A standalone, screen-based reader and diagnostic tool for Makita LXT (18V) batteries — no PC required.

Website · Platform family · Watch it in action · Status · Features · Hardware · Build & flash · License

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It reads cell voltages, temperatures, charge count and error/lock state, and can reset false BMS lockouts to rescue packs that are still good.

PocketOBI is a standalone OBI client: it speaks the same Makita OneWire protocol documented by the Open Battery Information project, but as a self-contained handheld device with a TFT screen and a rotary encoder instead of a computer.

Created by The Repair Forge — website: https://therepairforge.github.io/ — follow the build on YouTube: https://www.youtube.com/channel/UCQL_-pcIEkrDPyljl3QPzcw

Platform family

PocketOBI started on Makita LXT (18V) — this repo — and is growing into a small family of standalone OBI-client readers, one per battery platform. Same hardware/UI approach, same protocol-first philosophy, different pack connector and decode tables under the hood.

Platform	Tag	Status
Makita LXT (18V)		✅ shipping — this repo
Makita XGT (40V)		🔜 planned
HiKOKI (BSL)		🚧 in progress

Each sibling gets its own repo once it's ready to publish; this table (and its own release badge) grows as they ship.

📺 Watch it in action

The v2 walkthrough — the new interface, the traffic-light verdict and the staged repair wizard in action: https://youtu.be/8Qe2dTXrJ8g

Original build & protocol deep-dive — how it works, the reverse-engineering, and a live demo: https://youtu.be/57KsQQ7-Qd0

Project status

Current release: see the latest release and CHANGELOG.md for details.

The v2 interface: a 2×2 launcher, a paged Battery view, a traffic-light verdict and a staged Repair wizard, multilingual EN/FR/DE/ES, on a single-source build. Validated on real BL18xx packs. Since v2.2 the same firmware also runs on the CYD (ESP32-2432S028R) with a touch UI, as an alternative board. Since v2.3 every release ships ready-to-flash binaries, and since v2.5 an Asia build shows the UI in Japanese, Korean and Vietnamese, joined by Simplified Chinese in v2.6. Since v2.6 it also runs on the ES3C28P (ESP32-S3, capacitive touch). Feedback and test reports (especially serial logs from real packs) are very welcome.

⚠️ Safety first. These packs contain lithium cells and up to ~21 V on B+. Never connect B+ to the ESP32. Resetting a BMS error only helps a pack whose cells are actually healthy (a false lockout). Do not force a pack with a genuinely bad/low cell back into service — it is a fire risk. Use this tool at your own risk.

Features

• Standalone V2 interface — a 2×2 launcher (Battery / Repair / Tools / About) driven by the rotary encoder (+ a secondary back button: short = back, long = home); the pack is read on demand, when you open Battery or Repair.
• Battery view, paged (turn the encoder): Overview / Health / Identity.
  • Overview: per-cell voltage bars (green / yellow / red), pack voltage, spread.
  • Health: our own cycle-based Condition estimate, over-discharge / over-load wear counters, cell min/max + spread, both temperature sensors + spread.
  • Identity: model, charge count, manufacturing date, capacity, and the pack serial number (ROM ID in Makita 16-char hex format).
• Traffic-light verdict — HEALTHY (green) / UNLOCK (yellow) / POSSIBLE HW FIX (orange) / HARDWARE FIX (red). One verdict, computed from a single source and shown identically on the Battery tile, the screens and the Repair wizard.
• Repair wizard — a staged, feasibility-first check: comms → hardware faults (broken sense wire / weak group / imbalance / thermistor, each naming the group or sensor) → charger lock + prognosis (a false lockout: "our unlock should hold"; a pack that re-locks after the unlock has a real fault). A hardware fault blocks the unlock; the prognosis reads as guidance, never a guarantee.
• Unlock / repair — rewrites the frame to lift a false charger lockout on a pack whose cells are healthy: clears the charger-lock nybble, recomputes the charger-validated checksums, writes the frame back. Never forces a genuinely bad pack back into service. See below.
• Error reset with before → after feedback (full test-mode + power-cycle sequence).
• Automatic detection of standard vs older F0513 BMS generations.
• Multilingual UI — English, French, German, Spanish; Japanese, Korean, Vietnamese and Simplified Chinese in the Asia build (see below).
• PC bridge mode — acts as a USB↔OneWire adapter (drop-in ArduinoOBI), so a desktop app works through PocketOBI: the original Open Battery Information app, or our own companion PackScope — saved history, a health estimate and a guided repair workflow. Dual use: standalone tester and PC adapter.
• Tools: pack LED test, error reset, raw debug view (ROM ID + message frame).

