turning a pin on and off at a given frequency, and measuring the current while it's on

interrupt_measure.ino

#include <TimerOne.h>

// This example uses the timer interrupt to blink an LED
// and also demonstrates how to share a variable between
// the interrupt and the main program.

float vcc = 5; // volts
float vground = 2.51; // volts -- the virtual ground value
const int led = 3;  // the pin with a LED
float r1 = 3190; // the current-voltage resistance --> amplification 

void setup(void)
{
  pinMode(led, OUTPUT);
  Timer1.initialize(500);
  Timer1.attachInterrupt(blinkLED); // blinkLED to run every 0.15 seconds
  Serial.begin(9600);
}


// The interrupt will blink the LED, and keep
// track of how many times it has blinked.
int ledState = LOW; 
volatile int flag = 0; //whether we're in the 'on' state

void blinkLED(void)
{
  if (ledState == LOW) {
    ledState = HIGH;
    flag = 1; 
    //blinkCount = blinkCount + 1;  // increase when LED turns on
  } else {
    ledState = LOW;
  }
  digitalWrite(led, ledState);
  
}


// The main program will print the blink count
// to the Arduino Serial Monitor
void loop(void)
{

  noInterrupts();
  flag = 0; // write to the flag without conflicting with ISR writes
  interrupts();
  
  while (flag==0) {}; // loop

  // if get here, then flag=1, and we're in the 'on' state
   delayMicroseconds(50); // try to hit the middle of the squarewave (which will be a sinusoid via water), but also give analogRead some time; 
  
   // note that this delay function works well between 3 and 16383 (uS)
   // we might need to come up with a better method later
   // we should put current into water and measure the sinusoidal output to test this out
   // do that, and take photos, tonight
   // then see if you can take an analog reading in the middle of the sinusoid
   // based on where the peak on the scope is at

   // just a test to see if we can independently use pin 9, which might conflict with timer 1 -- not a definitive test
   
   
  // read the input on analog pin 0:
  int sensorValue = analogRead(A0);

  // show that we're done reading
  /*
  digitalWrite(12, HIGH);
  delayMicroseconds(50);
  digitalWrite(12, LOW);
*/

  
  //float r1 = 250000; // kohms -- the resistor used in the first op amp transimpedance amplifier current -> voltage converter
  float v1 = (float(sensorValue)/1024)*vcc; // volts out from the current measurement
  float dv = v1-vground;
  float c1 = float(dv)/float(r1)*1000; // current, in milliamps
  float ca = float(v1)/float(r1)*1000; // current, in milliamps
  // print out the value you read:
  
  Serial.print("bits="); 
  Serial.println(sensorValue);

  Serial.print("volts=");
  Serial.println(v1,5);

  Serial.print("dv (volts) =");
  Serial.println(dv,5);

  Serial.print("current (mA) =");
  Serial.println(c1,5);

  //Serial.print("AC current (mA) =");
  //Serial.println(ca,5);

  Serial.println("\n\n\n\n");
  
  delay(2000);

}