TabEscaper 3000: The Parent-Proximity Auto-Tab Switcher

1// Arduino Leonardo: HC-SR04 on pins 6 (TRIG) and 7 (ECHO).
2// Send Ctrl+Tab once when distance < 10 cm (will not repeat continuously).
3
4#include <Keyboard.h>
5
6const uint8_t TRIG_PIN = 6;
7const uint8_t ECHO_PIN = 7;
8
9const float THRESHOLD_CM = 30.0;     // trigger threshold
10const unsigned long PULSE_TIMEOUT = 30000UL; // microseconds (30 ms) timeout
11
12bool sentOnce = false; // ensures single send while object stays < threshold
13
14void setup() {
15  pinMode(TRIG_PIN, OUTPUT);
16  pinMode(ECHO_PIN, INPUT);
17  digitalWrite(TRIG_PIN, LOW);
18  Serial.begin(9600);
19  // Allow the USB stack to settle before sending HID events
20  delay(1000);
21  Keyboard.begin();
22}
23
24void loop() {
25  float distance = readDistanceCM();
26
27  Serial.print("Distance (cm): ");
28  if (distance >= 0) {
29    Serial.println(distance, 2);
30  } else {
31    Serial.println("timeout");
32  }
33
34  if (distance >= 0 && distance < THRESHOLD_CM) {
35    if (!sentOnce) {
36      sendCtrlTab();
37      sentOnce = true;
38      Serial.println("Sent Ctrl+Tab");
39    }
40  } else {
41    // reset flag when object moves away (allows next Ctrl+Tab when it comes close again)
42    sentOnce = false;
43  }
44
45  delay(100); // modest sampling interval (10 Hz)
46}
47
48float readDistanceCM() {
49  // Trigger the sensor: a 10µs HIGH on TRIG
50  digitalWrite(TRIG_PIN, LOW);
51  delayMicroseconds(2);
52  digitalWrite(TRIG_PIN, HIGH);
53  delayMicroseconds(10);
54  digitalWrite(TRIG_PIN, LOW);
55
56  // Read echo pulse (microseconds) with timeout
57  unsigned long duration = pulseIn(ECHO_PIN, HIGH, PULSE_TIMEOUT);
58
59  if (duration == 0) {
60    // timeout (no echo) -> return -1 to indicate invalid
61    return -1.0;
62  }
63
64  // Distance in cm: sound speed ~ 343 m/s -> 29.1 µs per cm round-trip
65  // distance = (duration / 2) / 29.1
66  float distanceCm = (duration / 2.0) / 29.1;
67  return distanceCm;
68}
69
70void sendCtrlTab() {
71  // Press modifier (left ctrl) + tab, hold briefly, then release
72  Keyboard.press(KEY_LEFT_CTRL);
73  Keyboard.press(KEY_TAB);
74  delay(100); // hold for 100 ms
75  Keyboard.releaseAll();
76}