# KIISU V4B (Rainwalker OÜ)

> A credit-card-sized development board with sub-GHz, NFC, RFID, infrared and Bluetooth that runs most Flipper Zero firmware.

- **Category:** Multitools
- **Availability:** Preorder
- **Price:** €95 (at store.rainwalker.ee), checked 2026-09-17
- **Good for:** Carry a wallet-sized Flipper-firmware board for sub-GHz, NFC, RFID and infrared experiments.
- **You'll need:** A microSD card, an LIR2032 cell (not CR2032) or USB power, and Flipper-compatible firmware.
- **Trade-off:** It lacks Flipper’s secret keys, so some sub-GHz protocols and U2F may not work, and it is sold as a development board rather than a finished product.
- **Page:** https://gadgets.sh/devices/kiisu-v4/

## Where to buy

| Shop | Status | Link |
|---|---|---|
| Rainwalker OÜ | Orderable | https://store.rainwalker.ee/products/kiisu-v4b?utm_source=gadgets.sh&utm_medium=referral&utm_campaign=kiisu-v4&utm_content=api |
| Lab401 | Orderable | https://lab401.com/products/kiisu?utm_source=gadgets.sh&utm_medium=referral&utm_campaign=kiisu-v4&utm_content=api |
| Rainwalker OÜ | Source repository | https://github.com/kiisu-io/kiisu4?utm_source=gadgets.sh&utm_medium=referral&utm_campaign=kiisu-v4&utm_content=api |

## Blueprint

**Schematics published.** Rainwalker publishes a schematic PDF and 3D case models (STEP/STL) for the KIISU V4B under a strongly-reciprocal open-hardware license, but no KiCad/Altium/Gerber PCB-layout source or BOM is included.

### Design files

- schematic: [KIISU V4B schematics (PDF)](https://github.com/kiisu-io/kiisu4/blob/main/kiisu%20v4b%20schematics.pdf) (PDF)
- 3d-model: [KIISU V4B 3D model (STEP)](https://github.com/kiisu-io/kiisu4/blob/main/kiisu%20v4b%20model.step) (STEP)
- 3d-model: [KIISU V4B 3D model (STL)](https://github.com/kiisu-io/kiisu4/blob/main/kiisu%20v4b%20model.stl) (STL)
- manual: [KIISU V4B manual and quick start (PDF)](https://github.com/kiisu-io/kiisu4/blob/main/kiisu%20v4b%20manual%20and%20quick%20start.pdf) (PDF)
- schematic: [Previous revision KIISU V4A schematics (PDF)](https://github.com/kiisu-io/kiisu4/blob/main/previous/kiisu%20v4a%20schematics.pdf) (PDF)

### Source repositories

- [kiisu-io/kiisu4](https://github.com/kiisu-io/kiisu4) — hardware, CERN-OHL-S-2.0, ★146

### Key parts

| Part | Role | Datasheet |
|---|---|---|
| STMicroelectronics STM32WB55RG | Main MCU (Arm Cortex-M4, BLE + 802.15.4 radio) | https://lcsc.com/datasheet/lcsc_datasheet_1912111437_STMicroelectronics-STM32WB55RGV6_C401505.pdf |
| STMicroelectronics STM32G431CB | Auxiliary MCU (Arm Cortex-M4) | https://lcsc.com/datasheet/lcsc_datasheet_2304140030_STMicroelectronics-STM32G431CBU6_C529356.pdf |
| STMicroelectronics LSM303AGR | Accelerometer/magnetometer (eCompass) | https://www.lcsc.com/datasheet/lcsc_datasheet_1810010809_STMicroelectronics-LSM303AGRTR_C126671.pdf |
| Bosch Sensortec BME680 | Gas/humidity/pressure/temperature sensor | https://www.bosch-sensortec.com/media/boschsensortec/downloads/datasheets/bst-bme680-ds001.pdf |
| GXCAS GXHTC3C | Temperature/humidity sensor | https://datasheet.lcsc.com/lcsc/2106071002_GXCAS-GXHTC3_C2837688.pdf |

_Notes:_ Verified via `gh api repos/kiisu-io/kiisu4/git/trees/HEAD?recursive=1`: schematics PDF, STEP/STL 3D models and a previous 'v4a' schematics PDF are present; no .kicad_*/.sch/.brd/gerber/BOM files anywhere in the tree. Repo license is CERN-OHL-S-2.0 (strongly reciprocal), confirmed via the LICENSE file. STMicroelectronics' own st.com datasheet pages could not be reached from this environment (connection hangs, not a genuine 404) despite being the canonical URL for these exact part numbers -- LCSC-hosted mirror PDFs used instead and confirmed with 200 responses. GXHTC3C datasheet is shared with the base GXHTC3 part (same silicon family) per LCSC.

