Ultrasonic Distance Meter

The finish line

What you will build

The meter reports targets from 10 to 100 cm with average error under 3 cm across five marked positions.

Before you build

Materials, tools, and safety

Reuse-material cost: Usually under $5 with an existing kit. Supervision: Adult guidance recommended for wiring and cutting.

Build it

Step-by-step instructions

1. Step 1

   Mount the sensor

   Fix the two transducers level on a card stand.

   Keep the front openings clear.

2. Step 2

   Wire rated power

   Connect VCC and ground, then join trigger and echo to chosen pins.

   Add level shifting if the board requires it.

3. Step 3

   Send a clean trigger

   Drive trigger low, high for 10 microseconds, then low.

   Wait between measurements.

   Builder checkpoint: After send a clean trigger, the first subassembly should stay aligned when handled gently.

4. Step 4

   Read echo duration

   Use a timeout so missing echoes cannot freeze the program.

   Print raw microseconds.

   Watch for: If this stage binds or drifts, inspect timing resolution before adding more parts.

5. Step 5

   Convert to distance

   Multiply duration by 0.0343 cm/µs and divide by two.

   Reject zero or out-of-range values.

6. Step 6

   Build a calibration lane

   Mark 10, 25, 50, 75, and 100 cm from the sensor face.

   Align the flat target square.

   Builder checkpoint: After build a calibration lane, operate the build slowly and confirm that calculated distance in centimetres begins without binding.

7. Step 7

   Collect five readings

   Average at each mark and record range.

   Pause between samples.

8. Step 8

   Test target angle

   Rotate the target 15 and 30 degrees at 50 cm.

   Explain unstable reflections.

   Builder checkpoint: At the final checkpoint, The meter reports targets from 10 to 100 cm with average error under 3 cm across five marked positions.

See the engineering

Why it works

Input

ultrasonic trigger pulse and returning echo

Output

calculated distance in centimetres

Motion

sound pulse travel-to-digital measurement

Energy losses

angled reflections, soft targets, air temperature, timing resolution

const int triggerPin=9, echoPin=10;
void setup(){ pinMode(triggerPin,OUTPUT); pinMode(echoPin,INPUT); Serial.begin(9600); }
void loop(){
  digitalWrite(triggerPin,LOW); delayMicroseconds(3);
  digitalWrite(triggerPin,HIGH); delayMicroseconds(10); digitalWrite(triggerPin,LOW);
  unsigned long duration=pulseIn(echoPin,HIGH,30000UL);
  if(duration==0){ Serial.println("No echo"); }
  else { float distanceCm=duration*0.0343f/2.0f; Serial.print(distanceCm,1); Serial.println(" cm"); }
  delay(100);
}

Make it behave

Test, troubleshoot, and tune

Keep experimenting

Try another version

Build together

Classroom and access options

Reflect on the design

1. How did target angle change the measured result?
2. Where did angled reflections affect the build most strongly?
3. What evidence shows that echo time of flight explains the motion?
4. Which change would improve calculated distance in centimetres without creating a new problem?