Displays HC-SR04 ultrasonic distance readings in ARC; scriptable via GetPing(), pausable, sets a variable with multiplier, optional NMS output
Hardware InfoHow to add the Ultrasonic Distance 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 Distance 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 Distance robot skill.
How to use the Ultrasonic Distance robot skill
What this skill does NOT do: It does not automatically steer, stop, or avoid obstacles. For navigation/avoidance, use the Ultrasonic Radar skill.
Ultrasonic sensors measure distance using sonar (sound navigation ranging)—they send out a quick burst of sound and listen for the echo. The time it takes for the echo to return is used to estimate how far away an object is. This is similar to how bats and dolphins “see” with sound.
Good to Know (Beginner Tips)
- Works well on hard surfaces (walls, wood, plastic, boxes).
- Less reliable on soft or angled surfaces (fabric, carpet, curtains, plush items) because they absorb or deflect the sound.
- Unlike many IR sensors, ultrasonic sensors are generally not affected by sunlight or black materials.
- Temperature and voltage can affect readings (sound travels differently in warm vs. cold air).
When an HC-SR04 (or equivalent) Ultrasonic Distance Sensor is wired to your EZB and configured in this skill, the skill will display a distance value for whatever is directly in front of the sensor.
How Readings Work (Important)
The value shown by this skill is typically 0–255. This number is a raw sensor value and is not automatically “cm” or “inches”. The raw value can vary depending on the sensor model, input voltage, the surface you’re detecting, and even room temperature.
Main Window
What You See
1. Ultrasonic Distance Value
- Shows the current distance reading (usually 0–255).
- Higher/lower values represent farther/closer objects depending on sensor and configuration.
2. Bar Display
- A quick visual way to see changes in distance without watching the number.
- Helpful for testing wiring and sensor direction (point it at a wall and move closer/farther).
3. Pause Checkbox
- When checked, the skill stops continuously sampling the sensor.
- This is useful if you only want readings on demand from a script (see next section).
Using This Skill with Scripts (GetPing)
This skill integrates with ARC scripting. If the Pause checkbox is checked, the skill will not constantly poll the sensor.
Instead, it will update when your script calls GetPing() (as long as the skill’s configured ports match your wiring).
Why pause + GetPing() is useful
- Reduces unnecessary communication traffic to the EZB.
- Lets you control exactly when a reading is taken (for example, only when the robot is moving forward).
- You can keep the skill paused permanently and still see updated values whenever
GetPing()is called.
Settings
Sets the name shown on the skill’s window. You can rename it to match where it’s installed (example: “Front Ultrasonic”).
Note: Changing the title also changes the name used in the controlCommand() reference for this skill.
Choose which EZB you are using (example: EZB #0). If you only have one EZB connected, it is usually 0.
- Trigger port: the digital pin used to send the ultrasonic “ping”.
- Echo port: the digital pin used to listen for the returning echo.
- 3-wire sensors: some combine trigger/echo into one signal wire—when using that type, set Echo to the same port as Trigger (as required by the sensor design).
Controls how often the skill samples the sensor (in milliseconds). Range: 100–60000 ms. Default: 250 ms.
- Smaller number = faster updates (more frequent readings).
- Larger number = fewer updates (less traffic and CPU usage).
Variable
- Stores the most recent reading into a variable automatically.
- This can reduce the need to call
GetPing()repeatedly, which can add unnecessary communication overhead.
Multiplier
- Scales the raw value into a more useful unit.
- Example: the default multiplier of 1.25 is commonly used to convert the reading into centimeters (depending on the sensor and setup).
- For best accuracy, calibrate: measure a known distance with a tape measure, compare to the raw value, then adjust the multiplier until it matches.
Optionally pushes distance data into the NMS (Level #3, Group #1) so other navigation skills (such as The Navigator) can use it. If you are new, you can leave this disabled until you start working with navigation behaviors. Use the ? help icons in ARC and the NMS manual for details on each option.
Wiring Diagram
Ultrasonic distance sensors commonly come in two styles: 3-wire (trigger+echo combined) and 4-wire (separate trigger and echo). Some versions include a voltage regulator (inline or built-in).
If your ultrasonic sensor has a regulator, it typically needs +6V or higher (often connected to Vin).
If it does not have a regulator, it typically needs +5V.
3-wire Wiring (with built-in regulator)
- Ground: Black wire to GND
- Power: Red wire to Vin
- Trigger/Echo: White wire to a Digital pin
4-wire Wiring (with regulator)
- Ground: Black wire from regulator to GND
- Power: Red wire from regulator to Vin
- Trigger: White wire to a Digital pin
- Echo: Green wire to a second Digital pin
Beginner Troubleshooting Checklist
- No reading / stuck value: confirm GND and power wiring, then confirm the configured digital ports match where you plugged in trigger/echo.
- Reading seems random: try changing the Interval to a slower value (e.g., 500–1000 ms), and test with a flat wall 30–100 cm away.
- Always detects “something”: check for nearby surfaces that could reflect sound (robot body panels, brackets), and see the “Fix Resolution” section below.
- Inconsistent on fabric: test with a hard surface; fabric often absorbs sonar.
Fix Resolution (False Positives on Some Housings)
If you use an EZ-Robot ultrasonic distance sensor, you may occasionally see false positives caused by the ping echoing inside the sensor casing. A common fix is placing a few small cotton balls inside the case around the sensors to dampen internal reflections.
Tech Details (Video)
Resources
Synthiam’s ultrasonic hardware reference design is available here.
Related Tutorials
Related Robots
Related Questions
Wire Length For The EZB Ultrasonic Sensor
How Do I... Not Be Hopelessly Lost?
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That would be great m8 , i am using a seperate arduino leonardo though , not the on board one does that make a diference ? i do have a microbit woud lthat support it just for testing ?
Does not look like the microbit has support for it either. The arduino uno does though: https://synthiam.com/Firmware/Delicious-Arduino-Uno-MMNJADDIIPY
Ok, i may jusy wait till you sort the leonardo firmware if thats ok , can you advise when its sorted plz
Ya my Latte Panda is also half Leonardo along with Win10 but I have yet to use it for any Arduino programs The Win10 is just so much easier to use with all my Io Tiny controllers where all sensors work instantly and programming is done in minutes instead of days with Arduino coding.
Any updates on the firmware to get sonars working on the arduino yet ? pretty please :-)
Thanks
I published the changes in the next build so it will go out when the build is published. I think it’s schedule for early next week
Is this now working on arduino ? has the build been updated
Thanks
Ironically I see the update scheduled for this evening