diff --git a/internal_filesystem/lib/mpos/audio/duplex_test.py b/internal_filesystem/lib/mpos/audio/duplex_test.py
new file mode 100644
index 00000000..601a68fa
--- /dev/null
+++ b/internal_filesystem/lib/mpos/audio/duplex_test.py
@@ -0,0 +1,102 @@
+"""Minimal duplex I2S proof-of-concept for Fri3d 2024.
+
+Creates TX + RX I2S instances simultaneously using merged pin config
+from the fri3d_2024 board setup. Intended for quick validation only.
+"""
+
+import time
+
+try:
+    import machine
+    _HAS_MACHINE = True
+except ImportError:
+    _HAS_MACHINE = False
+
+
+# Merged pin map from internal_filesystem/lib/mpos/board/fri3d_2024.py
+I2S_PINS = {
+    "ws": 47,       # shared LRCLK
+    "sck": 2,       # DAC bit clock
+    "sd": 16,       # DAC data out
+    "sck_in": 17,   # mic bit clock
+    "sd_in": 15,    # mic data in
+}
+
+
+class DuplexI2STest:
+    """Minimal duplex setup: one TX I2S + one RX I2S running together."""
+
+    def __init__(self, sample_rate=16000, duration_ms=3000):
+        self.sample_rate = sample_rate
+        self.duration_ms = duration_ms
+        self._tx = None
+        self._rx = None
+
+    def _init_i2s(self):
+        if not _HAS_MACHINE:
+            raise RuntimeError("machine.I2S not available")
+
+        self._tx = machine.I2S(
+            0,
+            sck=machine.Pin(I2S_PINS["sck"], machine.Pin.OUT),
+            ws=machine.Pin(I2S_PINS["ws"], machine.Pin.OUT),
+            sd=machine.Pin(I2S_PINS["sd"], machine.Pin.OUT),
+            mode=machine.I2S.TX,
+            bits=16,
+            format=machine.I2S.MONO,
+            rate=self.sample_rate,
+            ibuf=8000,
+        )
+
+        self._rx = machine.I2S(
+            1,
+            sck=machine.Pin(I2S_PINS["sck_in"], machine.Pin.OUT),
+            ws=machine.Pin(I2S_PINS["ws"], machine.Pin.OUT),
+            sd=machine.Pin(I2S_PINS["sd_in"], machine.Pin.IN),
+            mode=machine.I2S.RX,
+            bits=16,
+            format=machine.I2S.MONO,
+            rate=self.sample_rate,
+            ibuf=8000,
+        )
+
+    def _deinit_i2s(self):
+        if self._tx:
+            self._tx.deinit()
+            self._tx = None
+        if self._rx:
+            self._rx.deinit()
+            self._rx = None
+
+    def run(self):
+        """Run a short duplex session: play a tone while reading mic data."""
+        self._init_i2s()
+        try:
+            tone = self._make_tone_buffer(freq_hz=440, ms=50)
+            read_buf = bytearray(1024)
+            t_end = time.ticks_add(time.ticks_ms(), self.duration_ms)
+
+            while time.ticks_diff(t_end, time.ticks_ms()) > 0:
+                self._tx.write(tone)
+                self._rx.readinto(read_buf)
+        finally:
+            self._deinit_i2s()
+
+    def _make_tone_buffer(self, freq_hz=440, ms=50):
+        samples = int(self.sample_rate * (ms / 1000))
+        buf = bytearray(samples * 2)
+        for i in range(samples):
+            phase = 2 * 3.14159265 * freq_hz * (i / self.sample_rate)
+            sample = int(12000 * __import__("math").sin(phase))
+            buf[i * 2] = sample & 0xFF
+            buf[i * 2 + 1] = (sample >> 8) & 0xFF
+        return buf
+
+
+def run_duplex_test(sample_rate=16000, duration_ms=3000):
+    """Convenience entry point for quick manual tests."""
+    DuplexI2STest(sample_rate=sample_rate, duration_ms=duration_ms).run()
+
+
+if __name__ == "__main__":
+    run_duplex_test()