diff --git a/Gaugecontroller/Gaugecontroller.ino b/Gaugecontroller/Gaugecontroller.ino
index 8ff7d50..e84be18 100644
--- a/Gaugecontroller/Gaugecontroller.ino
+++ b/Gaugecontroller/Gaugecontroller.ino
@@ -36,8 +36,6 @@ char displayBuffer[kDigitCount] = {' ', ' ', ' ', ' '};
 bool pointEnabled = false;
 bool bellEnabled = false;
 uint8_t currentPhase = 0;
-unsigned long phaseStartMicros = 0;
-bool phaseActive = false;
 
 uint8_t encodeCharacter(char c) {
   switch (c) {
@@ -112,12 +110,12 @@ void clear() {
   bellEnabled = false;
 }
 
-bool parseCommand(const char* command) {
+bool parseCommand(const String& command) {
   char displayText[16];
   size_t inputIndex = 0;
   size_t displayIndex = 0;
 
-  if (command[0] == '\0') {
+  if (command.length() == 0) {
     return false;
   }
 
@@ -129,7 +127,7 @@ bool parseCommand(const char* command) {
   }
 
   const size_t digitStart = inputIndex;
-  while (command[inputIndex] != '\0' &&
+  while (inputIndex < static_cast<size_t>(command.length()) &&
          isxdigit(static_cast<unsigned char>(command[inputIndex]))) {
     if (displayIndex + 1 >= sizeof(displayText)) {
       return false;
@@ -144,7 +142,7 @@ bool parseCommand(const char* command) {
 
   bool newPointEnabled = false;
   bool newBellEnabled = false;
-  while (command[inputIndex] != '\0') {
+  while (inputIndex < static_cast<size_t>(command.length())) {
     if (command[inputIndex] == '.') {
       newPointEnabled = true;
     } else if (command[inputIndex] == '!') {
@@ -203,19 +201,8 @@ void begin() {
   shiftDriverWord(0);
 }
 
-// Non-blocking. Returns immediately while the current digit is still being held;
-// only does work when the hold time has elapsed and it is time to advance phases.
 void refresh() {
-  unsigned long now = micros();
-  if (phaseActive && (now - phaseStartMicros) < kDigitHoldMicros) {
-    return;
-  }
-
   setBlanked(true);
-  if (phaseActive) {
-    currentPhase = (currentPhase + 1) % (kDigitCount + 1);
-  }
-
   if (currentPhase < kDigitCount) {
     renderDigit(currentPhase);
   } else if (pointEnabled || bellEnabled) {
@@ -224,9 +211,10 @@ void refresh() {
     shiftDriverWord(0);
   }
   setBlanked(false);
+  delayMicroseconds(kDigitHoldMicros);
+  setBlanked(true);
 
-  phaseStartMicros = micros();
-  phaseActive = true;
+  currentPhase = (currentPhase + 1) % (kDigitCount + 1);
 }
 
 }  // namespace vfd
@@ -292,10 +280,6 @@ struct Gauge {
 
   bool sweepEnabled = false;
   bool sweepTowardMax = true;
-
-  // Cached direction-pin state. 0 = uninitialised, 1 = forward, -1 = reverse.
-  // Lets setDir() skip redundant digitalWrites when the direction hasn't flipped.
-  int8_t lastDir = 0;
 };
 
 enum LedFx : uint8_t { FX_BLINK = 0, FX_BREATHE = 1, FX_DFLASH = 2 };
@@ -314,26 +298,29 @@ struct BlinkState {
 };
 
 Gauge gauges[GAUGE_COUNT];
-
-// Fixed receive buffer — Arduino String would heap-fragment on the Mega over time.
-// kRxBufSize - 1 is the max payload (one byte reserved for the null terminator).
-static const uint8_t kRxBufSize = 128;
-char rxBuf[kRxBufSize];
-uint8_t rxLen = 0;
+String rxLine;
 
 CRGB leds[TOTAL_LEDS];
 uint8_t gaugeLedOffset[GAUGE_COUNT];
 uint8_t gaugeLedCount[GAUGE_COUNT];
 BlinkState blinkState[TOTAL_LEDS];
-// Precomputed in setup() from gaugePins[].ledOrder so per-LED writes don't
-// have to walk the gauge table on every call.
-bool ledNeedsSwap[TOTAL_LEDS];
 bool ledsDirty = false;
 
