Long-Life Barometer Logger

#include <Wire.h>

const int DONE_PIN = 4, DUMP_PIN = 5;
const uint8_t LPS = 0x5D, FRAM = 0x50;
const uint16_t REC_SIZE = 4, DATA_START = 4, MAX_RECS = (32768 - DATA_START) / REC_SIZE;

void reg8(uint8_t addr, uint8_t reg, uint8_t val) {
  Wire.beginTransmission(addr); Wire.write(reg); Wire.write(val); Wire.endTransmission();
}
void readBytes(uint8_t addr, uint8_t reg, uint8_t* d, int n) {
  Wire.beginTransmission(addr); Wire.write(reg); Wire.endTransmission(false);
  Wire.requestFrom(addr, (uint8_t)n);
  for (int i = 0; i < n; i++) d[i] = Wire.read();
}
void framWrite(uint16_t a, const uint8_t* d, int n) {
  Wire.beginTransmission(FRAM); Wire.write(a >> 8); Wire.write(a & 0xFF); Wire.write(d, n); Wire.endTransmission();
}
void framRead(uint16_t a, uint8_t* d, int n) {
  Wire.beginTransmission(FRAM); Wire.write(a >> 8); Wire.write(a & 0xFF); Wire.endTransmission(false);
  Wire.requestFrom(FRAM, (uint8_t)n);
  for (int i = 0; i < n; i++) d[i] = Wire.read();
}
uint32_t getCount() { uint32_t c; framRead(0, (uint8_t*)&c, 4); return c > MAX_RECS ? 0 : c; }
void setCount(uint32_t c) { framWrite(0, (uint8_t*)&c, 4); }

bool measure(float& hPa, float& tC) {
  reg8(LPS, 0x10, 0x02);                 // CTRL_REG1: one-shot mode, block data update
  reg8(LPS, 0x11, 0x11);                 // CTRL_REG2: auto-increment + start one-shot
  for (int i = 0; i < 50; i++) {         // wait for pressure ready (max ~50 ms)
    uint8_t st; readBytes(LPS, 0x27, &st, 1);
    if (st & 0x01) {
      uint8_t d[5]; readBytes(LPS, 0x28, d, 5);
      int32_t p = (int32_t)d[0] | ((int32_t)d[1] << 8) | ((int32_t)d[2] << 16);
      hPa = p / 4096.0;
      tC = (int16_t)(d[3] | (d[4] << 8)) / 100.0;
      return true;
    }
    delay(1);
  }
  return false;
}

void setup() {
  pinMode(DONE_PIN, OUTPUT);
  digitalWrite(DONE_PIN, LOW);
  pinMode(DUMP_PIN, INPUT_PULLUP);
  Wire.begin(6, 7);

  if (digitalRead(DUMP_PIN) == LOW) {    // dump mode: stay awake for commands
    Serial.begin(115200);
    delay(1500);
    Serial.println("Dump mode. d = print CSV, x = erase");
    return;
  }

  float hPa, tC;
  uint32_t n = getCount();
  if (n < MAX_RECS && measure(hPa, tC)) {
    uint16_t rec[2] = { (uint16_t)(hPa * 10), (uint16_t)(int16_t)(tC * 100) };
    framWrite(DATA_START + n * REC_SIZE, (uint8_t*)rec, REC_SIZE);
    setCount(n + 1);
  }
  digitalWrite(DONE_PIN, HIGH);          // TPL5110 cuts the power here
  delay(100);
}

void loop() {
  if (digitalRead(DUMP_PIN) != LOW || !Serial.available()) return;
  char c = Serial.read();
  if (c == 'x') { setCount(0); Serial.println("Erased"); }
  if (c == 'd') {
    uint32_t n = getCount();
    Serial.println("sample,pressure_hpa,temperature_c");
    for (uint32_t i = 0; i < n; i++) {
      uint16_t rec[2];
      framRead(DATA_START + i * REC_SIZE, (uint8_t*)rec, REC_SIZE);
      Serial.printf("%lu,%.1f,%.2f\n", (unsigned long)i, rec[0] / 10.0, (int16_t)rec[1] / 100.0);
    }
  }
}