SR42 Keyboard PCB

NB: This project design is complete, but has not been prototyped for validation.

Intent

A 42-key micro keyboard designed for QMK with specific focus on ultra fast key scan rates / poll rates to make for an ideal gaming keyboard.

Progression

• See CHANGELOG.md

Case

This case is designed in conjunction with the SR42 Keyboard Case. These two projects are mutually inclusive and built as one solution.

Resources

Schematic

• PDF here

MCU PCB

• EAGLE BRD (PCB) here
• EAGLE SCH (Schematic) here

Key Switch PCB

• EAGLE BRD (PCB) here
• EAGLE SCH (Schematic) here

Beta PCB renders

Top

Bottom (Component side)

Intra-Board Connectors

You will need 3x Molex Pico-EZMate cables

	Cable	Usage
	6 way	Keyboard Matrix SPI interface
	4 way	USB connection to UBD
	3 way	ARGB to drive status & per-key LED's

Layout ideation renders

Render

Layout

Matrix coordinates (QMK & VIA)

Planned Features

• QMK / VIA build
• 1x STM32F405 STM32 CPU (ft. dual USB, one is FS, the other HS)
• 1x TS3USB221 USB 2.0 Multiplexer for USB port selection (based on akeypad )
• 1x USB3300-EZK Hi-Speed USB Host for OTG PHY pin interface
• 1x W25Q64JW 8K SPI Flash Module [Not needed, the MCU has 512K Flash]
• 1x M95640-DRE 8K SPI EEPROM Module
• 6x MC74HC589A SPI Input Shift Registers
  • No QMK key matrix, using all direct pins for faster scan rates
  • Scan via individually grounded keys on shift registers
• 2x IS31FL3746B SPI LED Matrix Drivers
  • 43x RGB LED's
  • With power on/off TPS22995H-Q1 load switchs, 1 per
• C4 (or S1) UDB USB-C by @ai03 - see here

Possible BIG issues

• With very limited PCB space, 13x IC's may not fit :( [Resolved with separate key and MCU PCB's]
• Not sure QMK can handle High Speed USB [It can, just now need to do it :( )]
• Not sure dual USB is switchable with the USB multiplexer [Needs to be coded for and tested]
  • FS USB required for Bootloader
  • HS USB required for >1KHz polling rates

 
 

Made with ❤️ by Silvino Rodrigues