 // FastLED drives the shared strip as RGB. Each gauge's ledOrder string marks per-LED
 // type ('R' = RGB, 'G' = GRB); writes to GRB-ordered LEDs pre-swap R and G to compensate.
+inline bool ledNeedsRgSwap(uint8_t globalIdx) {
+  for (uint8_t i = 0; i < GAUGE_COUNT; i++) {
+    uint8_t off = gaugeLedOffset[i];
+    if (globalIdx >= off && globalIdx < off + gaugeLedCount[i]) {
+      char c = gaugePins[i].ledOrder[globalIdx - off];
+      return c == 'G' || c == 'g';
+    }
+  }
+  return false;
+}
+
 inline CRGB encodeForStrip(uint8_t globalIdx, CRGB color) {
-  if (ledNeedsSwap[globalIdx]) {
+  if (ledNeedsRgSwap(globalIdx)) {
     uint8_t tmp = color.r;
     color.r = color.g;
     color.g = tmp;
@@ -351,9 +338,6 @@ inline CRGB readLed(uint8_t globalIdx) {
 
 // Sends one-line command replies back over the control port.
 //
-// All parse* functions take a null-terminated char* (no Arduino String) so the
-// command pipeline never touches the heap.
-//
 // Serial protocol summary.
 //
 // Host -> controller commands (newline-terminated ASCII):
@@ -370,7 +354,7 @@ inline CRGB readLed(uint8_t globalIdx) {
 //   LED <id> <idx|a-b> <r> <g> <b>
 //   BLINK <id> <idx|a-b> <on_ms> <off_ms> [<r> <g> <b>]
 //   BREATHE <id> <idx|a-b> <period_ms> <r> <g> <b>
-//   DFLASH <id> <idx|a-b> <r> <g> <b>
+//   DFLASH <id> <idx|a-b> <r> <ig> <b>
 //   VFD <text[.!]>
 //   PING
 //
@@ -404,10 +388,15 @@ inline CRGB readLed(uint8_t globalIdx) {
 //     Emitted once per configured LED before the trailing OK reply to LED?.
 //   HOMED <id>
 //     Debug event printed on DEBUG_PORT when a homing sequence settles successfully.
-void sendReply(const char* s) {
+void sendReply(const String& s) {
   CMD_PORT.println(s);
 }
 
+// Tiny float absolute-value helper to avoid dragging more machinery into the sketch.
+float absf(float x) {
+  return (x < 0.0f) ? -x : x;
+}
+
 // Updates the cached enable state and toggles the hardware pin if one exists.
 void setEnable(uint8_t id, bool en) {
   if (id >= GAUGE_COUNT) return;
@@ -421,19 +410,9 @@ void setEnable(uint8_t id, bool en) {
 }
 
 // Applies the logical direction after accounting for per-gauge inversion.
-// digitalWrite is skipped when the direction is already correct, which is the
-// common case (a step run almost always reuses the previous direction).
 void setDir(uint8_t id, bool forward) {
-  Gauge& g = gauges[id];
-  int8_t want = forward ? 1 : -1;
-  if (g.lastDir == want) return;
-  g.lastDir = want;
-
   bool level = gaugePins[id].dirInverted ? !forward : forward;
   digitalWrite(gaugePins[id].dirPin, level ? HIGH : LOW);
-  // DIR-to-STEP setup time. Most A4988/DRV8825-class drivers want at least
-  // ~200 ns; 1 us is cheap insurance and only paid when the direction flips.
-  delayMicroseconds(1);
 }
 
 // Emits one step pulse with the polarity expected by the driver.
@@ -542,13 +521,13 @@ void updateSweepTarget(uint8_t id) {
 
   if (g.sweepTowardMax) {
     g.targetPos = g.maxPos;
-    if (g.currentPos >= g.maxPos && fabsf(g.velocity) < 1.0f) {
+    if (g.currentPos >= g.maxPos && absf(g.velocity) < 1.0f) {
       g.sweepTowardMax = false;
       g.targetPos = g.minPos;
     }
   } else {
     g.targetPos = g.minPos;
-    if (g.currentPos <= g.minPos && fabsf(g.velocity) < 1.0f) {
+    if (g.currentPos <= g.minPos && absf(g.velocity) < 1.0f) {
       g.sweepTowardMax = true;
       g.targetPos = g.maxPos;
     }
@@ -583,7 +562,7 @@ void updateGauge(uint8_t id) {
 
   long error = g.targetPos - g.currentPos;
 
