Hello Everyone , I am new to programming in IDE. I am using built-in timer of arduino.I am using TDR method to capture reflection from fault location in cable and for that I am using timer.Timer should start as soon as output is send and stop at reflection. I have a reference code for it but I dont able to understand it, so if anyone know about it , it would be great.
// Time domain reflectometer
const int stepPin = 4; // digital output pin we generate the step on. Later in the code, we assume this is port D bit 4.
const int refPin = 11; // PWM output pin that we use to generate the comparator reference voltage. Must be on timer 2.
const int shutdownPin = 7; // digital output port used to put comparator in shutdown mode - drive HIGH before sleeping
const int maxSteps = 4; // maximum number of steps in each direction that we capture
// Define the fraction of the speed of light at which waves propagate in the cable
// Some typical values;
// cat 5 cable 68%
// RG58 or RG213 coax (solid polyethylene dieletric) 66%
// Airspaced coax up to 92%
const float propagationFactor = 0.68; // fraction of speed of light that waves travel in the cable under test
void setup()
{
pinMode(stepPin, OUTPUT);
pinMode(refPin, OUTPUT);
pinMode(shutdownPin, OUTPUT);
TCCR1A = 0;
TCCR1B = (1 << ICNC1); // input capture noise canceller enabled, capture on falling edge
TIMSK1 = 0; // timer 1 interrupts disabled
ACSR = 0; // input capture from ICP1 pin
TCCR2B = (1 << CS20); // change timer 2 PWM frequency to 31.25kHz because we're using pin 11 as a DAC
Serial.begin(19200);
}
struct Step
{
unsigned int time;
unsigned int amplitude;
};
// Take a single measurement, using either a positive or negative edge from the comparator.
// The comparator reference voltage must have been set up and allowed to stablise before calling this.
unsigned int takeMeasurement(bool posEdge)
{
byte reg1b = (posEdge) ? 0 : (1 << ICES1); // input capture noise canceller csdisabled, set up input capture polarity, stop timer
reg1b |= (1 << CS10);
TCCR1B = reg1b;
TCNT1H = 0;
TCNT1L = 0; // clear timer
unsigned int capture = 0;
unsigned long start = micros(); // get the time
cli();
TCNT1H = 0;
TCNT1L = 0; // clear timer
TIFR1 = (1 << ICF1); // clear timer 1 input capture bit
PORTD |= (1 << 4); // set output high
sei();
do
{
if ((TIFR1 & (1 << ICF1)) && capture == 0)
{
byte temp = ICR1L;
capture = (ICR1H << 8) | temp;
}
} while (micros() - start < 100);
PORTD &= ~(1 << 4); // set output low
return capture;
}
size_t findSteps(bool positive, struct Step *results, size_t maxResults)
{
byte amplitude = (positive) ? 5 : 250;
analogWrite(refPin, amplitude);
delay(100); // wait 100ms for the output to stabilise
unsigned int lastReading = 0;
size_t numResults = 0;
unsigned int stepSize = 0; // 0 means not in a step
#ifdef DEBUG
Serial.print((positive) ? "pos " : "neg ");
#endif
for (int i = 0; i < 50; ++i)
{
analogWrite(refPin, amplitude);
delay(10);
unsigned int currentReading = takeMeasurement(positive);
unsigned int currentDiff = currentReading - lastReading; // diff since start of possible step
if (stepSize == 0)
{
// Not currently in a step
if (i != 0 && currentReading != 0 && currentDiff == 0)
{
// Found the start of a possible step
++stepSize;
}
lastReading = currentReading;
}
else
{
if (currentDiff > 2 || i + 1 == 50)
{
// Step has endeed, so record it if it is big enough
if (stepSize >= 2)
{
results->time = lastReading;
results->amplitude = amplitude - 5;
++results;
++numResults;
if (numResults == maxResults) break;
}
stepSize = 0;
lastReading = currentReading;
}
else if (currentDiff == 0)
{
++stepSize;
}
}
#ifdef DEBUG
if (i != 0) Serial.write(',');
Serial.print(currentReading);
#endif
if (positive)
{
amplitude += 5;
}
else
{
amplitude -= 5;
}
}
#ifdef DEBUG
Serial.println();
#endif
return numResults;
}
// Convert a number of clocks delay to a cable length in metres
float clocksToMetres(unsigned int clocks)
{
float delayTime = (float)clocks/(float)F_CPU; // delay in seconds
float distance in metres= (delayTime * 3.0e8 * propagationFactor)/2.0;
Serial.print("distance in metres: ");
return (distance in metres);
}
// Diagnose the cable condition. We have the following common possibilities:
// 1. No cable connected, or a very short open-circuit cable connected.
// In this case we should see the original positive step, very close to zero delay, with amplitude nearly 5V.
// 2. Direct short, or very short cable with shorted end.
// In this case, we will not even see the original positive-going step, or it will have a very low amplitude.
// 3. Cable with open circuit.
// We see the original positive step close to zero delay, and a further positive step going to nearly twice the amplitude later.
// 4. Cable with short circuit.
// We see the original positive step close to zero delay, and a negative step going back down to nearly zero later.
// 5. Correctly terminated cable.
// We see only the original positive step, with amplitudfe well below 5V.
void loop()
{
Step posSteps[maxSteps], negSteps[maxSteps];
size_t numPosSteps = findSteps(true, posSteps, maxSteps);
size_t numNegSteps = findSteps(false, negSteps, maxSteps);
if (numPosSteps == 0)
{
Serial.print("Direct short");
}
else if (numPosSteps == 1 && numNegSteps == 0)
{
if (posSteps[0].amplitude >= 200)
{
Serial.print("No cable connected");
}
else
{
Serial.print("Cable correctly terminated");
}
}
else if (numPosSteps >= 2 && numNegSteps == 0)
{
Serial.print("Open at ");
Serial.print(clocksToMetres(posSteps[1].time - posSteps[0].time), 1);
}
else if (numPosSteps == 1 && numNegSteps == 1)
{
Serial.print("Short at ");
Serial.print(clocksToMetres(negSteps[0].time - posSteps[0].time), 1);
}
else
{
Serial.print("Failed to diagnose fault");
}
#ifdef DEBUG
Serial.print(" (pos=");
for (size_t i = 0; i < numPosSteps; ++i)
{
if (i != 0)
{
Serial.write(',');
}
Serial.print(posSteps[i].time);
Serial.write('|');
Serial.print(posSteps[i].amplitude);
}
Serial.print(" neg=");
for (size_t i = 0; i < numNegSteps; ++i)
{
if (i != 0)
{
Serial.write(',');
}
Serial.print(negSteps[i].time);
Serial.write('|');
Serial.print(negSteps[i].amplitude);
}
Serial.println(")");
#else
Serial.println();
#endif
}
