dev: add interface for opt4048 lux/colour sensor

CMakeLists.txt

@@ -30,6 +30,7 @@ add_executable(ensaht
   src/bmp.c
   src/aht.c
   src/ens.c
+  src/opt4048.c
 )
 
 # Add the standard include files to the build

include/opt4048.h

@@ -0,0 +1,23 @@
+// SPDX-License-Identifier: MIT
+// SPDX-FileCopyrightText: 2026 A.M. Rowsell <amr@frzn.dev>
+
+#ifndef OPT4048_H
+#define OPT4048_H
+
+#include "hardware/i2c.h"
+
+#define OPT_ADDR 0x44
+
+/* Structure to hold the calculated color and lux data */
+typedef struct {
+  float x;
+  float y;
+  float z;
+  float lux;
+} OPT4048_Data;
+
+OPT4048_Data calculate_color_data(float ch0, float ch1, float ch2);
+int initOPT(i2c_inst_t *i2c);
+int getOPTData(i2c_inst_t *i2c, float *ch0, float *ch1, float *ch2);
+
+#endif // OPT4048_H

src/opt4048.c

@@ -0,0 +1,91 @@
+// SPDX-License-Identifier: MIT
+// SPDX-FileCopyrightText: 2026 A.M. Rowsell <amr@frzn.dev>
+
+#include "include/opt4048.h"
+
+OPT4048_Data calculate_color_data(float ch0, float ch1, float ch2) {
+  OPT4048_Data result;
+
+  const float m0x = 2.34892992e-04f;
+  const float m1x = 4.07467441e-05f;
+  const float m2x = 9.28619404e-05f;
+
+  const float m0y = -1.89652390e-05f;
+  const float m1y = 1.98958202e-04f;
+  const float m2y = -1.69739553e-05f;
+
+  const float m0z = 1.20811684e-05f;
+  const float m1z = -1.58848115e-05f;
+  const float m2z = 6.74021520e-04f;
+
+  const float m1l = 2.15e-3f;
+
+  result.x = (ch0 * m0x) + (ch1 * m1x) + (ch2 * m2x);
+  result.y = (ch0 * m0y) + (ch1 * m1y) + (ch2 * m2y);
+  result.z = (ch0 * m0z) + (ch1 * m1z) + (ch2 * m2z);
+
+  result.lux = ch1 * m1l;
+
+  return result;
+}
+
+int initOPT(i2c_inst_t *i2c) {
+  int result = 0;
+  int bytesWritten = 0;
+  // all registers are 16 bits!
+  // Need to init regs as follows:
+  // write setup to CONFIG (0x0A/0x0B)
+  // this sets it to 100ms sample time, auto-range lux
+  static const uint8_t config[5] = {0x0A, 0b00110010, 0b00001000, 0b10000000,
+                                    0b00011101};
+  // we'll be doing single-shot measurements
+  bytesWritten = i2c_write_blocking(i2c, OPT_ADDR, config, 4, false);
+  result = (bytesWritten == 4) ? 0 : 1;
+  return result;
+}
+
+int getOPTData(i2c_inst_t *i2c, float *ch0, float *ch1, float *ch2) {
+  int result = 0;
+  int bytesWritten = 0, bytesRead = 0;
+  uint8_t lightData[16] = {0};
+  uint32_t mantissaCH0 = 0;
+  uint32_t mantissaCH1 = 0;
+  uint32_t mantissaCH2 = 0;
+  uint8_t exponentCH0 = 0;
+  uint8_t exponentCH1 = 0;
+  uint8_t exponentCH2 = 0;
+  static const uint8_t triggerMeas[2] = {0x0B, 0b00101000};
+  static const uint8_t dataReg = 0x00;
+  // force a one-shot measurement
+  bytesWritten = i2c_write_blocking(i2c, OPT_ADDR, triggerMeas, 2, false);
+  if (bytesWritten != 2) {
+    result = 1;
+  }
+  sleep_ms(410); // 4 channels @ 100ms each plus a little buffer time
+
+  bytesWritten = i2c_write_blocking(i2c, OPT_ADDR, &dataReg, 1, true);
+  if (bytesWritten != 1) {
+    result = 1;
+  }
+  bytesRead = i2c_read_blocking(i2c, OPT_ADDR, lightData, 16, false);
+  if (bytesRead != 16) {
+    result = 1;
+  }
+  // now take all the measurement data and convert them to the proper
+  // representation
+  mantissaCH0 = ((uint32_t)(lightData[0] & 0x0FUL) << 16) |
+                ((uint32_t)lightData[1] << 8) | (uint32_t)lightData[2];
+  mantissaCH1 = ((uint32_t)(lightData[4] & 0x0FUL) << 16) |
+                ((uint32_t)lightData[5] << 8) | (uint32_t)lightData[6];
+  mantissaCH2 = ((uint32_t)(lightData[8] & 0x0FUL) << 16) |
+                ((uint32_t)lightData[9] << 8) | (uint32_t)lightData[10];
+  exponentCH0 = (lightData[0] & 0xF0) >> 4;
+  exponentCH1 = (lightData[4] & 0xF0) >> 4;
+  exponentCH2 = (lightData[8] & 0xF0) >> 4;
+
+  *ch0 = (float)(mantissaCH0 << exponentCH0);
+  *ch1 = (float)(mantissaCH1 << exponentCH1);
+  *ch2 = (float)(mantissaCH2 << exponentCH2);
+
+  return result;
+}