-  if (error == 0 && fabsf(g.velocity) < 0.01f) {
+  if (error == 0 && absf(g.velocity) < 0.01f) {
     g.velocity = 0.0f;
     g.stepAccumulator = 0.0f;
     return;
@@ -591,8 +570,7 @@ void updateGauge(uint8_t id) {
 
   float dir = (error > 0) ? 1.0f : (error < 0 ? -1.0f : 0.0f);
   // Basic trapezoidal profile: brake if the remaining travel is shorter than the stop distance.
-  // parseAccel rejects accel <= 0, so the divisor is always positive.
-  float brakingDistance = (g.velocity * g.velocity) / (2.0f * g.accel);
+  float brakingDistance = (g.velocity * g.velocity) / (2.0f * g.accel + 0.0001f);
 
   if ((float)labs(error) <= brakingDistance) {
     if (g.velocity > 0.0f) {
@@ -656,10 +634,10 @@ void updateGauge(uint8_t id) {
 
 // Parses `SET <id> <pos>` and updates the target position.
 // Replies: `OK`, `ERR BAD_ID`.
-bool parseSet(const char* line) {
+bool parseSet(const String& line) {
   int id;
   long pos;
-  if (sscanf(line, "SET %d %ld", &id, &pos) == 2) {
+  if (sscanf(line.c_str(), "SET %d %ld", &id, &pos) == 2) {
     if (id < 0 || id >= GAUGE_COUNT) {
       sendReply("ERR BAD_ID");
       return true;
@@ -677,15 +655,14 @@ bool parseSet(const char* line) {
 
 // Parses `SPEED <id> <speed>` and updates the max step rate.
 // Replies: `OK`, `ERR BAD_ID`, `ERR BAD_SPEED`.
-// AVR libc sscanf doesn't support %f by default, so we hand-split with strchr/atof.
-bool parseSpeed(const char* line) {
-  if (strncmp(line, "SPEED ", 6) != 0) return false;
-  const char* p = line + 6;
-  const char* sp = strchr(p, ' ');
-  if (!sp) return false;
+bool parseSpeed(const String& line) {
+  int firstSpace = line.indexOf(' ');
+  int secondSpace = line.indexOf(' ', firstSpace + 1);
+  if (firstSpace < 0 || secondSpace < 0) return false;
+  if (line.substring(0, firstSpace) != "SPEED") return false;
 
-  int id = atoi(p);
-  float speed = atof(sp + 1);
+  int id = line.substring(firstSpace + 1, secondSpace).toInt();
+  float speed = line.substring(secondSpace + 1).toFloat();
 
   if (id < 0 || id >= GAUGE_COUNT) {
     sendReply("ERR BAD_ID");
@@ -703,14 +680,14 @@ bool parseSpeed(const char* line) {
 
 // Parses `ACCEL <id> <accel>` and updates the acceleration limit.
 // Replies: `OK`, `ERR BAD_ID`, `ERR BAD_ACCEL`.
-bool parseAccel(const char* line) {
-  if (strncmp(line, "ACCEL ", 6) != 0) return false;
-  const char* p = line + 6;
-  const char* sp = strchr(p, ' ');
-  if (!sp) return false;
+bool parseAccel(const String& line) {
+  int firstSpace = line.indexOf(' ');
+  int secondSpace = line.indexOf(' ', firstSpace + 1);
+  if (firstSpace < 0 || secondSpace < 0) return false;
+  if (line.substring(0, firstSpace) != "ACCEL") return false;
 
-  int id = atoi(p);
-  float accel = atof(sp + 1);
+  int id = line.substring(firstSpace + 1, secondSpace).toInt();
+  float accel = line.substring(secondSpace + 1).toFloat();
 
   if (id < 0 || id >= GAUGE_COUNT) {
     sendReply("ERR BAD_ID");
@@ -728,9 +705,9 @@ bool parseAccel(const char* line) {
 
