HIGHZ || (mask !== MASK_LOW && mask !== MASK_HIGH)) {
-		ctx.drive(inst, toPin, STRENGTH_HIGHZ, VALUE_LOW, CONTACT_DELAY_NS);
-		return;
-	}
-	ctx.drive(inst, toPin, strength, mask === MASK_HIGH ? 1 : 0, CONTACT_DELAY_NS);
-}
-
-function refreshContact(ctx, inst, a, b, closed) {
-	conduct(ctx, inst, a, b, closed);
-	conduct(ctx, inst, b, a, closed);
 }
 
 /* ------------------------------------------------------------------ *
@@ -70,12 +42,12 @@ defineModel({
 	},
 
 	init(ctx, inst) {
-		refreshContact(ctx, inst, BUTTON_A, BUTTON_B, inst.state.pressed);
+		setContact(ctx, inst, BUTTON_A, BUTTON_B, inst.state.pressed);
 	},
 
 	evaluate(ctx, inst, wake) {
 		if (wake.reason === WAKE_PIN && wake.pin !== BUTTON_A && wake.pin !== BUTTON_B) return;
-		refreshContact(ctx, inst, BUTTON_A, BUTTON_B, inst.state.pressed);
+		setContact(ctx, inst, BUTTON_A, BUTTON_B, inst.state.pressed);
 	},
 
 	/** `{ type:"input", uid, value }` — value is a boolean: pressed or released. */
@@ -83,7 +55,7 @@ defineModel({
 		const pressed = value === true || value?.pressed === true;
 		if (inst.state.pressed === pressed) return;
 		inst.state.pressed = pressed;
-		refreshContact(ctx, inst, BUTTON_A, BUTTON_B, pressed);
+		setContact(ctx, inst, BUTTON_A, BUTTON_B, pressed);
 	},
 });
 
@@ -116,7 +88,7 @@ defineModel({
 	init(ctx, inst) {
 		for (let k = 1; k <= DIP_SWITCH_COUNT; k++) {
 			const [a, b] = dipPins(k);
-			refreshContact(ctx, inst, a, b, inst.state.on[k - 1] === 1);
+			setContact(ctx, inst, a, b, inst.state.on[k - 1] === 1);
 		}
 	},
 
@@ -129,7 +101,7 @@ defineModel({
 		if (wake.reason !== WAKE_PIN) {
 			for (let k = 1; k <= DIP_SWITCH_COUNT; k++) {
 				const [a, b] = dipPins(k);
-				refreshContact(ctx, inst, a, b, inst.state.on[k - 1] === 1);
+				setContact(ctx, inst, a, b, inst.state.on[k - 1] === 1);
 			}
 			return;
 		}
@@ -138,7 +110,7 @@ defineModel({
 		if (!(pin >= 0) || pin > 15) return;
 		const k = pin < DIP_SWITCH_COUNT ? pin + 1 : 16 - pin;
 		const [a, b] = dipPins(k);
-		refreshContact(ctx, inst, a, b, inst.state.on[k - 1] === 1);
+		setContact(ctx, inst, a, b, inst.state.on[k - 1] === 1);
 	},
 
 	/**
@@ -152,6 +124,6 @@ defineModel({
 		if (inst.state.on[k - 1] === on) return;
 		inst.state.on[k - 1] = on;
 		const [a, b] = dipPins(k);
-		refreshContact(ctx, inst, a, b, on === 1);
+		setContact(ctx, inst, a, b, on === 1);
 	},
 });

