diff --git a/exercises/25_motioncal_tbeam/README.md b/exercises/25_motioncal_tbeam/README.md
new file mode 100644
index 0000000..164c700
--- /dev/null
+++ b/exercises/25_motioncal_tbeam/README.md
@@ -0,0 +1,57 @@
+# Exercise 25: MotionCal T-Beam Bridge
+
+Streams the T-Beam Supreme QMC6310 magnetometer in the ASCII format accepted by
+Paul Stoffregen's MotionCal desktop tool.
+
+https://github.com/PaulStoffregen/MotionCal.git (fetch)
+
+MotionCal expects:
+
+```text
+Raw:accel_x,accel_y,accel_z,gyro_x,gyro_y,gyro_z,mag_x,mag_y,mag_z
+```
+
+This exercise only has a magnetometer, so it sends a stationary accelerometer
+placeholder and zero gyro:
+
+```text
+Raw:0,0,8192,0,0,0,mag_x,mag_y,mag_z
+```
+
+The magnetic values are converted from SensorLib Gauss readings into MotionCal's
+integer units where 1 count is 0.1 microtesla.
+
+## Build
+
+```sh
+cd /usr/local/src/microreticulum/microReticulumTbeam/exercises/25_motioncal_tbeam
+source /home/jlpoole/rnsenv/bin/activate
+pio run
+```
+
+## Upload
+
+```sh
+source /home/jlpoole/rnsenv/bin/activate
+pio run -t upload
+```
+
+Use a specific board environment if needed:
+
+```sh
+pio run -e guy -t upload
+```
+
+## MotionCal
+
+Build and run MotionCal as before:
+
+```sh
+cd /usr/local/src/MotionCal
+make WXCONFIG=wx-config LDFLAGS="-lglut -lGLU -lGL -lm"
+GDK_BACKEND=x11 ./MotionCal
+```
+
+Select the T-Beam USB serial port in MotionCal. The firmware also accepts
+MotionCal's 68-byte calibration packet and echoes `Cal1:` and `Cal2:` lines so
+MotionCal can confirm the send.
diff --git a/exercises/25_motioncal_tbeam/platformio.ini b/exercises/25_motioncal_tbeam/platformio.ini
new file mode 100644
index 0000000..f004814
--- /dev/null
+++ b/exercises/25_motioncal_tbeam/platformio.ini
@@ -0,0 +1,77 @@
+; 20260424 Codex
+; Exercise 25_motioncal_tbeam
+
+[platformio]
+default_envs = cy
+
+[env]
+platform = espressif32
+framework = arduino
+board = esp32-s3-devkitc-1
+board_build.partitions = default_8MB.csv
+monitor_speed = 115200
+extra_scripts = pre:scripts/set_build_epoch.py
+lib_deps =
+  Wire
+  olikraus/U8g2@^2.36.4
+  lewisxhe/XPowersLib@0.3.3
+
+build_flags =
+  -I ../../shared/boards
+  -I ../../external/microReticulum_Firmware
+  -I ../../../../LilyGo-LoRa-Series/lib/SensorLib/src
+  -D BOARD_MODEL=BOARD_TBEAM_S_V1
+  -D OLED_SDA=17
+  -D OLED_SCL=18
+  -D OLED_ADDR=0x3C
+  -D ARDUINO_USB_MODE=1
+  -D ARDUINO_USB_CDC_ON_BOOT=1
+
+[env:amy]
+extends = env
+build_flags =
+  ${env.build_flags}
+  -D BOARD_ID=\"AMY\"
+  -D NODE_LABEL=\"Amy\"
+
+[env:bob]
+extends = env
+build_flags =
+  ${env.build_flags}
+  -D BOARD_ID=\"BOB\"
+  -D NODE_LABEL=\"Bob\"
+
+[env:cy]
+extends = env
+build_flags =
+  ${env.build_flags}
+  -D BOARD_ID=\"CY\"
+  -D NODE_LABEL=\"Cy\"
+
+[env:dan]
+extends = env
+build_flags =
+  ${env.build_flags}
+  -D BOARD_ID=\"DAN\"
+  -D NODE_LABEL=\"Dan\"
+
+[env:ed]
+extends = env
+build_flags =
+  ${env.build_flags}
+  -D BOARD_ID=\"ED\"
+  -D NODE_LABEL=\"Ed\"
+
+[env:flo]
+extends = env
+build_flags =
+  ${env.build_flags}
+  -D BOARD_ID=\"FLO\"
+  -D NODE_LABEL=\"Flo\"
+
+[env:guy]
+extends = env
+build_flags =
+  ${env.build_flags}
+  -D BOARD_ID=\"GUY\"
+  -D NODE_LABEL=\"Guy\"
diff --git a/exercises/25_motioncal_tbeam/scripts/set_build_epoch.py b/exercises/25_motioncal_tbeam/scripts/set_build_epoch.py
new file mode 100644
index 0000000..40ef7ca
--- /dev/null
