Pathfinder 16-Way (Line16) × EV3 × EV3 Classroom

This page covers EV3 Classroom (Scratch blocks) only: how to set it up for the Pathfinder 16-Way (Line16) on MINDSTORMS EV3, how to read every value, the commands it supports and examples. Use the switcher above to change product, host or software.

Setup

What you need

• Sensor: Pathfinder 16-Way (Line16) (EV3 edition, RJ12 plug). A SPIKE edition is not recognised on an EV3.
• Brick: LEGO MINDSTORMS EV3.
• Cable: the standard cable in the box, or an original LEGO EV3 cable.
• Software: LEGO MINDSTORMS EV3 Classroom (Scratch-style blocks, the same as SPIKE). The easiest start for first-time EV3 users.

Install the software

1. Install EV3 Classroom from the LEGO Education download page.
2. To open an example: download the .lmsp file → "Open" on the EV3 Classroom home screen → connect the EV3 → "Download and Run" at the bottom right.

Make the software see the sensor

No extension and no driver needed. On the EV3 the sensor emulates an original LEGO sensor (most products show up as an "Infrared Sensor"); use the built-in sensor blocks.

• Classroom blocks look like Scratch, but the modes are exactly the same as in the official EV3 software: Proximity / Beacon / Remote, with the same ranges. See the readings below.
• Some products come with MBC My Blocks. They are already inside the example projects; open an example and they are there.

Important

Do not switch modes in the middle of a program. Every time the EV3 switches a sensor mode it stalls for about 1 s. Pick one mode at the start and use it for the whole run.

Wiring

1. Plug the sensor into EV3 port 1 with the cable (any of 1~4 works; choose the same port in the blocks).
2. Turn the EV3 on first, then plug in the sensor.
3. Latch up, push the plug in gently.

Calibrate first (only once)

The Pathfinder has to "learn" the black and white of your mat before its numbers are right. Calibration is stored in the sensor and survives power-off (until you change mats).

1. Plug in the sensor and turn the hub on (the sensor lights come on).
2. Hold the calibration button for about 0.5 s, then release it (do not keep holding it; holding it keeps restarting calibration).
3. When the green calibration LED (next to the button) lights up, sweep the sensor back and forth between the black line and the white floor within 5 seconds. All 16 sensing points must pass over the darkest black line and the brightest white area.
4. Keep the sensor 3~12 mm above the surface while sweeping; higher reads poorly.
5. The green LED goes off = calibration done, saved in the sensor automatically.

How do I know it worked? On the white floor the "line width" is 0; on a normal black line it is 3~5.

Proximity mode: line position

Beacon mode: 16 reflected-light values

Read the "value list" (8 bytes). Each channel is quantised to 19 (1 = darkest, 9 = brightest) and two channels are combined into one two-digit number (1199), getting around the EV3 limit of 100.

Example: a byte reads 83; the tens digit 8 is the even channel (e.g. channel 0), the units digit 3 is the odd channel (e.g. channel 1).

Remote mode: position + width + edges (recommended for competition)

Read the "value list" (4 bytes):

Tip

When bytes 2 and 3 are both below 20, the front of the robot is fully on the cross line of a junction; a sudden change on one side means a fork is coming. Useful to avoid losing the line.

MBC My Blocks

The example project contains three My Blocks; no extension pack to install. Each one decodes the data in the background and stores it in its own variables. Put them inside a "forever" loop to always have the latest data:

1. LinePos16_dataUpdate: basic line following; updates 0_LinePos16 (-16 ~ +16, left negative, right positive). Good for beginners.
2. LinePos100_dataUpdate: high precision (needs a proper calibration); updates 0_LinePos100 (-100 ~ +100), 0_LineWidth16 (0 ~ 16) and the far-left / far-right edge light values.
3. LineCh16_dataUpdate: full array; updates s1 to s16, 16 variables matching each sensor from left to right.

Example program

• Classroom example (.lmsp): open with EV3 Classroom.

Want to learn more advanced line following?

These coaches have plenty of competition and teaching experience: Coach LegoLauXiao (demo video), Coach legolaumo (demo video).

First test

1. Download the .lmsp of example 1 on this page, open it, connect the EV3 and press "Download and Run".
2. If the number on the EV3 screen changes with what is in front of the sensor, everything is connected.

FAQ

• The number never changes? Unplug the sensor and plug it back in (the EV3 must be on first).
• Some examples have no Classroom version? Examples marked "Pybricks / EV3 MicroPython / clev3r only" use a mode the Classroom blocks cannot read.
• The program hiccups now and then? It switches sensor modes; each switch costs about 1 s. Use one mode only.

