SayoDevice O3C 3-Key Hall-effect keypad boasts 8,000Hz polling rate for playing rhythm games

While searching for new products on AliExpress, I came across the SayoDevice OSU O3C, which looks very similar to other macro keyboards such as the 4xMacropad, the LILYGO TTGO T-Encoder, or the T-Keyboard-S3. However, like the TENSTAR T-Display, it sold over 10,000 pieces on Aliexpress. This warranted an investigation, and I found that it is actually a Hall-effect keypad mainly designed for rhythm and single-input games such as osu! and Geometry Dash.

The keypad features OUTEMU magnetic Hall-effect switches with rapid trigger support and a customizable actuation point as low as 0.05 mm, for extremely fast and precise keystrokes. The keyboard connects to a PC via a USB 2.0 cable and supports an 8,000 Hz polling rate for low input latency. The device includes a 0.96-inch IPS color display that can show key travel information, key press counts, or custom images and text, and the first line of the screen can be personalized with user text. The programmable rotary knob on the device can be assigned to functions such as volume control or list scrolling. Additional features include custom key mapping, customizable RGB backlighting, switch calibration, support for different magnetic switches, hot-swappable keys, and configuration via a browser-based interface with firmware updates.

SayoDevice O3C specifications:

• MCU – WCH CH32V307WCU6 RISC-V microcontroller @ 144 MHz with 128KB SRAM, 192KB+288KB flash
• Type – Programmable 3-key magnetic switch keypad / macro pad
• Keys – 3x OUTEMU pink magnetic switches (hot-swappable, customizable trigger stroke down to 0.05mm)
• Display – 0.96-inch color IPS screen shows (Key travel visualization, key press counter, customizable text or images)
• USB – USB 2.0 Type-C port with up to 8000Hz polling rate
• Misc – Programmable rotary knob for controls (can be mapped to any function)
• Dimensions – ~65 × 50 mm (approx.)
• Material – ABS plastic keycaps with laser printing

The SayoDevice O3C can be configured via a browser-based interface on the official website, eliminating the need for a dedicated driver. The web tool allows updates, calibrates the Hall-effect switches, adjusts actuation and release parameters, configures Rapid Trigger behavior, remaps keys, and customizes RGB lighting and screen content directly from the browser.

The official firmware files are also hosted on the company’s CDN. Additional guides for firmware updates and setup are also available through the r/SayoDevice wiki on Reddit, YouTube tutorials that walk through firmware updates and troubleshooting, and some GitHub repositories host modified firmware builds, although using the official firmware sources is generally recommended for stability.

The SayoDevice O3C Hall-Effect keypad can be purchased from AliExpress for $26.92 or Amazon for $36.99.

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