diff --git a/README.md b/README.md
index 4263b42..f6eb110 100644
--- a/README.md
+++ b/README.md
@@ -74,7 +74,8 @@ dokumentation, forbindelser og biblioteker beskrives ved den enkelte sketch.
 
 ### Arduino UNO R4 Minima
 
-- [Sketch-område](sketches/arduino-uno-r4-minima) – klar til kommende Minima-sketches
+- [`sos_blink`](sketches/arduino-uno-r4-minima/sos_blink) – SOS i morsekode på
+  den indbyggede LED
 
 ## Tilføjelse af flere boards
 
diff --git a/boards/arduino-uno-r4-minima/README.md b/boards/arduino-uno-r4-minima/README.md
index ba253f0..bde3339 100644
--- a/boards/arduino-uno-r4-minima/README.md
+++ b/boards/arduino-uno-r4-minima/README.md
@@ -67,8 +67,8 @@ interne temperatursensor måler primært chiptemperaturen.
 
 ## Sketches i dette repo
 
-Der er endnu ingen Minima-specifikke sketches. Nye sketches placeres under
-[`sketches/arduino-uno-r4-minima`](../../sketches/arduino-uno-r4-minima).
+- [`sos_blink`](../../sketches/arduino-uno-r4-minima/sos_blink) – blinker SOS i
+  morsekode med den indbyggede LED
 
 ## Kilder
 
diff --git a/sketches/arduino-uno-r4-minima/README.md b/sketches/arduino-uno-r4-minima/README.md
index f9537e2..2f28b67 100644
--- a/sketches/arduino-uno-r4-minima/README.md
+++ b/sketches/arduino-uno-r4-minima/README.md
@@ -1,14 +1,18 @@
 # Sketches til Arduino UNO R4 Minima
 
-Der er endnu ingen Minima-specifikke sketches i projektet.
+## Tilgængelige sketches
+
+- [`sos_blink`](sos_blink) – blinker SOS i morsekode med den indbyggede LED
+
+## Struktur
 
 Hver ny sketch skal placeres i sin egen mappe, hvor mappen og `.ino`-filen har
 samme navn:
 
 ```text
 sketches/arduino-uno-r4-minima/
-  blink/
-    blink.ino
+  sos_blink/
+    sos_blink.ino
 ```
 
 Kompilér med:
diff --git a/sketches/arduino-uno-r4-minima/sos_blink/README.md b/sketches/arduino-uno-r4-minima/sos_blink/README.md
new file mode 100644
index 0000000..7d84f04
--- /dev/null
+++ b/sketches/arduino-uno-r4-minima/sos_blink/README.md
@@ -0,0 +1,25 @@
+# SOS Blink
+
+Blinker `SOS` (`... --- ...`) i morsekode med den indbyggede LED på D13 på
+Arduino UNO R4 Minima. Der kræves ingen eksterne komponenter.
+
+En tidsenhed er 200 ms:
+
+- prik: 1 enhed tændt
+- streg: 3 enheder tændt
+- mellemrum mellem signaler: 1 enhed
+- mellemrum mellem bogstaver: 3 enheder
+- mellemrum mellem gentagelser: 7 enheder
+
+## Kompilering
+
+```powershell
+arduino-cli compile --fqbn arduino:renesas_uno:minima sketches/arduino-uno-r4-minima/sos_blink
+```
+
+## Upload
+
+```powershell
+arduino-cli upload --port COM7 --fqbn arduino:renesas_uno:minima sketches/arduino-uno-r4-minima/sos_blink
+```
+
diff --git a/sketches/arduino-uno-r4-minima/sos_blink/sos_blink.ino b/sketches/arduino-uno-r4-minima/sos_blink/sos_blink.ino
new file mode 100644
index 0000000..435a189
--- /dev/null
+++ b/sketches/arduino-uno-r4-minima/sos_blink/sos_blink.ino
@@ -0,0 +1,46 @@
+// SOS in Morse code on the Arduino UNO R4 Minima built-in LED.
+// S = ...  O = ---  S = ...
+
+constexpr unsigned long UNIT_MS = 200;
+
+void blinkSymbol(unsigned long onUnits) {
+  digitalWrite(LED_BUILTIN, HIGH);
+  delay(onUnits * UNIT_MS);
+  digitalWrite(LED_BUILTIN, LOW);
+
+  // Every Morse symbol is followed by a one-unit gap.
+  delay(UNIT_MS);
+}
+
+void blinkLetter(const char *pattern) {
+  for (const char *symbol = pattern; *symbol != '\0'; ++symbol) {
+    blinkSymbol(*symbol == '.' ? 1 : 3);
+  }
+}
+
+void letterGap() {
+  // blinkSymbol() already supplied the first of the three gap units.
+  delay(2 * UNIT_MS);
+}
+
+void wordGap() {
+  // blinkSymbol() already supplied the first of the seven gap units.
+  delay(6 * UNIT_MS);
+}
+
+void setup() {
+  pinMode(LED_BUILTIN, OUTPUT);
+  digitalWrite(LED_BUILTIN, LOW);
+}
+
+void loop() {
+  blinkLetter("...");
+  letterGap();
+
+  blinkLetter("---");
+  letterGap();
+
+  blinkLetter("...");
+  wordGap();
+}
+