diff --git a/.gitignore b/.gitignore
index f024b50..a965e14 100644
--- a/.gitignore
+++ b/.gitignore
@@ -9,3 +9,4 @@ ThermistorTable.h
 Makefile
 sim
 doc
+datalog.out
diff --git a/simulator/data_recorder.c b/simulator/data_recorder.c
new file mode 100644
index 0000000..b181dc9
--- /dev/null
+++ b/simulator/data_recorder.c
@@ -0,0 +1,56 @@
+/*
+ * data_recorder.c
+ *
+ * Record simulator data to a file in real-time.
+ *
+ */
+
+#include "simulator.h"
+#include "data_recorder.h"
+#include <stdio.h>
+#include <time.h>
+
+static FILE *file;
+
+#define MAX_PINS 100
+static uint32_t values[MAX_PINS];      ///< Pin and value states
+static int pin_count;                  ///< Number of pins we emit
+
+void recorder_init(const char* filename) {
+  sim_assert( ! file, "Recorder already initialized");
+
+  file = fopen(filename, "w");
+  sim_assert(file, "record_init: failed to create file");
+
+  time_t t = time(NULL);
+  fprintf(file, "; Teacup_Firmware simulator data log on %s\n",
+          asctime(localtime(&t)));
+  fflush(file);
+}
+
+void add_trace_var(const char* name, int pin) {
+  sim_assert(file, "add_trace_var: Recorder not initialized");
+  sim_assert(pin < MAX_PINS, "pin number invalid");
+
+  fprintf(file, "; %d - %s\n", pin, name);
+  if (pin >= pin_count)
+    pin_count = pin + 1;
+  fflush(file);
+}
+
+// Record a binary signal change
+void record_pin(int pin, bool state, uint32_t t) {
+  if (state == values[pin]) return;
+
+  sim_assert(file , "record_pin: Recorder not initialized");
+  sim_assert(pin < MAX_PINS, "pin number invalid");
+
+  values[pin] = state;
+
+  // Naive format: each line contains all values, beginning with the time
+  fprintf(file, "%u", t);
+  for (int i = 0; i < pin_count; i++)
+    fprintf(file, "\t%u", values[i]);
+  fprintf(file, "\n");
+  fflush(file);
+}
diff --git a/simulator/data_recorder.h b/simulator/data_recorder.h
new file mode 100644
index 0000000..cf20acf
--- /dev/null
+++ b/simulator/data_recorder.h
@@ -0,0 +1,12 @@
+/*
+ * data_recorder.h
+ */
+
+#ifndef DATA_RECORDER_H_
+#define DATA_RECORDER_H_
+
+void recorder_init(const char* filename);
+void record_pin(int pin, bool state, uint32_t time);
+void add_trace_var(const char* name, int pin);
+
+#endif /* DATA_RECORDER_H_ */
diff --git a/simulator/simulator.c b/simulator/simulator.c
index f9b07c7..e476985 100644
--- a/simulator/simulator.c
+++ b/simulator/simulator.c
@@ -3,6 +3,7 @@
 #include <stdarg.h>
 
 #include "simulator.h"
+#include "data_recorder.h"
 
 uint8_t ACSR;
 uint8_t TIMSK1;
@@ -35,6 +36,33 @@ void sim_start(int argc, char** argv) {
   // Save these for the serial_init code
   g_argc = argc;
   g_argv = argv;
+
+  recorder_init("datalog.out");
+
+  // Record pin names in datalog
+#define NAME_PIN(x) add_trace_var(#x , x);
+  NAME_PIN(X_STEP_PIN);
+  NAME_PIN(X_DIR_PIN);
+  NAME_PIN(X_MIN_PIN);
+  NAME_PIN(X_ENABLE_PIN);
+  NAME_PIN(Y_STEP_PIN);
+  NAME_PIN(Y_DIR_PIN);
+  NAME_PIN(Y_MIN_PIN);
+  NAME_PIN(Y_ENABLE_PIN);
+  NAME_PIN(Z_STEP_PIN);
+  NAME_PIN(Z_DIR_PIN);
+  NAME_PIN(Z_MIN_PIN);
+  NAME_PIN(Z_ENABLE_PIN);
+  NAME_PIN(E_STEP_PIN);
+  NAME_PIN(E_DIR_PIN);
+  NAME_PIN(E_ENABLE_PIN);
+
+  NAME_PIN(STEPPER_ENABLE_PIN);
+
+  NAME_PIN(SCK);
+  NAME_PIN(MOSI);
+  NAME_PIN(MISO);
+  NAME_PIN(SS);
 }
 
 /* -- debugging ------------------------------------------------------------ */
@@ -129,6 +157,8 @@ void WRITE(pin_t pin, bool s) {
   }
 
   if (old_state != s) {
+    uint32_t useconds = 0;  // TODO
+    record_pin(pin, s, useconds);
     #ifdef TRACE_ALL_PINS
       fgreen();
       for (int i = 0; i < PIN_NB; i++) {