Media.JoshHeaps.Net/wwwroot/js/breadboard/engine/models/transistor.js

@@ -0,0 +1,158 @@
+/**
+ * Transistors: NPN and PNP bipolars, N- and P-channel MOSFETs.
+ *
+ * All four are the same device to this engine — a channel between pin 1 and
+ * pin 3 that the control pin on pin 2 opens and closes — so they share one
+ * definition factory and differ only in the polarity of the turn-on test and in
+ * which mistakes are worth warning about. Pin order is the physical TO-92 one,
+ * control terminal in the middle: emitter/base/collector, source/gate/drain.
+ *
+ * Turning on takes BOTH terminals into account, never the control pin alone. An
+ * NPN conducts when its base is above its emitter, so an NPN whose emitter is
+ * already sitting on the 5 V rail stays off no matter what its base does — the
+ * single most common reason a beginner's high-side switch does nothing.
+ *
+ * The channel terminal is read EXCLUDING this device's own contribution, and
+ * that is load-bearing rather than defensive. An emitter follower pulls its own
+ * emitter up to what it is switching; read plainly, the device would then see
+ * base and emitter at the same level, decide Vbe had collapsed, turn off, drop
+ * the emitter, turn on again, and oscillate forever at the switching delay. The
+ * exclusion asks the question that actually decides conduction: would current
+ * flow if this device were not already conducting?
+ *
+ * WHAT THIS MODEL IS NOT. There is no linear region and no gain: the device is
+ * saturated or cut off, nothing between. There is no Vbe and no Vce(sat), so a
+ * follower's output does not sit 0.7 V below its base — the engine has no
+ * voltage between 0 and 5 V to put it at (see resistor.js). And the control pin
+ * is a pure high-Z input drawing no base current, which is exactly why the
+ * unlimited-base warning below has to exist: the model cannot punish a missing
+ * base resistor by melting, so it says so instead. A MOSFET's intrinsic body
+ * diode is not modelled either, so an off device never conducts backwards.
+ *
+ * A conducting device passes drive strength through unchanged (conduction.js),
+ * so a transistor wired collector-to-rail and emitter-to-ground still reports
+ * the short circuit it would really be.
+ */
+
+import { LEVEL_HIGH, LEVEL_WEAK_HIGH, LEVEL_LOW, LEVEL_WEAK_LOW, NO_NET, STRENGTH_SUPPLY } from '../constants.js';
+import { driveStrength } from '../drive.js';
+import { defineModel } from './registry.js';
+import { refreshBridge } from './conduction.js';
+
+/**
+ * Switching delay, ns. Slower than a contact bridging two nets because a real
+ * transistor's storage and rise time genuinely dominate it, and comfortably
+ * non-zero so a discrete inverter ring oscillates at a rate rather than
+ * tripping the delta-cycle guard.
+ */
+const SWITCHING_DELAY_NS = 10;
+
+const PIN_CHANNEL_LOW = 0; // emitter / source
+const PIN_CONTROL = 1; // base / gate
+const PIN_CHANNEL_HIGH = 2; // collector / drain
+
+function isHigh(level) {
+	return level === LEVEL_HIGH || level === LEVEL_WEAK_HIGH;
+}
+
+function isLow(level) {
+	return level === LEVEL_LOW || level === LEVEL_WEAK_LOW;
+}
+
+/**
+ * Whether the channel is open. A floating control pin reads as neither high nor
+ * low and therefore leaves the device off, which is the right answer for a
+ * bipolar (no base current, no conduction) and the safe one for a MOSFET, whose
+ * real gate would drift somewhere unpredictable — hence the load-time warning.
+ */
+function isConducting(ctx, inst) {
+	const control = ctx.level(inst, PIN_CONTROL);
+	const channel = ctx.levelExcludingSelf(inst, PIN_CHANNEL_LOW);