 // Parses `ENABLE <id> <0|1>` and toggles the selected driver.
 // Replies: `OK`, `ERR BAD_ID`.
-bool parseEnable(const char* line) {
+bool parseEnable(const String& line) {
   int id, en;
-  if (sscanf(line, "ENABLE %d %d", &id, &en) == 2) {
+  if (sscanf(line.c_str(), "ENABLE %d %d", &id, &en) == 2) {
     if (id < 0 || id >= GAUGE_COUNT) {
       sendReply("ERR BAD_ID");
       return true;
@@ -745,9 +722,9 @@ bool parseEnable(const char* line) {
 
 // Parses `ZERO <id>` and declares the current position to be home.
 // Replies: `OK`, `ERR BAD_ID`.
-bool parseZero(const char* line) {
+bool parseZero(const String& line) {
   int id;
-  if (sscanf(line, "ZERO %d", &id) == 1) {
+  if (sscanf(line.c_str(), "ZERO %d", &id) == 1) {
     if (id < 0 || id >= GAUGE_COUNT) {
       sendReply("ERR BAD_ID");
       return true;
@@ -768,9 +745,9 @@ bool parseZero(const char* line) {
 
 // Parses `HOME <id>` or `HOMEALL` and kicks off the homing sequence.
 // Replies: `OK`, `ERR BAD_ID`. Successful completion later emits debug line `HOMED <id>`.
-bool parseHome(const char* line) {
+bool parseHome(const String& line) {
   int id;
-  if (sscanf(line, "HOME %d", &id) == 1) {
+  if (sscanf(line.c_str(), "HOME %d", &id) == 1) {
     if (id < 0 || id >= GAUGE_COUNT) {
       sendReply("ERR BAD_ID");
       return true;
@@ -781,7 +758,7 @@ bool parseHome(const char* line) {
     return true;
   }
 
-  if (strcmp(line, "HOMEALL") == 0) {
+  if (line == "HOMEALL") {
     requestHomeAll();
     sendReply("OK");
     return true;
@@ -792,17 +769,17 @@ bool parseHome(const char* line) {
 
 // Parses `SWEEP <id> <accel> <speed>` and enables or disables end-to-end motion.
 // Replies: `OK`, `ERR BAD_ID`.
-bool parseSweep(const char* line) {
-  if (strncmp(line, "SWEEP ", 6) != 0) return false;
-  const char* p = line + 6;
-  const char* sp1 = strchr(p, ' ');
-  if (!sp1) return false;
-  const char* sp2 = strchr(sp1 + 1, ' ');
-  if (!sp2) return false;
+bool parseSweep(const String& line) {
+  int firstSpace = line.indexOf(' ');
+  int secondSpace = line.indexOf(' ', firstSpace + 1);
+  int thirdSpace = line.indexOf(' ', secondSpace + 1);
 
-  int id = atoi(p);
-  float accel = atof(sp1 + 1);
-  float speed = atof(sp2 + 1);
+  if (firstSpace < 0 || secondSpace < 0 || thirdSpace < 0) return false;
+  if (line.substring(0, firstSpace) != "SWEEP") return false;
+
+  int id = line.substring(firstSpace + 1, secondSpace).toInt();
+  float accel = line.substring(secondSpace + 1, thirdSpace).toFloat();
+  float speed = line.substring(thirdSpace + 1).toFloat();
 
   if (id < 0 || id >= GAUGE_COUNT) {
     sendReply("ERR BAD_ID");
@@ -831,8 +808,8 @@ bool parseSweep(const char* line) {
 // Answers `POS?` with current motion state for every gauge.
 // Emits one `POS <id> <cur> <tgt> <homed> <homingState> <sweep>` line per gauge,
 // then replies `OK`.
-bool parsePosQuery(const char* line) {
-  if (strcmp(line, "POS?") == 0) {
+bool parsePosQuery(const String& line) {
+  if (line == "POS?") {
     for (uint8_t i = 0; i < GAUGE_COUNT; i++) {
       CMD_PORT.print("POS ");
       CMD_PORT.print(i);
@@ -855,8 +832,8 @@ bool parsePosQuery(const char* line) {
 