Asia build: 日本語 / 한국어 — help wanted

The Asia build of the firmware shows the whole UI in Japanese, Korean, Vietnamese or Simplified Chinese, with English kept to find your way (Settings → Language → EN / JA / KO / VI / ZH; French, German and Spanish are in the standard build). The Japanese and Korean texts are first drafts that no native speaker has reviewed: expect stiff phrasing and some wrong repair vocabulary. I read neither language, so I cannot judge them myself. The Vietnamese one was written by a Vietnamese user, without accents (the device fonts have none), and the Chinese one by a Chinese user (issue #29).

If you read Japanese or Korean and work on power tools or batteries, I would love your help. Each language is one file, strings_ja.h and strings_ko.h: one line per message, with the English next to it. Open a pull request, or an issue with corrections, no Git needed. You can see your text on every screen without a board with tools/hostsim. Rules and details: docs/TRANSLATING.md.

Build it with pio run -e esp32-c3-asia (or cyd-asia), or in the Arduino IDE by putting #define ENABLE_CJK 1, #define ENABLE_EU 0 and #define ENABLE_VI 1 in a local board_local.h next to the sketch.

Architecture

(click for full size — full-resolution file in docs/architecture.png)

From the battery up: the Makita pack speaks over a single data wire; the bundled OneWire2 driver (reused from OBI) handles the custom Makita bit timings; the ESP32-C3 firmware is layered — protocol (frames + ENABLE, pack-type detection), data decode (bytes → cells / temperature / errors / lock), display (Adafruit GFX

• ST7789) and a small UI state machine — driving the TFT and, optionally, a USB PC bridge.

Hardware

Component	Notes
ESP32-C3 SuperMini	any ESP32-C3 board with native USB
2.4" SPI TFT, ST7789 (240×320)	+ integrated EC11 rotary encoder module
Makita BL1830 LXT adapter	clips onto the 18V pack
2 × 470 Ω resistors	pull-ups for DATA and ENABLE (4.7 kΩ also works with short wiring)
USB-C power (power bank/charger)	powers the tool — NOT the battery

Wiring

(click for full size — full-resolution file in docs/wiring.png)

Display + encoder module (2-in-1 TFT + EC11):

ESP32-C3	Module pin	Role
GPIO0	SCL	SPI clock
GPIO1	SDA	SPI data (MOSI)
GPIO10	RES	reset
GPIO20	DC	data / command select
GPIO21	CS	chip select (active low)
3.3 V	VCC	logic power
3.3 V	BLK	backlight (or leave unconnected = always on)
GND	GND	ground
GPIO5	A	encoder phase A
GPIO6	B	encoder phase B
GPIO7	PUSH	encoder push button
GPIO2	KO	secondary button (short = back, long = home)

Battery adapter (Makita LXT connector):

ESP32-C3	Battery pin	Role
GPIO3 + 470 Ω pull-up to 3.3 V	Pin 2 — DATA	OneWire data
GPIO4 + 470 Ω pull-up to 3.3 V	Pin 6 — ENABLE	enable (active high)
GND	main B- terminal	ground (sturdier than signal pin 5; same ground)
—	Pin 1 — B+ (18 V)	NEVER CONNECT

Notes:

• Pull-ups: 470 Ω is the bench-validated value: on 3.3 V logic the pack loads the DATA line near the input threshold, and 4.7 kΩ was marginal with breadboard wiring. 4.7 kΩ (the upstream OBI value) should be fine with short, clean wiring. ENABLE is a driven output; 470 Ω there just keeps a single-value BOM.
• ⚠️ Identify DATA/ENABLE by the ESP32 silkscreen labels ("3" / "4"), not by the adapter's connector position. Some AliExpress adapters number their orange connector from the opposite end, so DATA can land on what looks like "plot 6" and ENABLE on "plot 2". Wrong plots = no comms (present = 0, all-FF/00).
• Power the tool from USB-C, never from the Makita pack (B+ is 18 V, and the BMS can cut its own output on error).

