Allow setting list of pins to sample after construction

examples/Advanced/ADC_Multi_Channel_Dynamic/ADC_Multi_Channel_Dynamic.ino

@@ -0,0 +1,74 @@
+/* ADC Multi Channel sampling usage demo
+ *
+ * Queries for pin numbers to sample on the Serial Monitor, then records and prints three readings on
+ * each of those pins at a leisurely rate of 2 Hz.
+ */
+
+#include <Arduino_AdvancedAnalog.h>
+
+AdvancedADC adc;
+uint64_t last_millis = 0;
+pin_size_t active_pins[AN_MAX_ADC_CHANNELS];
+int num_active_pins = 0;
+const int samples_per_round = 3;
+
+void queryPins() {
+    Serial.println("Enter pins to sample (number only, e.g. 3,4 for A3, and A4). Enter to repeat previous round.");
+
+    int old_num_active_pins = num_active_pins;
+    num_active_pins = 0;
+    String buf;
+    int c;
+    do {
+        c = Serial.read();
+        if (c < 0) continue;
+
+        if (c == ',' || c == '\n') {
+            buf.trim();
+            if (buf.length()) {
+                active_pins[num_active_pins++] = buf.toInt() + A0;
+                buf = String();
+            }
+        } else {
+            buf += (char) c;
+        }
+    } while (!(c == '\n' || num_active_pins >= AN_MAX_ADC_CHANNELS));
+
+    // No (valid) input? Repeat previous measurement cylce
+    if (!num_active_pins) {
+        num_active_pins = old_num_active_pins;
+    }
+}
+
+void setup() {
+    Serial.begin(9600);
+    while (!Serial) {};
+}
+
+void loop() {
+    queryPins();
+    if (num_active_pins) {
+        // Resolution, sample rate, number of samples per buffer per channel, queue depth, number of pins, array of pins.
+        if (!adc.begin(AN_RESOLUTION_16, 2, 1, samples_per_round, num_active_pins, active_pins)) {
+            Serial.println("Failed to start analog acquisition!");
+            while (1);
+        }
+
+        for (int i = 0; i < samples_per_round; ++i) {
+            while(!adc.available()) {};  // Your code could do something useful while waiting!
+
+            SampleBuffer buf = adc.read();
+
+            for (int i = 0; i < num_active_pins; ++i) {
+                Serial.print(buf[i]);
+                Serial.print(" ");
+            }
+            Serial.println();
+
+            // Release the buffer to return it to the pool.
+            buf.release();
+        }
+
+        adc.stop();
+    }
+}

src/AdvancedADC.h

@@ -42,10 +42,19 @@ class AdvancedADC {
                 adc_pins[n_channels++] = analogPinToPinName(p);
             }
         }
+        AdvancedADC(): n_channels(0), descr(nullptr) {}
         ~AdvancedADC();
         bool available();
         SampleBuffer read();
         int begin(uint32_t resolution, uint32_t sample_rate, size_t n_samples, size_t n_buffers);
+        int begin(uint32_t resolution, uint32_t sample_rate, size_t n_samples, size_t n_buffers, size_t n_pins, pin_size_t *pins) {
+            if (n_pins > AN_MAX_ADC_CHANNELS) n_pins = AN_MAX_ADC_CHANNELS;
+            for (size_t i = 0; i < n_pins; ++i) {
+                adc_pins[i] = analogPinToPinName(pins[i]);
+            }
+            n_channels = n_pins;
+            return begin(resolution, sample_rate, n_samples, n_buffers);
+        }
         int stop();
 };