diff --git a/VFDStandalone/VFDStandalone.ino b/VFDStandalone/VFDStandalone.ino
new file mode 100644
index 0000000..d79218e
--- /dev/null
+++ b/VFDStandalone/VFDStandalone.ino
@@ -0,0 +1,342 @@
+// Arduino Mega 2560 + HV5812P VFD driver
+//
+// Tube wiring:
+// - HVOut1..HVOut7  -> digit segments A..G
+// - HVOut8          -> decimal point segment on the indicator grid
+// - HVOut9          -> alarm bell segment on the indicator grid
+// - HVOut10..HVOut13 -> digits 1..4
+// - HVOut14         -> indicator grid between digits 2 and 3
+//
+// Send an integer over the USB serial port and it will be shown on the VFD.
+// Examples:
+//   42<newline>
+//   -17<newline>
+//   1234.<newline>   // enables the decimal point
+//   1234!<newline>   // enables the alarm bell
+//   1234.!<newline>  // enables both
+
+#include <Arduino.h>
+
+namespace {
+
+constexpr uint8_t kHvDataPin = 51;   // MOSI on Mega 2560
+constexpr uint8_t kHvClockPin = 52;  // SCK on Mega 2560
+constexpr uint8_t kHvLatchPin = 53;  // User-configurable latch/strobe pin
+constexpr int8_t kHvBlankPin = 49;   // Set to -1 if BL/OE is not connected
+constexpr bool kBlankActiveHigh = true;
+
+constexpr unsigned long kSerialBaud = 115200;
+constexpr unsigned long kDigitHoldMicros = 2000;
+
+constexpr uint8_t kDigitCount = 4;
+constexpr uint8_t kSegmentCount = 7;
+constexpr uint8_t kDriverBits = 20;
+
+constexpr uint8_t kSegmentStartBit = 0;  // HVOut1 -> bit 0
+constexpr uint8_t kPointSegmentBit = 7;  // HVOut8 -> bit 7
+constexpr uint8_t kBellSegmentBit = 8;   // HVOut9 -> bit 8
+constexpr uint8_t kGridStartBit = 9;     // HVOut10 -> bit 9
+constexpr uint8_t kIndicatorGridBit = 13;  // HVOut14 -> bit 13
+
+char g_displayBuffer[kDigitCount] = {' ', ' ', ' ', ' '};
+char g_inputBuffer[16];
+uint8_t g_inputLength = 0;
+bool g_pointEnabled = false;
+bool g_bellEnabled = false;
+uint8_t g_rawOutput = 0;
+
+// Seven-segment encoding order is A, B, C, D, E, F, G.
+uint8_t encodeCharacter(char c) {
+  switch (c) {
+    case '0': return 0b0111111;
+    case '1': return 0b0000110;
+    case '2': return 0b1011011;
+    case '3': return 0b1001111;
+    case '4': return 0b1100110;
+    case '5': return 0b1101101;
+    case '6': return 0b1111101;
+    case '7': return 0b0000111;
+    case '8': return 0b1111111;
+    case '9': return 0b1101111;
+    case 'A':
+    case 'a': return 0b1110111;
+    case 'B':
+    case 'b': return 0b1111100;
+    case 'C':
+    case 'c': return 0b0111001;
+    case 'D':
+    case 'd': return 0b1011110;
+    case 'E':
+    case 'e': return 0b1111001;
+    case 'F':
+    case 'f': return 0b1110001;
+    case '-': return 0b1000000;
+    default: return 0;
+  }
+}
+
+void shiftDriverWord(uint32_t word) {
+  digitalWrite(kHvLatchPin, HIGH);
+  digitalWrite(kHvClockPin, HIGH);
+
+  for (int8_t bit = kDriverBits - 1; bit >= 0; --bit) {
+    digitalWrite(kHvDataPin, (word >> bit) & 0x1U ? HIGH : LOW);
+    digitalWrite(kHvClockPin, LOW);
+    digitalWrite(kHvClockPin, HIGH);
+  }
+
+  digitalWrite(kHvLatchPin, LOW);