A carrier PCB has been fabricated and bench-validated. The fabrication files (Gerbers, schematic PDF, BOM) and ordering notes are in hardware/; the wiring and pinout reference stays in HARDWARE.md.

Alternative board: CYD (ESP32-2432S028R)

Since v2.2 the firmware also builds for the "Cheap Yellow Display" (dual-USB / ST7789 revision, XPT2046 resistive touch). Same logic, same screens; the UI is driven by touch instead of the encoder, with on-device touch calibration (Settings > Calibrate). The ESP32-C3 build above remains the reference product.

The whole pack connection fits on the CYD's 4-pin CN1 header:

CN1	Battery pin	Role
IO22 + 470 Ω pull-up to 3V3	Pin 2 — DATA	OneWire data
IO27 + 470 Ω pull-up to 3V3	Pin 6 — ENABLE	enable (active high)
GND	main B- terminal	ground
3V3	—	feeds the two pull-ups
—	Pin 1 — B+ (18 V)	NEVER CONNECT

Step-by-step guide (build, flash, wiring, first read): docs/CYD_GUIDE.md. Board selection and build notes: CYD_NOTES.md.

Alternative board: ES3C28P (ESP32-S3)

Since v2.6 the firmware also builds for the LCDWiki ES3C28P, a 2.8" ESP32-S3 board with an ILI9341V panel and FT6336G capacitive touch. Same logic and screens as the CYD, driven by touch; Settings > Calibrate is there if taps land off target. The board has a LiPo charger and a battery socket, but running it from a cell instead of USB is not tested yet (it would not show the battery level). Thanks to the community tester of discussion #22 who brought it up and tested every early build.

No single socket carries both the bus and 3.3 V, so the pack lead takes two of the board's 1.25 mm sockets: DATA and ENABLE from Expand, 3.3 V and GND from I2C (pin 1 = the triangle on the silkscreen).

ES3C28P socket	Battery pin	Role
Expand pin 1, IO2 + 470 Ω pull-up to 3.3V	Pin 2 — DATA	OneWire data
Expand pin 2, IO3 + 470 Ω pull-up to 3.3V	Pin 6 — ENABLE	enable (active high)
I2C pin 2, GND	main B- terminal	ground
I2C pin 1, 3.3V	—	feeds the two pull-ups
—	Pin 1 — B+ (18 V)	NEVER CONNECT

Leave the I2C socket's IO15 / IO16 alone: they are the touch controller's bus. Never use the UART socket's 5V for the pull-ups.

Build & flash

Flash a prebuilt binary (no build)

Easiest: the web flasher flashes the latest release over USB from Chrome or Edge on a computer, nothing to install.

Or by hand: each release carries one merged image per board and language, flashed at address 0x0:

File	Board
PocketOBI-vX.Y.Z-esp32-c3.bin	ESP32-C3 (the reference product)
PocketOBI-vX.Y.Z-cyd.bin	CYD (ESP32-2432S028R)
PocketOBI-vX.Y.Z-esp32-c3-asia.bin / -cyd-asia.bin	Same boards, Asia build (EN / JA / KO / VI, + ZH from v2.6.0; -ja up to v2.3.1)
PocketOBI-vX.Y.Z-cyd-ili9341.bin	CYD fitted with an ILI9341 panel (mirrored image on the plain CYD build, see the CYD guide)
PocketOBI-vX.Y.Z-es3c28p.bin	ES3C28P (ESP32-S3), EN / FR / DE / ES / VI, from v2.6.0

pip install esptool
esptool --chip esp32c3 write_flash 0x0 PocketOBI-vX.Y.Z-esp32-c3.bin   # ESP32-C3
esptool --chip esp32 write_flash 0x0 PocketOBI-vX.Y.Z-cyd.bin          # CYD
esptool --chip esp32s3 write_flash 0x0 PocketOBI-vX.Y.Z-es3c28p.bin    # ES3C28P

A merged image flashed this way resets the saved settings (language, flip, touch calibration): set them again afterwards. The web flasher keeps them unless you tick "Erase device". If a CYD flash stops halfway, add --baud 115200.

