Add NPN buzzer projects

activebuzzer_npn_lowside_switching/activebuzzer_npn_lowside_switching.ino

@@ -0,0 +1,31 @@
+#define PIN_BUZZER_SWITCH 14
+#define PIN_BUTTON        21
+#define PWM_CHANNEL       0
+
+void setup() {
+  pinMode(PIN_BUZZER_SWITCH, OUTPUT);
+  pinMode(PIN_BUTTON, INPUT);
+  // Tutorial had a bug here. Needs to be freq=1000, not freq=1.
+  ledcAttachChannel(PIN_BUZZER_SWITCH, 1000, 10, PWM_CHANNEL);
+  ledcWriteTone(PIN_BUZZER_SWITCH, 2000);
+  delay(300);
+}
+
+void alarm() {
+  float sine;
+  int tone;
+  for ( int i = 0; i < 360 ; i += 10 ) { 
+    sine = sin(i * (PI / 180));
+    tone = 2000 + sine * 500;
+    ledcWriteTone(PIN_BUZZER_SWITCH, tone);
+    delay(50);
+  }
+}
+
+void loop() {
+  if ( digitalRead(PIN_BUTTON) == LOW ) {
+    alarm();
+  } else { 
+    ledcWriteTone(PIN_BUZZER_SWITCH, 0);
+  }
+}

buzzer-npn-lowside-switching/buzzer-npn-lowside-switching/buzzer-npn-lowside-switching.ino

@@ -0,0 +1,15 @@
+#define PIN_BUZZER_SWITCH 14
+#define PIN_BUTTON        21
+
+void setup() {
+  pinMode(PIN_BUZZER_SWITCH, OUTPUT);
+  pinMode(PIN_BUTTON, INPUT);
+}
+
+void loop() {
+  if ( digitalRead(PIN_BUTTON) == LOW ) {
+    digitalWrite(PIN_BUZZER_SWITCH, HIGH);
+  } else { 
+    digitalWrite(PIN_BUZZER_SWITCH, LOW);
+  }
+}

flowing_light_with_button/README.md

@@ -31,7 +31,7 @@ if (digitalRead(PIN_BUTTON) == LOW) {
    // do something with the pin
 ```
 
-... This is really wasteful. I paid good money for those CPU cycles, and on embedded hardware we don't have a lot of them to go around. (The ESP32-S3 has an Xtensa dual-core 32-bit LX7 running up to 240Mhz - stunning when you think about the price and size of the package, but still, not enough to be wasteful.) I improved that by using a timer in a function that yields time back to the CPU while it's waiting to verify that the button is debounced.
+... This is not great. First, we are wasting CPU cycles (The ESP32-S3 has an Xtensa dual-core 32-bit LX7 running up to 240Mhz - stunning when you think about the price and size of the package, but still, not enough to be wasteful). But on the ESP32-S3 in particular, the solution package as a whole isn't losing those cycles - it runs Arduino on top of an RTOS, so `delay()` is actually yielding back to the RTOS scheduler so that things like bluetooth and wifi stacks can continue. But *our* program is fully blocked here. If I want to scan additional buttons, or perform some other task, we're locked in here. So I improved that by using a timer in a function that yields time back to the CPU while it's waiting to verify that the button is debounced.
 
 ```arduino
 void checkButtonPressed(void) {