AnalogBurstBackground.ino

Samples A3 continuously in the background with analogStartBurst() and analogBurstDone(), in blocks of 1000 samples at 10000 samples per second. One buffer fills while the other is processed ("double buffering"), and the built-in LED blinks to show that loop() is never blocked. Prints the mean and the RMS of each block, in millivolts.

Output

Serial Monitor at 115200 baud, ten lines a second, for example:

Mean 1023.6 mV, RMS 0.41 mV

// Samples A3 in the background while the sketch keeps working. Each block
// of 1000 samples (0.1 s at 10000 samples/s) is captured into one buffer
// while the previous block, in the other buffer, is processed, so sampling
// restarts within microseconds ("double buffering"). The built-in LED blinks
// to show that loop() is not blocked.
//
// For each block, prints the mean and the RMS of the signal around the mean
// (the AC part), in millivolts.
 
const pin_size_t PIN = A3;
const uint32_t RATE_HZ = 10000;
const size_t BLOCK = 1000;
 
uint16_t buffers[2][BLOCK];
int filling = 0;  // buffer the burst is writing to
unsigned long last_blink = 0;
 
void processBlock(const uint16_t* block) {
    const float mv_per_step = analogFullScaleMillivolts(PIN) / 4096.0f;
    float sum = 0;
    for (size_t i = 0; i < BLOCK; i++) sum += block[i];
    const float mean = sum / BLOCK;
    float squares = 0;
    for (size_t i = 0; i < BLOCK; i++) squares += (block[i] - mean) * (block[i] - mean);
 
    Serial.print("Mean ");
    Serial.print(mean * mv_per_step, 1);
    Serial.print(" mV, RMS ");
    Serial.print(sqrtf(squares / BLOCK) * mv_per_step, 2);
    Serial.println(" mV");
}
 
void setup() {
    Serial.begin(115200);
    while (!Serial) {}
    pinMode(LED_BUILTIN, OUTPUT);
    analogReadResolution(12);
    analogStartBurst(PIN, buffers[filling], BLOCK, RATE_HZ);
}
 
void loop() {
    if (analogBurstDone()) {
        const int full = filling;
        filling = 1 - filling;
        analogStartBurst(PIN, buffers[filling], BLOCK, RATE_HZ);  // next block straight away
        processBlock(buffers[full]);
    }
 
    // Other work carries on while the samples are taken.
    if (millis() - last_blink >= 250) {
        last_blink = millis();
        digitalWrite(LED_BUILTIN, !digitalRead(LED_BUILTIN));
    }
}