Parking Sensor: Distance & Three LEDs

Why it’s here

Use distance thresholds to select three signal states.

How it works

A distance at or below 15 cm selects red. Above 15 and at or below 30 selects amber. Above 30 selects green. Mutually exclusive conditions mean only one output is selected at a time.

Try it

1. Open this experiment
2. Run at 40 cm, then test 30, 16 and 15 cm. Record which light appears at each threshold, including equality.

Connections

• D9 / D10 — Trigger / echo
• D4 / D3 / D2 — Red / amber / green
• GND — Common return

Example sketch

void setup() {
  pinMode(9, OUTPUT);
  pinMode(10, INPUT);
  Serial.begin(9600);
  for (int pin = 2; pin <= 4; pin++) {
    pinMode(pin, OUTPUT);
  }
}

void loop() {
  digitalWrite(9, LOW);
  delayMicroseconds(2);
  digitalWrite(9, HIGH);
  delayMicroseconds(10);
  digitalWrite(9, LOW);
  long cm = pulseIn(10, HIGH) / 58;
  Serial.println(cm);
  digitalWrite(4, cm <= 15);
  digitalWrite(3, cm > 15 && cm <= 30);
  digitalWrite(2, cm > 30);
}

Check your understanding

Which light appears at exactly 15 cm and exactly 30 cm?