TinyPS2

See TinyPS2 Revs 1-3 for ATTiny85 based build

Introduction

It is getting difficult to find ASCII serial keyboards for use in Retro-Computer projects. This card fills that need. The card is a PS/2 keyboard to TTL Level Serial adapter. PS/2 keyboards are still widely available.

Features

• QT Py (RP2040 based)
  • Run at 125 MHz
  • 2MB of In System Programmable (ISP) flash
  • 264KB of SRAM
• 115,200 baud serial
  • 57,600-250,000 are build time options
• 49x49mm ODAS form factor
• (4) 4-40 mounting holes
• 3.3V or 5V operation
• Current measurement
  • TBD @ 5V (without keyboard)
  • TBD @ 5V (including keyboard)
  • TBD @ 3.3V (including keyboard)
    • Does not require a keyboard that works at 3.3V

CPU Connections

Connectors

J1 - TTL Serial Connector

1. VCC (pin nearest to J1 silkscreem)
2. SERTX
3. N/C
4. GND

J2 - PS/2

• Standard PS/2 Mini-DIN-6 connector

Firmware Build Card Rev 4

• Card rev 4 uses a QTPy or XAIO RP2040 CPU
• Arduino Library
  • PS2KeyAdvanced
• Example code built with warning

WARNING: library PS2KeyAdvanced claims to run on avr, sam, samd1, stm32, esp32 architecture(s) and may be incompatible with your current board which runs on rp2040 architecture(s).
Sketch uses 82336 bytes (0%) of program storage space. Maximum is 16777216 bytes.
Global variables use 43096 bytes (15%) of dynamic memory, leaving 227240 bytes for local variables. Maximum is 270336 bytes.

• CircuitPython support issues
  • PS/2 Library - Not in Pico core modules

>>> import ps2io
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: no module named 'ps2io'

Schematic

• Schematic

Issues

• [[TinyPS2_Revs_1-3|Revs 1-3 are documented here]

Rev 4

• Changed CPU
  • Was 8 MHz ATTiny85
  • Changed to QT PY or XAIO
• Changed pin usage
• Uses Hardware Transmitter in CPU
• Keyboard runs at 5V
• CPU runs at 3.3VV
• 3.3V to 5V level shifter

Assembly Sheet

• TinyPS2 Rev 3 Assembly Sheet
• TinyPS2 Rev 1 Assembly Sheet