Reading values

The EV3 sees a stock LEGO sensor; read it with the stock Classroom sensor blocks.

line position linePos

Range	Meaning
-16~+16	which channel the line is under: −16 (far left) to +16 (far right), 0 = centre; seen from behind the robot, negative = left (normally ±15; ±16 only for 200 ms after the line leaves the outermost channel)

Value	Block	Decode	Mode
line position	Infrared Sensor → Proximity	the value	mode 0

fine position linePosFine

Range	Meaning
-100~+100	sub-channel position: −100 to +100, 0 = centre, negative = left (same sign as line position)

Value	Block	Decode	Mode
fine position	Infrared Sensor → Remote, channel 1	the value	mode 2

line width lineWidth

Range	Meaning
0~16 路	number of channels on the line, 0~16; 0 = no line

Value	Block	Decode	Mode
line width	Infrared Sensor → Remote, channel 2	the value	mode 2

channel 1~16 reflect light

Range	Meaning
0~100	calibrated reflect of channel 116, 0100 (channel 1 = left); ids 10~1F

Value	Block	Decode	Mode
#1	Infrared Sensor → Beacon heading, channel 1	the value	mode 1
#2	Infrared Sensor → Beacon proximity, channel 1	the value	mode 1
#3	Infrared Sensor → Beacon heading, channel 2	the value	mode 1
#4	Infrared Sensor → Beacon proximity, channel 2	the value	mode 1
#5	Infrared Sensor → Beacon heading, channel 3	the value	mode 1
#6	Infrared Sensor → Beacon proximity, channel 3	the value	mode 1
#7	Infrared Sensor → Beacon heading, channel 4	the value	mode 1
#8	Infrared Sensor → Beacon proximity, channel 4	the value	mode 1

Not readable here：line segments, line bitmap, last exit direction, threshold, calibrations done. Use Pybricks / clev3r for these.

Commands

The EV3 port is read-only, so this software cannot send commands: calibrate with the button on the sensor and change settings over Arduino I2C, mBlock or micro:bit.

Examples

Example 1: See where the line is

What this example does: Put the sensor over the black line and the EV3 screen shows a number telling you where the line is. This is step one of every line-following program: learn to "read the number".

What you need:

• EV3 brick + Education base robot (left wheel on B, right wheel on C)
• Pathfinder 16-way (EV3 edition, RJ12 plug)
• A white mat with a black line (about 2 cm wide)

How to connect: Pathfinder 16-way in port 1, mounted under the front of the robot about 1 cm above the ground, facing straight down.

Download the program (pick your software):

⬇ EV3 Classroom

Step by step:

1. Clear the screen first
2. Repeat the steps below forever
   • Read the line position and show it on screen row 1
   • Wait 0.1 s before the next read so the number does not flicker

What you should see: With the black line in the middle of the sensor the screen shows 0; move the line left and the number goes negative, move it right and it goes positive, up to ±16 at the edges (left/right as seen standing behind the robot, facing forward).

FAQ:

• The line is gone but the number stays at the last value? That is normal: when the line leaves the sensor, the position stays where it was last seen. To detect "line lost", use the line width from example 4 (width = 0).
• The number never changes? Check that the sensor light is on and the cable is seated. Turn the EV3 on before plugging in the sensor, or unplug and plug it back in.
• The robot steers the wrong way and gets worse? Swap the "+" and "−" in the program (swap the left/right wheel corrections), or check that the left wheel is on B and the right wheel on C.

Example 2: Three-way line following: left, right, straight

What this example does: Use "if … then … else" to make the robot follow the black line: turn left when the line is to the left, turn right when it is to the right, go straight when it is in the middle.

What you need:

• EV3 brick + Education base robot (left wheel on B, right wheel on C)
• Pathfinder 16-way (EV3 edition, RJ12 plug)
• A white mat with a black line (about 2 cm wide)

How to connect: Pathfinder 16-way in port 1, mounted under the front of the robot about 1 cm above the ground, facing straight down.

Download the program (pick your software):

⬇ EV3 Classroom

Step by step:

1. Keep checking the line position
   • If the line position is less than -4 (line is to the left)
     • Line to the left: left wheel slow, right wheel fast, the robot steers left
     • Otherwise:
       • Otherwise, if the line position is greater than 4 (line is to the right)
         • Line to the right: left wheel fast, right wheel slow, the robot steers right
         • Otherwise:
           • Line in the centre: both wheels the same speed, go straight

What you should see: The robot wobbles left and right along the black line. On sharp bends it may run off; try lowering 40 and changing 10 to 0.

FAQ:

• The number never changes? Check that the sensor light is on and the cable is seated. Turn the EV3 on before plugging in the sensor, or unplug and plug it back in.
• The robot steers the wrong way and gets worse? Swap the "+" and "−" in the program (swap the left/right wheel corrections), or check that the left wheel is on B and the right wheel on C.

Example 3: Proportional line following: the further off, the harder it turns

What this example does: Three-way line following keeps wobbling. This example uses "line position × a number" as the steering power: a little off means a little turn, a lot off means a big turn, so the robot drives more smoothly.

What you need:

• EV3 brick + Education base robot (left wheel on B, right wheel on C)
• Pathfinder 16-way (EV3 edition, RJ12 plug)
• A white mat with a black line (about 2 cm wide)

How to connect: Pathfinder 16-way in port 1, mounted under the front of the robot about 1 cm above the ground, facing straight down.

