TinyPS2

Features

• PS/2 keyboard or mouse to TTL Level Serial converter based on Scott Baker BLOG
• ATTiny85 8-bit CPU
  • Run at 8 MHz in this use-case
  • 8 KB of In System Programmable (ISP) flash
  • 8-MHz internal RC oscillator that can be used as the default clock
  • 512 bytes of EEPROM
  • 512 bytes of SRAM
• 115,200 baud
• 49x49mm ODAS form factor
• 4-40 mounting holes
• 3.3V or 5V operation
• Current measurement
  • 1 mA @ 5V (without keyboard)
  • 13 mA @ 5V (including keyboard)
  • 8mA @ 3.3V (including keyboard)
    • Requires a keyboard that works at 3.3V

TinyPS2 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

H2 - In-System Programming Header

• SPI connector to download ATTiny85
• 2x3 header
• Program ATTiny85 without PS/2 keyboard attached
• Pinout

1. KBCLK
2. VCC
3. SERTX
4. KBDAT
5. RST*
6. GND

Firmware

• GitHib Repo for TinyPS2 Firmware

Scott Baker's build

• Scott Baker's Build BLOG page

• Scott's GitHub page
  • Scott appears to have used Crosspack for AVR software development
• Scott uses two libraries from other projects
  • ATTiny85 UART Library - The Garage Lab
    • uart_send.c
  • Interrupts: Interfacing a Microcontroller with a PS/2 Keyboard - PS/2 Keyboard Library
• Scott has hex file
  • FUSES = -U lfuse:w:0x62:m -U hfuse:w:0xdf:m -U efuse:w:0xff:m
  • Downloaded using TL866i
  • Used Fuse bits from Programmer
    • Matched lfuse values already

Tested Scott's Build

• Works really well
• 115,200 baud
• Works at 3.3V or 5V
  • Drops out around 3.15V - may need BOD bit changed?

TinyPS2 (Arduino IDE)

• GitHub Software Repo
• Resources (Arduino UNO)

Sketch uses 850 bytes (10%) of program storage space. Maximum is 8192 bytes.
Global variables use 15 bytes (2%) of dynamic memory, leaving 497 bytes for local variables. Maximum is 512 bytes.

TinyPS2V03

• Test routine
  • Sends out A-Z in serial line at 9600 baud (~100uS bit time)
• Software Serial library
  • Verifies SoftwareSerial works

• Test with TinyPS04 sketch
  • 2 mS off/on on serial output pin verifies delay(2)
    • Caught missing bootloader (sets speed fuses)

TinyPS04

• Test with TinyPS04 sketch
• Toggle serial output line every 2 mS
• Verifies delay(2)

TinyPS05

• Intent: Verify interrupt from keyboard does not conflict with Software Serial
• Toggles serial out line if char comes in
• Never toggles

Programming Card

• Programming procedure is taken from here
• Add ATTiny Board support to Preferences, Path:

https://raw.githubusercontent.com/damellis/attiny/ide-1.6.x-boards-manager/package_damellis_attiny_index.json

• Select ATTiny85, 8 Mhz
• Burn bootloader - Otherwise clock is way off

• ATProgHead
  • Running Arduino as ISP

Other People's Videos

• Scott Baker's Build

Schematic

• Schematic

Issues

• Missing pull-up resistors on PS/2
  • Rev 2 - add pull-up resistors
  • (There's pullups in the part so this may not be needed)
• Missing C3 cap in sequence
  • Rev 2 - change C4 => C3

Assembly Sheet

• TinyPS2 Assembly Sheet