Older esptool versions are called esptool.py. Check a download against SHA256SUMS.txt from the same release. The parts-*.zip files hold the separate bootloader, partition table and application images for tools that want them. Release images are built by the project's CI with tools/release_bins.sh, which you can also run yourself.

Arduino IDE

1. Install the ESP32 board package (Espressif) via the Boards Manager.

   Use a stable core (3.x). PocketOBI is built and tested against the stable ESP32 core 3.x (2.0.x also works). Avoid the alpha/dev releases (e.g. 4.0.0-alpha1): they build fine but flood the console with harmless -Wdeprecated-declarations / -Wmissing-field-initializers warnings coming from the core itself (esp32-hal-ledc.c, Esp.cpp, …), not from PocketOBI. If you see those warnings, it is the alpha core, not a bug here — select a 3.x version in the Boards Manager.

2. Install these libraries via the Library Manager:

   • Adafruit GFX Library
   • Adafruit ST7735 and ST7789 Library
   • RotaryEncoder (by Matthias Hertel)
   • (OneWire2 is bundled in this repo — nothing to install.)

3. Open PocketOBI/PocketOBI.ino.

4. Board: ESP32C3 Dev Module, USB CDC On Boot: Enabled.

5. Upload.

CYD build (Arduino IDE): also install XPT2046_Touchscreen (Paul Stoffregen, v1.4), select ESP32 Dev Module, and put a board_local.h next to the sketch containing #define POCKETOBI_BOARD BOARD_CYD (the file is gitignored).

ES3C28P build (Arduino IDE): no extra library (the touch driver is in the repo). Select ESP32S3 Dev Module, USB CDC On Boot: Enabled, Flash Size: 16MB, and put #define POCKETOBI_BOARD BOARD_ES3C28P in board_local.h (add #define ENABLE_VI 1 for Vietnamese).

Note: Arduino requires the sketch to live in a folder named PocketOBI. If you downloaded a ZIP (GitHub adds a -main suffix), rename the inner sketch folder back to PocketOBI before opening it.

PlatformIO (VS Code)

The platformio.ini at the repo root builds the same sources the Arduino IDE uses, straight from the sketch folder — no separate project, no copy to keep in sync:

pio run -e esp32-c3             # build the ESP32-C3 product
pio run -e esp32-c3 -t upload   # build + flash
pio run -e cyd -t upload        # CYD alternative board
pio run -e es3c28p -t upload    # ES3C28P alternative board
pio device monitor              # serial monitor (115200)

There is one env per board; always pass -e, otherwise pio run -t upload builds and flashes every env in turn. The esp32-c3 env uses esp32-c3-devkitm-1 (works for the ESP32-C3 SuperMini); change board in that env for a different ESP32-C3 module.

Usage

Power the tool over USB and connect DATA / ENABLE / GND to the pack (never B+). It boots to the launcher: Battery / Repair / Tools / About. Turn the encoder to select, click to open; the back button goes back, a long press returns to the launcher. The footer of each screen names what the inputs do there. On the CYD and the ES3C28P: tap an item, tap the title bar to go back.

• Battery reads the pack when you open it. Turn to change page (Overview / Health / Identity), click to read again. Until a pack has been read, the launcher tile shows "NO PACK"; after a read it shows the pack voltage and the verdict.
• Repair reads the pack and shows the diagnosis. If there is a lockout to clear and no hardware fault, it asks "Unlock pack?" before anything is written: click confirms, turning cancels.
• Tools has two pages: PC bridge, Debug / raw, Settings; then Pack LEDs on, Pack LEDs off, Reset error (marked "Write": they send a command to the pack).