+  digitalWrite(kHvLatchPin, HIGH);
+}
+
+void setDisplayBlanked(bool blanked) {
+  if (kHvBlankPin < 0) {
+    return;
+  }
+
+  const bool level = kBlankActiveHigh ? blanked : !blanked;
+  digitalWrite(kHvBlankPin, level ? HIGH : LOW);
+}
+
+void blankDisplay() {
+  shiftDriverWord(0);
+}
+
+uint32_t maskForHvOutput(uint8_t hvOutput) {
+  if (hvOutput == 0 || hvOutput > kDriverBits) {
+    return 0;
+  }
+
+  return 1UL << (hvOutput - 1);
+}
+
+void renderDigit(uint8_t digitIndex) {
+  uint32_t word = 0;
+  const uint8_t segments = encodeCharacter(g_displayBuffer[digitIndex]);
+
+  for (uint8_t segment = 0; segment < kSegmentCount; ++segment) {
+    if ((segments >> segment) & 0x1U) {
+      word |= (1UL << (kSegmentStartBit + segment));
+    }
+  }
+
+  word |= (1UL << (kGridStartBit + digitIndex));
+  shiftDriverWord(word);
+}
+
+void renderIndicator() {
+  uint32_t word = 1UL << kIndicatorGridBit;
+
+  if (g_pointEnabled) {
+    word |= 1UL << kPointSegmentBit;
+  }
+
+  if (g_bellEnabled) {
+    word |= 1UL << kBellSegmentBit;
+  }
+
+  shiftDriverWord(word);
+}
+
+void writeTextToDisplay(const char* text) {
+  for (uint8_t i = 0; i < kDigitCount; ++i) {
+    g_displayBuffer[i] = ' ';
+  }
+
+  size_t len = strlen(text);
+  if (len > kDigitCount) {
+    text += len - kDigitCount;
+    len = kDigitCount;
+  }
+
+  const uint8_t start = kDigitCount - len;
+  for (uint8_t i = 0; i < len; ++i) {
+    g_displayBuffer[start + i] = text[i];
+  }
+}
+
+void setDisplayFromNumber(long value) {
+  char buffer[16];
+  ltoa(value, buffer, 10);
+  writeTextToDisplay(buffer);
+}
+
+bool parseDisplayCommand(const char* input,
+                         char* displayText,
+                         size_t displayTextSize,
+                         bool& pointEnabled,
+                         bool& bellEnabled) {
+  size_t inputIndex = 0;
+  size_t displayIndex = 0;
+
+  if (input[inputIndex] == '-') {
+    if (displayIndex + 1 >= displayTextSize) {
+      return false;
+    }
+    displayText[displayIndex++] = input[inputIndex++];
+  }
+
+  const size_t digitStart = inputIndex;
+  while (isxdigit(static_cast<unsigned char>(input[inputIndex]))) {
+    if (displayIndex + 1 >= displayTextSize) {
+      return false;
+    }
+    displayText[displayIndex] = toupper(static_cast<unsigned char>(input[inputIndex]));
+    ++displayIndex;
+    ++inputIndex;
+  }
+
+  if (inputIndex == digitStart) {
+    return false;
+  }
+
+  pointEnabled = false;
+  bellEnabled = false;
+
+  while (input[inputIndex] != '\0') {
+    if (input[inputIndex] == '.') {
+      pointEnabled = true;
+    } else if (input[inputIndex] == '!') {
+      bellEnabled = true;
+    } else {
+      return false;
+    }
+    ++inputIndex;
+  }
+
+  displayText[displayIndex] = '\0';
+  return true;
+}
+
+bool parseRawOutputCommand(const char* input, uint8_t& hvOutput) {
+  if (strncmp(input, "RAW ", 4) != 0) {
+    return false;
+  }
+
+  char* endPtr = nullptr;
+  const long parsed = strtol(input + 4, &endPtr, 10);
