Usb button controller

USB Button Controller

A minimal USB HID keyboard board that reads two externally wired buttons and sends keystrokes to a host computer. No drivers required — the host enumerates it as a standard keyboard.

Designed around the WCH CH552G, an 8-bit MCU with an integrated USB device controller, on-chip 24 MHz oscillator and on-chip 5 V to 3.3 V regulator. This removes the crystal, load capacitors, reset network and programming header that a comparable AVR design would need, and cuts the controller cost from roughly $4.70 to $0.31 per unit.

An interactive version is in docs/3d-viewer.html (open it in a browser).

Specifications

Design notes

USB. Both differential pairs of the USB-C receptacle are tied together so the cable works in either orientation. CC1 and CC2 each carry a 5.1 kΩ pulldown to advertise the board as a sink; without them the host supplies no power. A USBLC6-2SC6 clamps ESD on D+/D- as close to the connector as layout allows.

Button inputs. Each channel has a 4.7 kΩ pull-up so the input never floats, a 1 kΩ series resistor and a 100 nF capacitor forming a low-pass filter with a 0.1 ms time constant, and a second USBLC6-2SC6 protecting against discharge carried in on the button wiring. The filter suppresses contact bounce in hardware; firmware adds a short debounce window on top.

Programming. The CH552G ships with a USB bootloader in ROM. Holding SW1 while plugging in pulls D+ to V33 through a 10 kΩ resistor, which puts the chip into bootloader mode. No external programmer is needed.

Ground. Copper pours on both layers, stitched with vias. The pour under the USB pair is kept unbroken to hold the differential impedance steady.

Repository layout

usb-button-controller.kicad_sch     schematic
usb-button-controller.kicad_pcb     board layout
usb-button-controller.kicad_pro     project file
docs/                   isometric render and interactive 3D viewer
gerber/                 fabrication output
  *.gtl *.gbl           copper layers
  *.gts *.gbs           solder mask
  *.gto *.gbo           silkscreen
  *.gm1                 board outline
  *.drl                 drill file
  BOM_jlcpcb.csv        bill of materials with LCSC part numbers
  usb-button-controller-all-pos.csv component placement

Manufacturing

Built for JLCPCB with assembly. Upload the gerber archive, then the BOM and placement files from gerber/.

Settings: 2 layers, 1.6 mm, HASL, top-side assembly. Enable Confirm Parts Placement — KiCad and JLCPCB do not always agree on the zero-rotation reference for SOT-23 and SOP packages, and the preview is where a misoriented part gets caught.

All passives, the LED and the tactile switch are JLCPCB Basic parts. The CH552G, USB-C receptacle, USBLC6-2SC6 and screw terminal are Extended parts and carry a per-part setup fee.

Firmware

Built with ch55xduino in the Arduino IDE. Add this board manager URL:

https://raw.githubusercontent.com/DeqingSun/ch55xduino/ch55xduino/package_ch55xduino_mcs51_index.json

Install CH55x Boards, select CH552 Board, and pick a USB setting that reserves RAM for HID. Pin mapping:

A blank chip enters the bootloader on its own, so the first upload needs no button press. Later uploads are triggered automatically unless the running firmware has locked up the USB stack, in which case hold SW1 and replug.

Verification

• ERC clean
• DRC clean, zero unconnected items
• Schematic parity between board and schematic confirmed
• Netlist reviewed pin by pin against the CH552G datasheet

Not yet verified in hardware — no board has been built from these files.

License

Not yet chosen. Add a LICENSE file before sharing this publicly.