+++ b/exercises/25_motioncal_tbeam/scripts/set_build_epoch.py
@@ -0,0 +1,12 @@
+import time
+Import("env")
+
+epoch = int(time.time())
+utc_tag = time.strftime("%Y%m%d_%H%M%S_z", time.gmtime(epoch))
+
+env.Append(
+    CPPDEFINES=[
+        ("FW_BUILD_EPOCH", str(epoch)),
+        ("FW_BUILD_UTC", '"%s"' % utc_tag),
+    ]
+)
diff --git a/exercises/25_motioncal_tbeam/src/main.cpp b/exercises/25_motioncal_tbeam/src/main.cpp
new file mode 100644
index 0000000..60de5ee
--- /dev/null
+++ b/exercises/25_motioncal_tbeam/src/main.cpp
@@ -0,0 +1,348 @@
+#include <Arduino.h>
+#include <U8g2lib.h>
+#include <Wire.h>
+#include <XPowersLib.h>
+#include <math.h>
+#include <stdint.h>
+#include <string.h>
+
+#include "SensorQMC6310.hpp"
+#include "tbeam_supreme_adapter.h"
+
+namespace {
+
+#ifndef BOARD_ID
+#define BOARD_ID "CY"
+#endif
+
+#ifndef NODE_LABEL
+#define NODE_LABEL "Cy"
+#endif
+
+#ifndef FW_BUILD_UTC
+#define FW_BUILD_UTC unknown
+#endif
+
+#ifndef OLED_SDA
+#define OLED_SDA 17
+#endif
+
+#ifndef OLED_SCL
+#define OLED_SCL 18
+#endif
+
+#ifndef OLED_ADDR
+#define OLED_ADDR 0x3C
+#endif
+
+#define STR_INNER(x) #x
+#define STR(x) STR_INNER(x)
+
+static constexpr const char* kExerciseName = "Exercise 25";
+static constexpr const char* kBoardId = BOARD_ID;
+static constexpr const char* kNodeLabel = NODE_LABEL;
+static constexpr const char* kBuildUtc = STR(FW_BUILD_UTC);
+static constexpr uint32_t kSampleIntervalMs = 40;
+static constexpr uint32_t kDisplayIntervalMs = 250;
+static constexpr uint8_t kMagCandidateCount = 3;
+static constexpr uint8_t kMagCandidates[kMagCandidateCount] = {0x1C, 0x3C, 0x2C};
+static constexpr uint16_t kCalibrationPacketSize = 68;
+static constexpr uint16_t kCalibrationSignature = 0x5475;
+static constexpr size_t kFloatCount = 16;
+
+XPowersLibInterface* g_pmu = nullptr;
+U8G2_SH1106_128X64_NONAME_F_HW_I2C g_oled(U8G2_R0, U8X8_PIN_NONE);
+SensorQMC6310 g_qmc;
+
+bool g_displayReady = false;
+bool g_magReady = false;
+uint8_t g_magAddress = 0;
+uint8_t g_magChipId = 0;
+char g_magLabel[16] = "UNKNOWN";
+uint32_t g_lastSampleMs = 0;
+uint32_t g_lastDisplayMs = 0;
+uint32_t g_sampleCount = 0;
+int16_t g_lastMagCounts[3] = {0, 0, 0};
+float g_lastMagUt[3] = {0.0f, 0.0f, 0.0f};
+
+uint8_t g_calPacket[kCalibrationPacketSize];
+uint16_t g_calPacketLen = 0;
+
+uint16_t crc16Update(uint16_t crc, uint8_t data) {
+  crc ^= data;
+  for (uint8_t i = 0; i < 8; ++i) {
+    if ((crc & 1U) != 0U) {
+      crc = (crc >> 1U) ^ 0xA001U;
+    } else {
+      crc >>= 1U;
+    }
+  }
+  return crc;
+}
+
+float readFloatLe(const uint8_t* p) {
+  union {
+    uint32_t n;
+    float f;
+  } value;
+  value.n = ((uint32_t)p[0]) |
+            ((uint32_t)p[1] << 8U) |
+            ((uint32_t)p[2] << 16U) |
+            ((uint32_t)p[3] << 24U);
+  return value.f;
+}
+
+int16_t clampToInt16(long value) {
+  if (value > INT16_MAX) return INT16_MAX;
+  if (value < INT16_MIN) return INT16_MIN;
+  return (int16_t)value;
+}
+
+int16_t microteslaToMotionCalCounts(float uT) {
+  return clampToInt16(lroundf(uT * 10.0f));
+}
+
+void drawLines(const char* l1,
+               const char* l2 = nullptr,
+               const char* l3 = nullptr,
+               const char* l4 = nullptr,
+               const char* l5 = nullptr) {
+  if (!g_displayReady) {
+    return;
+  }
+
+  g_oled.clearBuffer();
+  g_oled.setFont(u8g2_font_6x12_tf);