Download the program (pick your software):

⬇ EV3 Classroom

Step by step:

1. Repeat forever
   • Steering power turn = line position × 2
   • Left wheel = 30 + turn, right wheel = 30 − turn: the robot steers towards the line

What you should see: The robot follows the black line more smoothly than in example 2. The number 2 is the "proportional gain": too big and it swings left and right, too small and it cannot make the bends. Tune it yourself.

FAQ:

• It keeps swinging even on a straight line? Lower 2 a little (for example 1).
• The number never changes? Check that the sensor light is on and the cable is seated. Turn the EV3 on before plugging in the sensor, or unplug and plug it back in.
• The robot steers the wrong way and gets worse? Swap the "+" and "−" in the program (swap the left/right wheel corrections), or check that the left wheel is on B and the right wheel on C.

Example 4: Stop at a crossing

What this example does: The sensor also tells you "how many channels see the black line" (line width). Normally that is 2~3; at a crossing it suddenly jumps. This example follows the line while watching the width, and stops with a beep when it is 10 or more.

What you need:

• EV3 brick + Education base robot (left wheel on B, right wheel on C)
• Pathfinder 16-way (EV3 edition, RJ12 plug)
• A black-line mat with crossings

How to connect: Pathfinder 16-way in port 1, mounted under the front of the robot about 1 cm above the ground, facing straight down.

Download the program (pick your software):

⬇ EV3 Classroom

Step by step:

1. Keep following the line until the line width is 10 or more (reached a crossing)
   • Steering power turn = line position (-100~100) × 0.3
   • Same proportional line following, slowed down to 25
2. Stop
3. Beep to tell you it arrived

What you should see: The robot follows the line and stops with a beep when it reaches a crossing.

FAQ:

• It stops before the crossing? Bends can also widen the line; raise 10 a little.
• It does not stop at the crossing? Show the line width the way example 1 does, read the real value at the crossing, then change 10 in the program.
• The number never changes? Check that the sensor light is on and the cable is seated. Turn the EV3 on before plugging in the sensor, or unplug and plug it back in.
• The robot steers the wrong way and gets worse? Swap the "+" and "−" in the program (swap the left/right wheel corrections), or check that the left wheel is on B and the right wheel on C.

Example 5: Count crossings: stop at the 3rd one

What this example does: Competitions often say "drive to the Nth crossing". This example counts crossings with a variable count and uses another variable onCross to remember "am I on a crossing right now", so one crossing is not counted many times.

What you need:

• EV3 brick + Education base robot (left wheel on B, right wheel on C)
• Pathfinder 16-way (EV3 edition, RJ12 plug)
• A black-line mat with 3 or more crossings

How to connect: Pathfinder 16-way in port 1, mounted under the front of the robot about 1 cm above the ground, facing straight down.

Download the program (pick your software):

⬇ EV3 Classroom

Step by step:

1. Crossing counter count starts at 0
2. onCross = 0 means "not on a crossing right now"
3. Keep following the line until 3 crossings have been counted
   • Proportional line following: turn = line position × 0.3
   • Left wheel = 25 + turn, right wheel = 25 − turn
   • If the line width is 10 or more (on a crossing)
     • and we were not on a crossing a moment ago
       • Just reached a new crossing: add 1 to count
       • Remember "on a crossing" so the same crossing is not counted again
       • Beep
     • Otherwise:
       • Left the crossing: set onCross back to 0, ready for the next one
   • Show how many crossings have been counted
4. Stop

What you should see: Every crossing beeps once and adds 1 on the screen; the robot stops at the 3rd crossing. Change the 3 to stop at a different crossing.

FAQ:

• One crossing is counted twice? Happens when the black line at the crossing is damaged or shiny. Slow the speed 25 down or raise the width threshold.
• The number never changes? Check that the sensor light is on and the cable is seated. Turn the EV3 on before plugging in the sensor, or unplug and plug it back in.
• The robot steers the wrong way and gets worse? Swap the "+" and "−" in the program (swap the left/right wheel corrections), or check that the left wheel is on B and the right wheel on C.

Note

These examples have no version for this software: Example 6: Line bitmap: draw an LED ruler on the screen

More questions

• The EV3 shows an infrared sensor? Expected: the sensor emulates a LEGO sensor so the stock blocks can read it.
• A short freeze when switching modes? The EV3 needs about 1 s per mode change. Stick to one mode during a run.

Still stuck? Contact us with your software and a screenshot of the program.

Downloads

• Download centre (libraries, firmware, catalogue for every product)

Sources

• Host and software list：_build/guides.json
• Values and commands：_build/protocol/line16.json (single source of truth)
• Setup：_build/guides/software/ev3-classroom.en.md、_build/guides/product/line16/ev3-classroom.en.md
• Examples：sensors/line16/ev3-examples.md