diff --git a/arduino/msaqsg/ch04/Telegraph/telegraph.cpp b/arduino/msaqsg/ch04/Telegraph/telegraph.cpp
index a5fd161..9eccfc8 100644
--- a/arduino/msaqsg/ch04/Telegraph/telegraph.cpp
+++ b/arduino/msaqsg/ch04/Telegraph/telegraph.cpp
@@ -44,3 +44,62 @@ const char* DIGITS[] = {
     "---..", // 8
     "----.", // 9
 };
+
+Telegraph::Telegraph(const int output_pin, const int dit_length) {
+    _output_pin = output_pin;
+    _dit_length = dit_length;
+    _dah_length = dit_length * 3;
+    pinMode(_output_pin, OUTPUT);
+}
+
+void Telegraph::output_code(const char* code) {
+    const unsigned int code_length = strlen(code);
+
+    for (unsigned int i = 0; i < code_length; i++) {
+        if (code[i] == '.') {
+            dit();
+        } else {
+            dah();
+        }
+
+        if (i != code_length - 1) {
+            delay(_dit_length);
+        }
+    }
+}
+
+void Telegraph::dit() {
+    Serial.print(".");
+    output_symbol(_dit_length);
+}
+
+void Telegraph::dah() {
+    Serial.print("-");
+    output_symbol(_dah_length);
+}
+
+void Telegraph::output_symbol(const int length) {
+    digitalWrite(_output_pin, HIGH);
+    delay(length);
+    digitalWrite(_output_pin, LOW);
+}
+
+void Telegraph::send_message(const char* message) {
+    unsigned int message_length = (unsigned int)strlen(message);
+    for (unsigned int i = 0; i < message_length; i++) {
+        const char current_char = toupper(message[i]);
+
+        if (isalpha(current_char)) {
+            output_code(LETTERS[current_char - 'A']);
+            delay(_dah_length);
+        } else if (isdigit(current_char)) {
+            output_code(DIGITS[current_char - '0']);
+            delay(_dah_length);
+        } else if (current_char == ' ') {
+            Serial.print(" ");
+            delay(_dit_length * 7);
+        }
+    }
+
+    Serial.println();
+}