Arduino / ESP8266使用中断采样

1 回答

• 0

  所以，让我自己回答 .

  对于时间分辨率：通过使用计算处理器周期的 ESP.getCycleCount() 可以获得更精确的时间 - 在我的80 MHz NodeMCU板上，每个周期为12.5 ns或每微秒80个周期 . 我应该在第一部分中提到过 .

  中断：这是我误解的 . 现在我通过让main函数在循环中等待直到达到超时（设置为1毫秒，正常预期时间在1-100微秒范围内）或者直到中断函数设置了全局变量来解决它 . 所以现在我测量的是12.5纳秒的分辨率！

  这个草图中缺少的一件事是修正处理时序所需的程序时间：从EC引脚上的值下降到开始计数所需的时间，以及从接收中断到停止计数所需的时间 . 如果这个开销是100个周期，那将是1.25微秒，这完全在我的测量时间内 .

  //基于电容的TDS测量

  // pin D5 C+ - 330 ohm resistor----------|------------|       
  //                                       |            |
  //                                        cap        EC probe or
  //                                       |           resistor (for simulation)
  // pin D6 C- ----------------------------|            |
  //                                                    |
  // pin A0 EC -----------------------------------------|
  
  #include <Average.h>
  
  int capPos = D5;  //C+
  int capNeg = D6;  //C-
  int EC = D7;      //EC
  unsigned long startCycle;
  unsigned long endCycle;
  #define CYCLETIME 12.5 // the time it takes in nanoseconds to complete one CPU cycle (12.5 ns on a 80 MHz processor)
  
  float CAP = 47; // capacity in nF
  #define calibration 150 // a calibration factor to link time with EC.
  
  void setup() {
    Serial.begin(9600);
  }
  
  void loop () {
    float EC = getEC(); // get the EC as mS/cm.
    Serial.println (", EC: " + String(EC) + " mS/cm");
    delay(500);
  }
  
  float getEC() {
  
    int samples = 100;              // number of EC samples to take and average.
    unsigned long startTime;        // the time stamp (in microseconds) the measurement starts.
    unsigned long endTime;          // the time stamp (in microseconds) the measurement is finished.
    unsigned int dischargeTime;    // the time it took for the capacitor to discharge.
    Average<unsigned int> discharge(samples); // The sampling results.
    unsigned int chargeDelay = 500;         // The time (in microseconds) given to the cap to fully charge/discharge - about 10x RC is a good value.
    unsigned int timeout = 1;  // discharge timeout in milliseconds - if not triggered within this time, the EC probe is probably not there.
  
    int startLevel; // analog level of the pin.
    int endLevel;
    pinMode(A0, INPUT);
  
    for(int i=0; i<samples; i++) { // take <samples> measurements of the EC.
  
      // Stage 1: fully charge capacitor for positive cycle.
      // C+ high, C- low, EC disconnected.
      pinMode (EC, INPUT);
      pinMode (capPos,OUTPUT);
      digitalWrite (capPos, HIGH);
      pinMode (capNeg, OUTPUT);
      digitalWrite (capNeg, LOW);
      delayMicroseconds(chargeDelay);
  
      // Stage 2: positive side discharge; measure time it takes.
      // C+ disconnected, C- low, EC low.
      startCycle = ESP.getCycleCount();
      pinMode (capPos,INPUT); //set C+ to input to keep voltage from grounding a discharging thru this output pin
      pinMode (EC, OUTPUT); 
      digitalWrite (EC, LOW);
  
      // Use cycle counts and an interrupt to get a much more precise time measurement, especially for high-EC situations.
      endCycle = 0;
      startTime = millis();
      attachInterrupt(digitalPinToInterrupt(capPos), capDischarged, FALLING);
      while (endCycle == 0) {
        if (millis() > (startTime + timeout)) break;
      }
      detachInterrupt(digitalPinToInterrupt(capPos));
      if (endCycle == 0) dischargeTime = 0;
      else {
  
        // Handle potential overflow of micros() just as we measure, this happens about every 54 seconds
        // on a 80-MHz board.
        if (endCycle < startCycle) dischargeTime = (4294967295 - startCycle + endCycle) * CYCLETIME;
        else dischargeTime = (endCycle - startCycle) * CYCLETIME;
        discharge.push(dischargeTime);
      }
  
      // Stage 3: fully charge capacitor for negative cycle. C+ low, C- high, EC disconnected.
      pinMode (EC, INPUT); 
      pinMode (capPos,OUTPUT);
      digitalWrite (capPos, LOW);
      pinMode (capNeg, OUTPUT);
      digitalWrite (capNeg, HIGH);
      delayMicroseconds(chargeDelay);
  
      // Stage 4: negative side charge; don't measure as we just want to balance it the directions.
      // C+ disconnected, C- high, EC high.
      pinMode (capPos,INPUT); //set C+ to input to keep voltage from grounding a discharging thru this output pin
      pinMode (EC, OUTPUT); 
      digitalWrite (EC, HIGH);
      delayMicroseconds(dischargeTime/1000);
  
    }
    float dischargeAverage = discharge.mean();
    Serial.print("Discharge time: ");
    Serial.print(dischargeAverage);
  
    // Calculate EC from the discharge time.
  
    return dischargeAverage;
  }
  
  // Upon interrupt: register the cycle count of when the cap has discharged.
  void capDischarged() {
    endCycle = ESP.getCycleCount();
    detachInterrupt(digitalPinToInterrupt(capPos));
  }
  

  回复于 2024-05-02T01:24:44+08:00