+	return inst.model.pChannel ? isLow(control) && isHigh(channel) : isHigh(control) && isLow(channel);
+}
+
+function refreshChannel(ctx, inst) {
+	const conducting = isConducting(ctx, inst);
+	refreshBridge(ctx, inst, PIN_CHANNEL_LOW, PIN_CHANNEL_HIGH, conducting, SWITCHING_DELAY_NS);
+	return conducting;
+}
+
+/** A control pin nothing else touches can never switch the device. */
+function warnIfControlFloating(ctx, inst) {
+	const net = ctx.netOf(inst, PIN_CONTROL);
+	if (net !== NO_NET && ctx.netListenerCount(net) > 1) return;
+	ctx.staticWarning(
+		'floatingControl',
+		`${inst.type} ${inst.uid}: nothing is connected to its ${inst.model.controlName}, so it can never switch on`,
+		[inst.uid],
+	);
+}
+
+/**
+ * Base current is what destroys a bipolar driven straight from a logic output,
+ * and this engine draws none — so the mistake is reported the first time the
+ * device actually conducts with an unlimited base rather than at load, where a
+ * base deliberately tied to ground to hold the part off would trip it too.
+ * Latched per instance: a transistor switching at 1 MHz must not re-warn.
+ *
+ * Evidence of a base resistor is a resistor touching the base's net, which is
+ * the same dominant-resistance approximation the LED uses and inherits the same
+ * blind spot — a resistor on that net need not be in series with the base. The
+ * one place that approximation is not merely imprecise but WRONG is a base
+ * clipped straight onto a power rail: every part on the board shares its rails,
+ * so a rail nearly always carries some resistor, yet nothing is in series with
+ * a base sitting on it. Supply drive strength is exactly what identifies that
+ * case, so it is tested first and overrides the resistor evidence.
+ *
+ * The result errs one way only: it can stay quiet about a real mistake, and
+ * never invents one.
+ */
+function warnIfBaseUnlimited(ctx, inst) {
+	if (inst.state.warnedBaseDrive) return;
+	const net = ctx.netOf(inst, PIN_CONTROL);
+	if (net === NO_NET) return;
+	const onSupplyRail = driveStrength(ctx.driveExcludingSelf(inst, PIN_CONTROL)) === STRENGTH_SUPPLY;
+	if (!onSupplyRail && ctx.dominantSeriesOhms(net) > 0) return;
+	inst.state.warnedBaseDrive = true;
+	ctx.warn(
+		'unlimitedBaseCurrent',
+		[inst.uid],
+		net,
+		`${inst.type} ${inst.uid} is switched on through a base with no series resistor; a real one would draw destructive base current`,
+	);
+}
+
+function defineTransistor(definition) {
+	defineModel({
+		pinCount: 3,
+		delayNs: SWITCHING_DELAY_NS,
+		// The two channel terminals must reach different nets for the device to
+		// switch anything; the control pin may legitimately share a net with
+		// either (a gate tied to its source is simply held off).
+		functionalPins: [[1, 3]],
+
+		createState() {
+			return { warnedBaseDrive: false };
+		},
+
+		init(ctx, inst) {
+			warnIfControlFloating(ctx, inst);
+			refreshChannel(ctx, inst);
+		},
+
+		evaluate(ctx, inst) {
+			// Any pin can change the answer: the control pin decides drive, the
+			// channel-low pin decides whether there is a potential to drive it
+			// with, and the channel-high pin changes what gets passed across.
+			const conducting = refreshChannel(ctx, inst);
+			if (conducting && inst.model.bipolar) warnIfBaseUnlimited(ctx, inst);
+		},
+
+		...definition,
+	});
+}
+
+defineTransistor({ type: 'npn', pChannel: false, bipolar: true, controlName: 'base' });
+defineTransistor({ type: 'pnp', pChannel: true, bipolar: true, controlName: 'base' });
+defineTransistor({ type: 'nmos', pChannel: false, bipolar: false, controlName: 'gate' });
+defineTransistor({ type: 'pmos', pChannel: true, bipolar: false, controlName: 'gate' });