+  if (*endPtr != '\0' || parsed < 0 || parsed > kDriverBits) {
+    return false;
+  }
+
+  hvOutput = static_cast<uint8_t>(parsed);
+  return true;
+}
+
+void commitSerialBuffer() {
+  if (g_inputLength == 0) {
+    return;
+  }
+
+  g_inputBuffer[g_inputLength] = '\0';
+
+  uint8_t rawOutput = 0;
+  if (parseRawOutputCommand(g_inputBuffer, rawOutput)) {
+    g_rawOutput = rawOutput;
+    if (g_rawOutput == 0) {
+      Serial.println(F("RAW mode OFF"));
+    } else {
+      Serial.print(F("RAW mode: HVOUT"));
+      Serial.println(g_rawOutput);
+    }
+    g_inputLength = 0;
+    return;
+  }
+
+  char displayText[16];
+  bool pointEnabled = false;
+  bool bellEnabled = false;
+  if (parseDisplayCommand(g_inputBuffer, displayText, sizeof(displayText), pointEnabled, bellEnabled)) {
+    g_rawOutput = 0;
+    writeTextToDisplay(displayText);
+    g_pointEnabled = pointEnabled;
+    g_bellEnabled = bellEnabled;
+    Serial.print(F("Displaying: "));
+    Serial.println(displayText);
+    Serial.print(F("Point: "));
+    Serial.println(g_pointEnabled ? F("ON") : F("OFF"));
+    Serial.print(F("Bell: "));
+    Serial.println(g_bellEnabled ? F("ON") : F("OFF"));
+  } else {
+    Serial.print(F("Ignored invalid input: "));
+    Serial.println(g_inputBuffer);
+  }
+
+  g_inputLength = 0;
+}
+
+void pollSerial() {
+  while (Serial.available() > 0) {
+    const char incoming = static_cast<char>(Serial.read());
+
+    if (incoming == '\r' || incoming == '\n') {
+      commitSerialBuffer();
+      continue;
+    }
+
+    if (incoming == '\b' || incoming == 127) {
+      if (g_inputLength > 0) {
+        --g_inputLength;
+      }
+      continue;
+    }
+
+    if (g_inputLength < sizeof(g_inputBuffer) - 1) {
+      g_inputBuffer[g_inputLength++] = incoming;
+    }
+  }
+}
+
+void refreshDisplay() {
+  if (g_rawOutput != 0) {
+    setDisplayBlanked(true);
+    shiftDriverWord(maskForHvOutput(g_rawOutput));
+    setDisplayBlanked(false);
+    delayMicroseconds(kDigitHoldMicros);
+    return;
+  }
+
+  static uint8_t currentPhase = 0;
+
+  setDisplayBlanked(true);
+  if (currentPhase < kDigitCount) {
+    renderDigit(currentPhase);
+  } else if (g_pointEnabled || g_bellEnabled) {
+    renderIndicator();
+  } else {
+    blankDisplay();
+  }
+  setDisplayBlanked(false);
+  delayMicroseconds(kDigitHoldMicros);
+  setDisplayBlanked(true);
+
+  currentPhase = (currentPhase + 1) % (kDigitCount + 1);
+}
+
+}  // namespace
+
+void setup() {
+  pinMode(kHvDataPin, OUTPUT);
+  pinMode(kHvClockPin, OUTPUT);
+  pinMode(kHvLatchPin, OUTPUT);
+  if (kHvBlankPin >= 0) {
+    pinMode(kHvBlankPin, OUTPUT);
+  }
+
+  digitalWrite(kHvDataPin, LOW);
+  digitalWrite(kHvClockPin, HIGH);
+  digitalWrite(kHvLatchPin, HIGH);
+  setDisplayBlanked(true);
+
+  Serial.begin(kSerialBaud);
+  writeTextToDisplay("0");
+  blankDisplay();
+
+  Serial.println(F("HV5812P VFD controller ready."));
+  Serial.println(F("Send an integer followed by newline."));
+}
+
+void loop() {
+  pollSerial();
+  refreshDisplay();
+}