"Comm error" (NO RESPONSE) means the pack did not answer: check the DATA wiring, the pull-ups and GND, and re-seat the pack. A pack that never answers (all-0xFF) has a dead BMS or is not an OBI-compatible pack.

Trouble reading a pack, or connecting the PC bridge? See TROUBLESHOOTING.md — a step-by-step guide to wiring, no-comms and bridge-connection faults.

Unlock / repair

Some packs refuse to charge even though their cells are healthy and balanced: the BMS stores a frame that trips the charger's lock. The Makita charger only validates three fields of the 32-byte frame:

• nybble 34 (byte 17, low) — the charger lock, must be 0;
• CS0 (nybble 41) — sum(nybbles 0–15) & 0x0F;
• CS2 (nybble 43) — sum(nybbles 32–40) & 0x0F.

The status byte (byte 19, e.g. 0xA5) and the reported temperatures are not part of that check. The battery's own internal lock additionally checks CS1 (nybbles 16–31, per the rosvall protocol docs), so the repair recomputes all three checksums. The Unlock / repair menu entry clears nybble 34, recomputes CS0/CS1/CS2, writes the frame back (arm → write → store) and clears the internal error register. The failure code (nybble 40, e.g. 0xF = dead) is never cleared — a genuinely dead pack is not forced back into service. Manufacturing/status bytes are never touched, and if the frame is already valid no write is performed.

⚠️ This writes to the BMS flash and is gated behind a confirmation screen. It only clears a false charger lockout on an otherwise-healthy pack; it never overrides the BMS's own fault protection. Never use it to force a pack with a bad or low cell back into service.

Note on temperature units

Temperatures are decoded as 1/10 K (T_C = raw / 10 - 273.15). This is now corroborated by four independent sources: the rosvall protocol docs, the obi-esp32 encoding, and both sides of the m5din-makita fork — its reader ((raw / 10) - 273.15) and its BMS emulator ((T_C + 273.15) * 10). The original Open Battery Information app decodes the same field as Celsius x100; that appears to be the outlier. The unit is still not stated in any official Makita document, so treat the absolute value as approximate, but the 1/10 K interpretation is the well-supported one. The dependable signal is relative: the two sensors are shown side by side (e.g. 28/31, and in red when a value is implausible), so a reading that is far off or that disagrees strongly with the other flags a likely faulty thermistor.

The two sensors are reported by the BMS over the data line (there is no separate thermistor pin on the connector). The original protocol simply labels them "Sensor 1" and "Sensor 2". PocketOBI treats sensor 1 as the cell sensor and sensor 2 as the board (MOSFET) sensor, and labels them Cell/Board in that order. That identification is our own observation, not a Makita document, and the exact placement of the sensors on the BMS board is not known.

Versioning

See CHANGELOG.md. The current version is shown on the boot splash and the About screen, and defined as FW_VERSION in pocketobi.h.

Credits

• Open Battery Information by Martin Jansson — the original project that documents the Makita protocol and provides the OneWire2 library. https://github.com/mnh-jansson/open-battery-information (MIT)
• ESP32-C3 wiring reference: the obi-esp32 port by appositeit.
• Root protocol reverse-engineering: the rosvall/makita-lxt-protocol documentation (frame byte/nybble map, the three checksum ranges, per-type command sets) — the origin much of the LXT decoding traces back to.
• Unlock / frame-repair research: the synrais/Makita-LXT-Battery-Monitor-Unlocker project, which documented the frame byte map, the CS0/CS2 checksums, the charger-lock nybble and the arm/write/store opcodes. That repository ships with no license (all rights reserved), so none of its code is used here; PocketOBI's unlock feature is a clean-room reimplementation from those (unprotectable) protocol facts only, cross-checked against real battery dumps.

License

PocketOBI is licensed under the PolyForm Noncommercial License 1.0.0 — free to use, modify, and share for any noncommercial purpose (personal, hobby, repair, education, research). Commercial use requires a separate license. See LICENSE.

Bundled and reused third-party components keep their own licenses — see THIRD-PARTY.md. The bundled OneWire2 library and the upstream Open Battery Information project remain under the MIT license.

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Built by The Repair Forge