Media.JoshHeaps.Net/wwwroot/js/breadboard/shared/component-registry.js

@@ -116,6 +116,52 @@ function chipDef(type) {
     };
 }
 
+/**
+ * Orientations a three-legged inline package may carry. Its legs run along a row, so
+ * only the two horizontal directions leave each leg in a strip of its own: a column's
+ * rows a-e are one strip, which would short two legs of any vertical placement.
+ */
+export const INLINE_ORIENTATIONS = Object.freeze(['left', 'right']);
+
+/** Footprint for a part whose pins step away from the anchor in the orient direction. */
+function orientStepFootprint(pinCount) {
+    const pins = [];
+    for (let pin = 1; pin <= pinCount; pin++) {
+        pins.push(pin === 1
+            ? Object.freeze({ pin, at: 'anchor' })
+            : Object.freeze({ pin, at: 'orientStep', steps: pin - 1 }));
+    }
+    return Object.freeze({ kind: 'orientStep', pinCount, pins: Object.freeze(pins) });
+}
+
+/**
+ * The four transistors differ only in polarity and in what their legs are called; the
+ * package, the footprint and the placement rules are one part. Pin order is the
+ * physical TO-92 one, control terminal in the middle.
+ */
+function transistorDef(type, label, description, pinNames) {
+    return {
+        type,
+        label,
+        description,
+        category: 'semiconductor',
+        pins: namedPins(pinNames),
+        bodyColumns: 3,
+        straddlesGap: false,
+        anchorRows: null,
+        // A power rail is one continuous strip, so all three legs there would be common.
+        anchorKinds: Object.freeze(['main']),
+        anchorless: false,
+        orientable: true,
+        orientValues: INLINE_ORIENTATIONS,
+        defaultOrient: 'right',
+        dipStyle: false,
+        footprint: orientStepFootprint(3),
+        defaultProps: Object.freeze({}),
+        propSpecs: Object.freeze({})
+    };
+}
+
 const DEFS = Object.create(null);
 
 function define(def) {
@@ -186,6 +232,45 @@ define({
     })
 });
 
+define({
+    type: 'diode',
+    label: 'Diode',
+    description: 'Signal diode (1N4148). Anchor is the anode; the banded cathode sits one hole away. Passes current one way only.',
+    category: 'semiconductor',
+    pins: namedPins(['anode', 'cathode']),
+    bodyColumns: 1,
+    straddlesGap: false,
+    anchorRows: null,
+    anchorKinds: Object.freeze(['main', 'rail']),
+    anchorless: false,
+    orientable: true,
+    orientValues: Object.freeze(['up', 'down', 'left', 'right']),
+    // Same reasoning as the LED: 'right' is the only default that reaches a different
+    // strip from every main column and also works from a rail hole.
+    defaultOrient: 'right',
+    dipStyle: false,
+    footprint: orientStepFootprint(2),
+    defaultProps: Object.freeze({}),
+    propSpecs: Object.freeze({})
+});
+
+const TRANSISTOR_DEFS = Object.freeze([
+    transistorDef('npn', 'NPN',
+        'NPN transistor (2N3904): emitter, base, collector. Conducts when the base is high and the emitter is the low side, so it switches a load to ground.',
+        ['emitter', 'base', 'collector']),
+    transistorDef('pnp', 'PNP',
+        'PNP transistor (2N3906): emitter, base, collector. Conducts when the base is low and the emitter is the high side, so it switches a load to the supply.',
+        ['emitter', 'base', 'collector']),
+    transistorDef('nmos', 'N-MOSFET',
+        'N-channel MOSFET (2N7000): source, gate, drain. Conducts when the gate is high and the source is the low side. The gate draws no current, so it needs a pull-down to stay off.',
+        ['source', 'gate', 'drain']),
+    transistorDef('pmos', 'P-MOSFET',
+        'P-channel MOSFET (BS250): source, gate, drain. Conducts when the gate is low and the source is the high side. The gate draws no current, so it needs a pull-up to stay off.',
+        ['source', 'gate', 'drain'])
+]);
+
+for (const def of TRANSISTOR_DEFS) define(def);
+
 define({
     type: 'pushButton',
     label: 'Push button',
@@ -277,7 +362,8 @@ Object.freeze(DEFS);
 
 /** All registered component type names, in palette order. */
 export const COMPONENT_TYPES = Object.freeze([
-    'led', 'resistor', 'pushButton', 'dipSwitch8', 'powerSupply5V', ...CHIP_TYPES
+    'led', 'resistor', 'diode', ...TRANSISTOR_DEFS.map(d => d.type),
+    'pushButton', 'dipSwitch8', 'powerSupply5V', ...CHIP_TYPES
 ]);
 
 /** Valid `orient` values for orientable components. */