Line Follower 8-ch × mBlock 5 (Makeblock edition)
The Makeblock edition of the Line Follower 8-ch plugs into an RJ25 port on mBot, Ranger, Orion or MegaPi and is read with the MBC Pro Sensors extension v2 blocks. Installation and usable ports per board: Makeblock extension.
SPIKEEV3Arduino I2CmBlockMATRIXmicro:bit
Note
Units shipped before 2026-10 use the legacy extension v1.0.0 (marked "legacy" on the download page); old and new blocks are not interchangeable.
Wiring
Sensor → mBot adapter → RJ25 port on the board (S1 = host TX, S2 = host RX). UART 38400 8N1.
Reporter blocks
| Block | Returns | Id | Meaning |
|---|---|---|---|
| Pathfinder port [port] line position | -8~+8 | 01 |
which channel the line is under: −8 (far left) to +8 (far right), 0 = centre; seen from behind the robot, negative = left |
| Pathfinder port [port] fine line position | -100~+100 | 02 |
sub-channel position: −100 to +100, 0 = centre, negative = left (same sign as line position) |
| Pathfinder port [port] line width | 0~8 路 | 03 |
number of channels on the line, 0~8; 0 = no line |
| Pathfinder port [port] line segments | 0~4 | 04 |
number of separate line segments: 0 = lost, 1 = one line, ≥2 = fork / crossing |
| Pathfinder port [port] line bitmap | 0~255 bit | 05 |
bit0 = channel 1 (left) … bit7 = channel 8; 1 = that channel sees the line |
| Pathfinder port [port] last exit direction | -8~+8 | 06 |
where the line was before it was lost: −8 to +8 (negative = left); keeps the last value |
| Pathfinder port [port] threshold | 1~99 | 07 |
reflect threshold for 'on line', 1~99, default 50; set with E4 |
| Pathfinder port [port] calibration count | 0~255 次 | 08 |
number of calibrations completed since power-on (button calibrations included) |
| Pathfinder port [port] channel [1~8] reflect | 0~100 | 10~17 |
calibrated reflect of channel 1 |
| Pathfinder port [port] channel [1~8] on line? | true/false | 05 |
bit N−1 of line bitmap 05 (channel 1 = bit0, leftmost): true when that channel sees the line |
Command blocks
| Block | Id | Meaning |
|---|---|---|
| Pathfinder port [port] black line mode | E0 |
follow a black line (default); RAM only, back to the default after reset |
| Pathfinder port [port] white line mode | E1 |
follow a white line (F3 b1 = 1); RAM only, back to the default after reset |
| Pathfinder port [port] calibrate black | E2 |
store the current reading as black (sensor over the black line), ~50 ms; saved to EEPROM（F3 bit2 = 1 while running） |
| Pathfinder port [port] calibrate white | E3 |
store the current reading as white (sensor over the white surface), ~50 ms; saved to EEPROM（F3 bit2 = 1 while running） |
| Pathfinder port [port] set threshold [threshold] | E4 |
threshold 1~99 (RAM only, back to 50 after reboot); on SPIKE an out-of-range value returns failed (state 2) |
| Pathfinder port [port] 5-second auto calibration | E7 |
sweep the sensor across black line and white surface for 5 s; min/max become the references; F3 b2 = 1 meanwhile（F3 bit2 = 1 while running） |
| Pathfinder port [port] update all values | FD |
reads the whole value table into a cache (FD pack-all); reporter blocks within the next 10 ms use the cache instead of asking one by one |
Status blocks
The extension exposes each F3 bit as a boolean block:
| bit | Name | Meaning |
|---|---|---|
| b0 | ready (ready) |
always 1 |
| b1 | white line mode (whiteMode) |
1 = following a white line |
| b2 | calibrating (calibrating) |
E2/E3/E7 in progress; new calibration commands are ignored |
| b3 | line lost (lost) |
segment count = 0 |
| b4 | fork (fork) |
segment count ≥ 2 |
| b5 | mirrored (reversed) |
E9 = 1 (sensor mounted backwards, left/right mirrored) |
Packet format (for your own decoder)
| Action | Format |
|---|---|
| Read one value | 主機送 [編號] → 回 [值低][值高][編號^值低^值高] |
| Write command | 寫入命令 E0~EE：收齊參數後回 [00][00][編號] 再執行；20 ms 內沒收齊就丟棄 |
| Unknown id | [00][80][編號^0x80]（= -32768） |
| Pack all (FD) | Send [FD] → reply [AA][10][16 × int16 LE][xor], xor = AA ^ N ^ all data bytes; content = this value table in ascending id order (shared ids and commands excluded). The extension fetches it once and serves blocks from a 10 ms cache. |
| Shared ids | F0 device ID, F1 protocol version, F2 firmware version, F3 status flags |
Sources and assumptions
Generated by _build/gen-reference.mjs from _build/protocol/line8.json (single source of truth, transcribed from the 2026-10-21 protocol decisions).
- B-11：細位置 02 與線位置 01 同號（負 = 左）；v1 韌體註解寫反，程式碼同號。
- B-12：E7 五秒動態校準補回（v1 的 0x20=0x01），定案表沒列。
- SPIKE 教育版模式 0 的 byte 8~15 補 0（#65 已改，使用者保留）。
- EV3 模式 4 與模式 2 相同內容；模式 3 改壓線位元圖（#67）。
- mBlock 舊版：MBC_MBLOCK_LEGACY=1 時逐 byte 同 2026-10-21 統一後韌體，0x0B 回 1。
- Block wording follows the v2.0.0 extension generator
build_mext.js; this page is generated from the same JSON.