### Raw source files

Direct links an agent or KiCad can open (the viewer on the page reads the same files).

- 3D model (STEP, 15.4 MB): [KIISU V4B 3D model (STEP)](https://raw.githubusercontent.com/kiisu-io/kiisu4/main/kiisu%20v4b%20model.step)
- 3D model (STL, 28.7 MB): [KIISU V4B 3D model (STL)](https://raw.githubusercontent.com/kiisu-io/kiisu4/main/kiisu%20v4b%20model.stl)

## Specifications

### Cores and interfaces

| | |
|---|---|
| Main and aux MCU | STM32WB55RGV6 main MCU (up to 80 MHz) and STM32G431CBU6 auxiliary MCU (up to 170 MHz) |
| Sub-GHz | CC1101 transceiver with an internal 433 MHz antenna and a pad for an external SMA antenna |
| NFC | ST25R3916 reader and emulator with a built-in antenna |
| RFID and iButton | 125 kHz RFID reader and emulator with a built-in antenna, plus iButton reader/emulator pins |
| Infrared and Bluetooth | Infrared receiver and transmitter, Bluetooth LE, and a Flipper-Zero-compatible GPIO header |

### Display, sensors and power

| | |
|---|---|
| Display | 128x64 OLED, SSD1306-compatible in SPI mode |
| Sensors | GXHTC3C temperature/humidity fitted; LSM303AGR accelerometer/compass, BME680 gas sensor and a VL53xxx ranger are user-solderable |
| Power | LIR2032 rechargeable cell (never CR2032), USB Type-C, or a user-wired external Li-ion with a MCP73831 charger |

### Firmware and compatibility

| | |
|---|---|
| Firmware | Ships pre-flashed with Kiisu firmware and can run most Flipper Zero firmware; a Kiisu fork and an aux-MCU companion firmware are published |
| Limits | It lacks Flipper Zero secret keys, so some sub-GHz protocols and U2F may not work; the maker is not affiliated with Flipper Devices |
| Schematics | V4b schematics are published as a PDF in the repository |

### Buying and licence

| | |
|---|---|
| Price and stock | €95 including VAT on the official Rainwalker store, in stock when checked on 2026-09-29 (the store prices by visitor country; an earlier reading of €330 was its UAE-dirham price). Direct US shipping was disabled when checked on 2026-09-17. |
| Field kit | A V4B(R) field kit with board, 433 MHz SMA antenna, SMA and LiPo interfaces and a keychain is listed at €469 |
| Hardware licence | Hardware design files under CERN-OHL-S v2; documentation under CC BY-SA 4.0 |

## Documentation

- [Maker documentation repository](https://github.com/kiisu-io/kiisu4)
- [README at the reviewed commit](https://github.com/kiisu-io/kiisu4/blob/340c8a0c78f4d86d2b8df69b8d3ea551057166c9/README.md)
- [V4b user manual and quick start (PDF)](https://github.com/kiisu-io/kiisu4/blob/340c8a0c78f4d86d2b8df69b8d3ea551057166c9/kiisu%20v4b%20manual%20and%20quick%20start.pdf)
- [V4b schematics (PDF)](https://github.com/kiisu-io/kiisu4/blob/340c8a0c78f4d86d2b8df69b8d3ea551057166c9/kiisu%20v4b%20schematics.pdf)
- [Licence](https://github.com/kiisu-io/kiisu4/blob/340c8a0c78f4d86d2b8df69b8d3ea551057166c9/LICENSE)
- [Official store listing](https://store.rainwalker.ee/products/kiisu-v4b)
- [Field kit listing](https://store.rainwalker.ee/products/kiisu-v4b-field-kit)
- [KIISU official site](https://kiisu.io/kiisu-v4br/)

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Source: gadgets.sh · https://gadgets.sh/devices/kiisu-v4/ · JSON: https://gadgets.sh/api/v1/devices/kiisu-v4.json