 // Answers `CFG?` with speed and acceleration for every gauge.
 // Emits one `CFG <id> <maxSpeed> <accel>` line per gauge, then replies `OK`.
-bool parseCfgQuery(const char* line) {
-  if (strcmp(line, "CFG?") == 0) {
+bool parseCfgQuery(const String& line) {
+  if (line == "CFG?") {
     for (uint8_t i = 0; i < GAUGE_COUNT; i++) {
       CMD_PORT.print("CFG ");
       CMD_PORT.print(i);
@@ -873,8 +850,8 @@ bool parseCfgQuery(const char* line) {
 
 // Answers the mandatory life question: are you there?
 // Reply: `PONG`.
-bool parsePing(const char* line) {
-  if (strcmp(line, "PING") == 0) {
+bool parsePing(const String& line) {
+  if (line == "PING") {
     sendReply("PONG");
     return true;
   }
@@ -883,17 +860,17 @@ bool parsePing(const char* line) {
 
 // Parses `VFD <text>` where <text> is up to four hex characters with optional `.` and `!` suffixes.
 // Replies: `OK`, `ERR BAD_VFD`.
-bool parseVfd(const char* line) {
-  if (strcmp(line, "VFD") == 0) {
+bool parseVfd(const String& line) {
+  if (line == "VFD") {
     vfd::clear();
     sendReply("OK");
     return true;
   }
 
-  if (strncmp(line, "VFD ", 4) != 0) return false;
+  if (!line.startsWith("VFD ")) return false;
 
-  const char* payload = line + 4;
-  if (*payload == '\0') {
+  const String payload = line.substring(4);
+  if (payload.length() == 0) {
     vfd::clear();
     sendReply("OK");
     return true;
@@ -909,8 +886,8 @@ bool parseVfd(const char* line) {
 
 // Answers `LED?` with the current RGB values for every configured LED.
 // Emits one `LED <id> <idx> <r> <g> <b>` line per configured LED, then replies `OK`.
-bool parseLedQuery(const char* line) {
-  if (strcmp(line, "LED?") == 0) {
+bool parseLedQuery(const String& line) {
+  if (line == "LED?") {
     for (uint8_t i = 0; i < GAUGE_COUNT; i++) {
       for (uint8_t j = 0; j < gaugeLedCount[i]; j++) {
         CRGB c = readLed(gaugeLedOffset[i] + j);
@@ -934,10 +911,10 @@ bool parseLedQuery(const char* line) {
 
 // Parses `LED <id> <idx|a-b> <r> <g> <b>` and writes static colours.
 // Replies: `OK`, `ERR BAD_ID`, `ERR BAD_IDX`.
-bool parseLed(const char* line) {
+bool parseLed(const String& line) {
   int id, r, g, b;
   char idxToken[16];
-  if (sscanf(line, "LED %d %15s %d %d %d", &id, idxToken, &r, &g, &b) == 5) {
+  if (sscanf(line.c_str(), "LED %d %15s %d %d %d", &id, idxToken, &r, &g, &b) == 5) {
     if (id < 0 || id >= GAUGE_COUNT) { sendReply("ERR BAD_ID"); return true; }
     char* dash = strchr(idxToken, '-');
     int idxFirst = atoi(idxToken);
@@ -959,11 +936,11 @@ bool parseLed(const char* line) {
 
 // Parses `BLINK ...` and assigns a simple on/off effect to one LED or a range.
 // Replies: `OK`, `ERR BAD_ID`, `ERR BAD_IDX`, `ERR BAD_TIME`.
-bool parseBlink(const char* line) {
+bool parseBlink(const String& line) {
   int id, onMs, offMs, r, g, b;
   char idxToken[16];
   // Optional RGB values let BLINK either reuse or replace the current colour.
-  int count = sscanf(line, "BLINK %d %15s %d %d %d %d %d",
+  int count = sscanf(line.c_str(), "BLINK %d %15s %d %d %d %d %d",
                      &id, idxToken, &onMs, &offMs, &r, &g, &b);
   if (count != 4 && count != 7) return false;
 