+  if (l1) g_oled.drawUTF8(0, 12, l1);
+  if (l2) g_oled.drawUTF8(0, 24, l2);
+  if (l3) g_oled.drawUTF8(0, 36, l3);
+  if (l4) g_oled.drawUTF8(0, 48, l4);
+  if (l5) g_oled.drawUTF8(0, 60, l5);
+  g_oled.sendBuffer();
+}
+
+void initDisplay() {
+  Wire.begin(OLED_SDA, OLED_SCL);
+  Wire.setClock(400000);
+  g_oled.setI2CAddress(OLED_ADDR << 1);
+  g_oled.setBusClock(400000);
+  g_oled.begin();
+  g_oled.setPowerSave(0);
+  g_displayReady = true;
+  drawLines(kExerciseName, "MotionCal Bridge", kBoardId, "starting...");
+}
+
+bool probeI2cAddr(TwoWire& wire, uint8_t addr) {
+  wire.beginTransmission(addr);
+  return wire.endTransmission() == 0;
+}
+
+bool detectMagnetometer() {
+  for (uint8_t i = 0; i < kMagCandidateCount; ++i) {
+    const uint8_t addr = kMagCandidates[i];
+    if (!probeI2cAddr(Wire, addr)) {
+      continue;
+    }
+
+    g_magAddress = addr;
+    if (addr == 0x1C) {
+      strlcpy(g_magLabel, "QMC6310U", sizeof(g_magLabel));
+    } else if (addr == 0x3C) {
+      strlcpy(g_magLabel, "QMC6310N", sizeof(g_magLabel));
+    } else if (addr == 0x2C) {
+      strlcpy(g_magLabel, "QMC5883P", sizeof(g_magLabel));
+    } else {
+      strlcpy(g_magLabel, "QST-MAG", sizeof(g_magLabel));
+    }
+    return true;
+  }
+  return false;
+}
+
+bool initMagnetometer() {
+  if (!detectMagnetometer()) {
+    return false;
+  }
+
+  if (!g_qmc.begin(Wire, g_magAddress, tbeam_supreme::i2cSda(), tbeam_supreme::i2cScl())) {
+    return false;
+  }
+
+  g_magChipId = g_qmc.getChipID();
+  return g_qmc.configMagnetometer(
+      OperationMode::CONTINUOUS_MEASUREMENT,
+      MagFullScaleRange::FS_2G,
+      100.0f,
+      MagOverSampleRatio::OSR_4,
+      MagDownSampleRatio::DSR_1);
+}
+
+void printBootSummary() {
+  Serial.printf("exercise=%s MotionCal T-Beam bridge\r\n", kExerciseName);
+  Serial.printf("board_id=%s node_label=%s build=%s\r\n", kBoardId, kNodeLabel, kBuildUtc);
+  Serial.printf("serial_format=Raw:accel_x,accel_y,accel_z,gyro_x,gyro_y,gyro_z,mag_x,mag_y,mag_z\r\n");
+  Serial.printf("mag_units=MotionCal integer counts, 1 count = 0.1 uT\r\n");
+}
+
+void streamMotionCalRaw(const MagnetometerData& data) {
+  const float xUt = data.magnetic_field.x * 100.0f;
+  const float yUt = data.magnetic_field.y * 100.0f;
+  const float zUt = data.magnetic_field.z * 100.0f;
+
+  g_lastMagUt[0] = xUt;
+  g_lastMagUt[1] = yUt;
+  g_lastMagUt[2] = zUt;
+  g_lastMagCounts[0] = microteslaToMotionCalCounts(xUt);
+  g_lastMagCounts[1] = microteslaToMotionCalCounts(yUt);
+  g_lastMagCounts[2] = microteslaToMotionCalCounts(zUt);
+  ++g_sampleCount;
+
+  Serial.printf("Raw:0,0,8192,0,0,0,%d,%d,%d\r\n",
+                (int)g_lastMagCounts[0],
+                (int)g_lastMagCounts[1],
+                (int)g_lastMagCounts[2]);
+}
+
+void updateDisplay() {
+  char line3[28];
+  char line4[28];
+  char line5[28];
+
+  snprintf(line3, sizeof(line3), "%s 0x%02X id 0x%02X", g_magLabel, g_magAddress, g_magChipId);
+  snprintf(line4, sizeof(line4), "%6.1f %6.1f", g_lastMagUt[0], g_lastMagUt[1]);
+  snprintf(line5, sizeof(line5), "Z:%6.1f N:%lu", g_lastMagUt[2], (unsigned long)g_sampleCount);
+  drawLines(kExerciseName, "MotionCal Raw stream", line3, line4, line5);
+}
+
+void printCalibrationEcho(const float* values) {
+  Serial.printf("Cal1:%.6f,%.6f,%.6f,%.6f,%.6f,%.6f,%.6f,%.6f,%.6f,%.6f\r\n",
+                values[0], values[1], values[2],
