OpenGage Mode in Practice: Wireless Environmental Monitoring with the SHT45 and Arduino Nano ESP32

				
					// ============================================================
// OpenGage Mode — Environmental Monitor Example
// MicroRidge MobileCollect Mini Mobile Module EVO (M3E)
// Hardware: Arduino Nano ESP32 + Adafruit SHT45
//
// On each trigger event (auto every 40 seconds, or operator
// pressing the Read Button on the M3E), transmits a single
// combined packet:
//   Temp F[TAB]72.7[TAB]RH %[TAB]48.3
//
// Each label and value lands in its own Excel column so values
// can be charted or referenced directly without text parsing:
//   Col A: Temp F  |  Col B: 72.7  |  Col C: RH %  |  Col D: 48.3
//
// Trigger modes:
//   Auto   — Arduino triggers a read every 40 seconds.
//             800,000 M3E readings at this interval ≈ 1 year
//             of battery life on a single CR2032 coin cell.
//   Manual — Operator presses the Read Button on the M3E.
//             Resets the auto-trigger timer — no double-fire.
//
// Wiring (Arduino Nano ESP32):
//   Pin D2  (OUTPUT) → Green wire  → Read Button on M3E
//   Pin D3  (INPUT)  → White wire  → Read Request from M3E
//   Pin D6  (TX)     → Black wire  → UART Data to M3E
//   Pin A4  (SDA)    → SDA         → SHT45 SDA
//   Pin A5  (SCL)    → SCL         → SHT45 SCL
//   3.3V             → VIN         → SHT45 VIN
//   GND              → Blue wire + SHT45 GND → Common Ground
//
// Required Libraries (Arduino Library Manager):
//   Adafruit SHT4x Library
//   Adafruit BusIO
//
// Before running: configure M3E in OpenGage Mode (9600-N-8-1)
// using MobileCollect Xpress Setup or Extended Setup, and pair
// with an EVO series MobileCollect Base Receiver.
// ============================================================

#include <Wire.h>
#include "Adafruit_SHT4x.h"

// ── Pin Definitions ──────────────────────────────────────────
#define READ_BUTTON_PIN   2     // OUTPUT: Pull LOW 25–50 ms to auto-trigger.
#define READ_REQUEST_PIN  3     // INPUT:  M3E pulls LOW when ready to receive.
#define UART_TX_PIN       6     // Serial1 TX → Black wire → M3E UART input.

// ── End-of-Packet Byte ───────────────────────────────────────
#define END_OF_PACKET     0x0D  // Carriage Return — required packet terminator.

// ── Timing ───────────────────────────────────────────────────
// 40-second interval: 800,000 M3E readings ≈ 1 year per CR2032.
// Adjust READ_INTERVAL_MS to trade battery life for sample rate.
const unsigned long READ_INTERVAL_MS        = 40000;
const unsigned long READ_BUTTON_PULSE_MS    = 25;
const unsigned long READ_REQUEST_TIMEOUT_MS = 500;
const unsigned long SENSOR_POLL_MS          = 5000;

// ── State ────────────────────────────────────────────────────
unsigned long lastReadTime   = 0;
unsigned long lastSensorPoll = 0;
bool sensorReady             = false;

// ── Cached Sensor Values ─────────────────────────────────────
// SHT45 is polled every 5 seconds in the background.
// Transmit reads from cache — no blocking sensor reads during
// the time-sensitive Read Request response window.
float cachedTempF    = 0.0;
float cachedHumidity = 0.0;

// ── SHT45 ────────────────────────────────────────────────────
Adafruit_SHT4x sht45;

// ── Setup ────────────────────────────────────────────────────
void setup() {
  Serial1.begin(9600, SERIAL_8N1, -1, UART_TX_PIN);

  Wire.begin();
  if (!sht45.begin(&Wire)) {
    while (1) delay(10);  // Halt — sensor required.
  }
  sht45.setPrecision(SHT4X_HIGH_PRECISION);

  pinMode(READ_BUTTON_PIN, OUTPUT);
  digitalWrite(READ_BUTTON_PIN, HIGH);
  pinMode(READ_REQUEST_PIN, INPUT_PULLUP);
}

// ── pollSensor() ─────────────────────────────────────────────
// Reads SHT45 and caches values. Called on SENSOR_POLL_MS
// interval. Non-blocking — does not affect M3E timing.
// ─────────────────────────────────────────────────────────────
void pollSensor() {
  sensors_event_t humidityEvent, tempEvent;
  if (sht45.getEvent(&humidityEvent, &tempEvent)) {
    cachedTempF    = (tempEvent.temperature * 9.0 / 5.0) + 32.0;
    cachedHumidity = humidityEvent.relative_humidity;
    sensorReady    = true;
  }
}

// ── transmit() ───────────────────────────────────────────────
// Sends combined temp + humidity packet to M3E via UART.
// Labels and values are tab-separated into individual columns
// so values can be graphed or referenced directly in Excel
// without any text parsing.
// Format: "Temp F[TAB]72.7[TAB]RH %[TAB]48.3" + 0x0D
//
// Excel column layout:
//   Col A: Temp F  |  Col B: 72.7  |  Col C: RH %  |  Col D: 48.3
// ─────────────────────────────────────────────────────────────
void transmit() {
  if (!sensorReady) return;

  String packet = "Temp F\t" + String(cachedTempF, 1) + "\t" +
                  "RH %\t"   + String(cachedHumidity, 1);

  Serial1.print(packet);
  Serial1.write(END_OF_PACKET);
  delay(150);  // 150 ms minimum gap between M3E packets.
}

// ── Main Loop ────────────────────────────────────────────────
void loop() {
  unsigned long now = millis();

  // Background sensor poll — keeps cached values current.
  if (now - lastSensorPoll >= SENSOR_POLL_MS) {
    pollSensor();
    lastSensorPoll = now;
  }

  // Path 1: Auto-trigger every 40 seconds.
  if (now - lastReadTime >= READ_INTERVAL_MS) {
    digitalWrite(READ_BUTTON_PIN, LOW);
    delay(READ_BUTTON_PULSE_MS);
    digitalWrite(READ_BUTTON_PIN, HIGH);

    unsigned long waitStart = millis();
    while (millis() - waitStart < READ_REQUEST_TIMEOUT_MS) {
      if (digitalRead(READ_REQUEST_PIN) == LOW) {
        transmit();
        lastReadTime = millis();
        break;
      }
    }
    if (millis() - lastReadTime > READ_REQUEST_TIMEOUT_MS) {
      lastReadTime = millis();
    }
  }

  // Path 2: Manual trigger — operator presses Read Button on M3E.
  // Resets auto-trigger timer to prevent duplicate transmission.
  else if (digitalRead(READ_REQUEST_PIN) == LOW) {
    transmit();
    lastReadTime = millis();
  }
}