@@ -1007,10 +984,10 @@ bool parseBlink(const char* line) {
 
 // Parses `BREATHE ...` and assigns a triangle-wave fade effect.
 // Replies: `OK`, `ERR BAD_ID`, `ERR BAD_IDX`, `ERR BAD_TIME`.
-bool parseBreathe(const char* line) {
+bool parseBreathe(const String& line) {
   int id, periodMs, r, g, b;
   char idxToken[16];
-  if (sscanf(line, "BREATHE %d %15s %d %d %d %d",
+  if (sscanf(line.c_str(), "BREATHE %d %15s %d %d %d %d",
              &id, idxToken, &periodMs, &r, &g, &b) != 6) return false;
   if (id < 0 || id >= GAUGE_COUNT) { sendReply("ERR BAD_ID"); return true; }
   char* dash = strchr(idxToken, '-');
@@ -1040,10 +1017,10 @@ bool parseBreathe(const char* line) {
 
 // Parses `DFLASH ...` and assigns the double-flash pattern.
 // Replies: `OK`, `ERR BAD_ID`, `ERR BAD_IDX`.
-bool parseDflash(const char* line) {
+bool parseDflash(const String& line) {
   int id, r, g, b;
   char idxToken[16];
-  if (sscanf(line, "DFLASH %d %15s %d %d %d",
+  if (sscanf(line.c_str(), "DFLASH %d %15s %d %d %d",
              &id, idxToken, &r, &g, &b) != 5) return false;
   if (id < 0 || id >= GAUGE_COUNT) { sendReply("ERR BAD_ID"); return true; }
   char* dash = strchr(idxToken, '-');
@@ -1127,7 +1104,7 @@ void updateBlink() {
 
 // Runs the command parsers in order until one claims the line.
 // Reply: `ERR BAD_CMD` when no parser accepts the line.
-void processLine(const char* line) {
+void processLine(const String& line) {
   if (parseSet(line)) return;
   if (parseSpeed(line)) return;
   if (parseAccel(line)) return;
@@ -1155,24 +1132,16 @@ void readCommands() {
     char c = (char)CMD_PORT.read();
 
     if (c == '\n') {
-      // Trim trailing whitespace.
-      while (rxLen > 0 && (rxBuf[rxLen - 1] == ' ' || rxBuf[rxLen - 1] == '\t')) {
-        rxLen--;
+      rxLine.trim();
+      if (rxLine.length() > 0) {
+        processLine(rxLine);
       }
-      rxBuf[rxLen] = '\0';
-      // Skip leading whitespace.
-      char* start = rxBuf;
-      while (*start == ' ' || *start == '\t') start++;
-      if (*start) {
-        processLine(start);
-      }
-      rxLen = 0;
+      rxLine = "";
     } else if (c != '\r') {
-      if (rxLen >= kRxBufSize - 1) {
-        rxLen = 0;
+      rxLine += c;
+      if (rxLine.length() > 120) {
+        rxLine = "";
         sendReply("ERR TOO_LONG");
-      } else {
-        rxBuf[rxLen++] = c;
       }
     }
   }
@@ -1199,17 +1168,11 @@ void setup() {
     gauges[i].lastUpdateMicros = micros();
   }
 
-  // Flatten the per-gauge LED counts into offsets on the shared strip,
-  // and precompute the GRB-vs-RGB swap flag so writeLed/readLed don't have
-  // to walk the gauge table on every call.
+  // Flatten the per-gauge LED counts into offsets on the shared strip.
   uint8_t ledOff = 0;
   for (uint8_t i = 0; i < GAUGE_COUNT; i++) {
     gaugeLedCount[i] = cstrLen(gaugePins[i].ledOrder);
     gaugeLedOffset[i] = ledOff;
-    for (uint8_t j = 0; j < gaugeLedCount[i]; j++) {
-      char c = gaugePins[i].ledOrder[j];
-      ledNeedsSwap[ledOff + j] = (c == 'G' || c == 'g');
-    }
     ledOff += gaugeLedCount[i];
   }
   FastLED.addLeds<WS2812B, LED_DATA_PIN, RGB>(leds, TOTAL_LEDS);