Ultrasonic Radar

Name: Ultrasonic Radar
Author: Synthiam

Ultrasonic on a servo sweeps 180°; radar shows distances and obstacles, integrates with movement panels for automatic avoidance, scriptable GetPing

Hardware Info

How to add the Ultrasonic Radar robot skill

Load the most recent release of ARC (Get ARC).
Press the Project tab from the top menu bar in ARC.
Press Add Robot Skill from the button ribbon bar in ARC.
Choose the Ultrasonic category tab.
Press the Ultrasonic Radar icon to add the robot skill to your project.

Don't have a robot yet?

Follow the Getting Started Guide to build a robot and use the Ultrasonic Radar robot skill.

How to use the Ultrasonic Radar robot skill

What this skill does: Ultrasonic Radar turns an ultrasonic distance sensor into a “scanner” by mounting it on a servo. The servo sweeps left-to-right (up to 180°) while the sensor measures distance. The radar screen shows where obstacles are, and (optionally) the skill can tell your robot to reverse/turn using your project’s Movement Panel.

Beginner Overview

This robot skill is designed for simple obstacle detection and avoidance. It combines:

Ultrasonic distance sensor (example: HC-SR04) to measure how far away an object is
Servo to rotate the sensor so it can “look” in different directions
Radar display to visualize where objects are detected
Movement Panel integration (optional) to automatically steer away from obstacles

How Ultrasonic Sensors Work (Simple Explanation)

Ultrasonic sensors use sonar—they send out a high-frequency sound “ping” and measure how long it takes for the echo to return. This is similar to how bats and dolphins sense their surroundings.

Good at: hard surfaces (walls, furniture, boxes)
Not as good at: soft or angled surfaces (fabric, curtains, cushions) because the sound can be absorbed or bounce away
Compared to infrared (IR): ultrasonic is usually less affected by sunlight and dark/black surfaces

What You Need Before You Start

An EZB connected to ARC
An ultrasonic sensor (HC-SR04 or equivalent, or EZ-Robot ultrasonic)
A servo (to sweep the sensor)
A way to mount the sensor to the servo (bracket, hot glue, 3D print, etc.)
(Optional) A Movement Panel skill in your ARC project if you want automatic avoidance

When the sensor is connected and configured, the skill will show the distance straight ahead of the sensor. When the servo sweeps, the radar display updates to show obstacles across the scan range.

Main Window

1) Radar Display

Shows detected objects as red dots in front of the robot (up to about 180° depending on your servo settings). The displayed distance values range from 0–255, representing the sensor’s reported reading.

Tip: If you see dots “stuck” on the screen from older scans, use Clear.

2) Sweep Line

The sweep line indicates where the servo is currently pointing. As the servo moves, this line rotates across the radar.

3) Clear Button

Clears the red dots from the radar display. This does not change settings; it only clears what you see on the screen.

4) Pause Checkbox

When checked, the skill stops sampling the ultrasonic sensor and stops moving the sweep servo. This is useful for testing, saving CPU/communication, or letting scripts control updates (see scripting section below).

5) Servo and Distance Values

Displays the current servo position value being sent and the most recent ultrasonic distance reading. Use this area to confirm the servo is moving and the sensor is returning readings.

Settings

1) Title Field

Sets the name of this skill in your ARC project. Important: If you use controlCommand() in scripts, changing the title also changes the name you must reference.

2) Board Index

Choose which EZB this sensor is connected to (for example, Board 0 is the first EZB in most projects).

3) Trigger Port

Select the digital port used by the Trigger (sometimes labeled “TRIG”) wire.

4) Echo Port

Select the digital port used by the Echo (sometimes labeled “ECHO”) wire.

3-wire sensors: Trigger and Echo are shared, so the Echo port must match the Trigger port.

5) Interval (ms)

How often the sensor is sampled, in milliseconds (100–60000 ms). Default is 250 ms. Smaller values update faster but use more communication/resources.

6) Servo Settings (Sweep Setup)

Choose the servo port and set the minimum and maximum positions for the sweep. These min/max values define how far left and right the sensor turns.

Min/Max positions: limit the sweep to prevent hitting the robot frame
Invert servo: reverses the sweep direction if movement looks backwards

7) Increment Speed

Controls how quickly the servo steps through the sweep (1–36, default 1). Increase this if you want the sweep to move faster.

8) Movement Options (Checkboxes)

These options let Ultrasonic Radar interact with your project’s Movement Panel skill for obstacle avoidance.

Scan only when moving forward: only scans when the robot is driving forward (reduces unnecessary scanning)
Control Movement Panel: allows the skill to command turns/reverses automatically
Reverse before turning: backs up first, then turns away from the obstacle

9) Minimum Distance Before Turn

Sets the threshold (value 1–255, default 20) that triggers avoidance. If the reading is at/under this limit, the skill will command the Movement Panel to turn (when Movement options are enabled).

10) Movement Delay (Turn / Reverse)

How long the robot should reverse and/or turn, in milliseconds (10–5000 ms, default 250 ms). These apply only when the skill is controlling a Movement Panel.

Distance Values (Important for Beginners)

The distance displayed by this skill is a 0–255 value. It is not automatically labeled as centimeters or inches. The exact value can vary based on sensor type, voltage, the surface material, and temperature.

If you need a real-world unit (cm/in), measure with a tape measure and note what value the sensor reports at known distances, then use that as your reference.

Scripting Integration (Using GetPing)

This skill can be updated from scripts using GetPing() (with the same ports you configured in the skill). If the Pause checkbox is checked, the skill will not continuously scan—but it will still update when your script calls GetPing().

Why this matters: You can keep the skill in your project for the radar display, but avoid constant sensor polling until your script needs it.

Wiring Diagram

Ultrasonic sensors commonly come in 3-wire and 4-wire versions, sometimes with a built-in voltage regulator. If your sensor includes a regulator, it typically needs Vin (6V+). If it does not include a regulator, it usually needs 5V.

3-wire Wiring (with built-in regulator)

Ground (Black) → GND
Power (Red) → Vin
Trigger/Echo (White) → Digital (D) pin (single shared pin)

4-wire Wiring (with regulator)

Ground (Black from regulator) → GND
Power (Red from regulator) → Vin
Trigger (White) → Digital (D) pin
Echo (Green) → Second Digital (D) pin

Fix Ultrasonic “False Positives” (EZ-Robot Sensor Tip)

If you are using an EZ-Robot ultrasonic distance sensor and you see occasional false readings, the ping sound may be echoing inside the sensor casing. A simple fix is placing a few cotton balls inside the case around the sensors to dampen internal reflections.

Watch the video below for step-by-step instructions.