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Fix multiple timing errors in example sketch #6

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Fix multiple timing errors in example sketch #6

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21 changes: 14 additions & 7 deletions examples/SimpleEMGFilters/SimpleEMGFilters.ino
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Original file line number Diff line number Diff line change
Expand Up @@ -75,7 +75,10 @@ EMGFilters myFilter;
SAMPLE_FREQUENCY sampleRate = SAMPLE_FREQ_1000HZ;

// Time interval for processing the input signal.
unsigned long long interval = 1000000ul / sampleRate;
unsigned long interval = 1000000ul / sampleRate;

// Value of micros() right before taking a sample.
unsigned long timeStamp;

// Set the frequency of power line hum to filter out.
//
Expand All @@ -89,12 +92,12 @@ void setup() {

// open serial
Serial.begin(115200);

// Initial timestamp.
timeStamp = micros();
}

void loop() {
// Note: `micros()` will overflow and reset every about 70 minutes.
unsigned long long timeStamp = micros();

int data = analogRead(SensorInputPin);

// filter processing
Expand All @@ -104,7 +107,6 @@ void loop() {
int envelope = sq(dataAfterFilter);

if (CALIBRATE) {
Serial.print("Squared Data: ");
Serial.println(envelope);
}
else {
Expand All @@ -119,11 +121,16 @@ void loop() {

// Usually, you should still have (interval - timeElapsed) to do other work.
// Otherwise, you would have to lower down the `sampleRate`.
unsigned long long timeElapsed = micros() - timeStamp;
unsigned long timeElapsed = micros() - timeStamp;
#if _DEBUG
Serial.print("Filters cost time: ");
Serial.println(timeElapsed);
Serial.flush();
timeStamp = micros();
#else
delay((interval - timeElapsed) / 1000);
if (interval > timeElapsed) {
delayMicroseconds(interval - timeElapsed);
}
timeStamp += interval;
#endif
}