+                values[3], values[4], values[5],
+                values[6], values[7], values[8], values[9]);
+  Serial.printf("Cal2:%.6f,%.6f,%.6f,%.6f,%.6f,%.6f,%.6f,%.6f,%.6f\r\n",
+                values[10], values[13], values[14],
+                values[13], values[11], values[15],
+                values[14], values[15], values[12]);
+}
+
+void handleCalibrationPacket(const uint8_t* packet) {
+  const uint16_t signature = (uint16_t)packet[0] | ((uint16_t)packet[1] << 8U);
+  if (signature != kCalibrationSignature) {
+    return;
+  }
+
+  uint16_t crc = 0xFFFF;
+  for (uint16_t i = 0; i < kCalibrationPacketSize - 2; ++i) {
+    crc = crc16Update(crc, packet[i]);
+  }
+  const uint16_t got = (uint16_t)packet[66] | ((uint16_t)packet[67] << 8U);
+  if (crc != got) {
+    Serial.printf("motioncal_calibration_crc=bad expected=0x%04X got=0x%04X\r\n", crc, got);
+    return;
+  }
+
+  float values[kFloatCount];
+  const uint8_t* p = packet + 2;
+  for (size_t i = 0; i < kFloatCount; ++i) {
+    values[i] = readFloatLe(p);
+    p += 4;
+  }
+
+  Serial.printf("motioncal_calibration=received hard_iron_uT=%.3f,%.3f,%.3f field_uT=%.3f\r\n",
+                values[6], values[7], values[8], values[9]);
+  printCalibrationEcho(values);
+}
+
+void pollSerialInput() {
+  while (Serial.available() > 0) {
+    const int c = Serial.read();
+    if (c < 0) {
+      return;
+    }
+
+    if (g_calPacketLen == 0 && (uint8_t)c != 0x75U) {
+      continue;
+    }
+
+    g_calPacket[g_calPacketLen++] = (uint8_t)c;
+    if (g_calPacketLen == 2 && g_calPacket[1] != 0x54U) {
+      g_calPacketLen = (g_calPacket[1] == 0x75U) ? 1U : 0U;
+      if (g_calPacketLen == 1U) {
+        g_calPacket[0] = 0x75U;
+      }
+      continue;
+    }
+
+    if (g_calPacketLen >= kCalibrationPacketSize) {
+      handleCalibrationPacket(g_calPacket);
+      g_calPacketLen = 0;
+    }
+  }
+}
+
+void appSetup() {
+  Serial.begin(115200);
+  const uint32_t serialWaitStart = millis();
+  while (!Serial && (millis() - serialWaitStart) < 4000) {
+    delay(10);
+  }
+  delay(300);
+
+  printBootSummary();
+  initDisplay();
+
+  if (!tbeam_supreme::initPmuForPeripherals(g_pmu, &Serial)) {
+    Serial.println("pmu_init=failed");
+    drawLines(kExerciseName, "PMU init failed", kBoardId, "see serial");
+    return;
+  }
+  Serial.println("pmu_init=ok");
+
+  g_magReady = initMagnetometer();
+  if (!g_magReady) {
+    Serial.println("magnetometer_init=failed");
+    drawLines(kExerciseName, "MAG init failed", kBoardId, "see serial");
+    return;
+  }
+
+  Serial.printf("magnetometer_init=ok label=%s addr=0x%02X chip=0x%02X\r\n",
+                g_magLabel, g_magAddress, g_magChipId);
+  drawLines(kExerciseName, "MotionCal Bridge", g_magLabel, "streaming Raw...");
+  g_lastSampleMs = millis();
+  g_lastDisplayMs = millis();
+}
+
+void appLoop() {
+  pollSerialInput();
+
+  if (!g_magReady) {
+    delay(100);
+    return;
+  }
+
+  const uint32_t now = millis();
+  if ((uint32_t)(now - g_lastSampleMs) >= kSampleIntervalMs) {
+    g_lastSampleMs = now;
+    MagnetometerData data;
+    if (g_qmc.readData(data) && !data.overflow) {
+      streamMotionCalRaw(data);
+    }
+  }
+
+  if ((uint32_t)(now - g_lastDisplayMs) >= kDisplayIntervalMs) {
+    g_lastDisplayMs = now;
+    updateDisplay();
+  }
+
+  delay(1);
+}
+
+}  // namespace
+
+void setup() {
+  appSetup();
+}
+
+void loop() {
+  appLoop();
+}