TinyPS2

Features

• PS/2 keyboard or mouse to TTL Level Serial converter
• ATTiny85
  • 8 KB of flash
  • 8-MHz internal RC oscillator that can be used as the default clock
  • 512 bytes of EEPROM
  • 512 bytes of SRAM
• 9600 baud
• 49x49mm ODAS form factor
• 4-40 mounting holes
• Current measurement
  • 1 mA (without keyboard)
  • 13 mA (including keyboard)

TinyPS2

Connectors

J1 - TTL Serial Connector

1. 5V
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

TinyPS2V01 (Arduino UNO)

• PJRC PS/2 library
• Read PS/2 print to screen
• Resources (Arduino UNO)

Sketch uses 3334 bytes (10%) of program storage space. Maximum is 32256 bytes.
Global variables use 377 bytes (18%) of dynamic memory, leaving 1671 bytes for local variables. Maximum is 2048 bytes.

TinyPS2V02

• Read PS/2 keyboard, write Serial (9600 baud)
• PJRC PS/2 library
• Software Serial library
• Main sketch
  • Didn't run when first tried
  • Maybe PS2Keyboard library does not work on ATTiny85?
    • Proper interrupt support for ATTiny85?
• Pin Change Interrupts on ATtiny85
• Verified KBD data, clocks are reaching ATTiny85
• Code

#include <SoftwareSerial.h>
#include <PS2Keyboard.h>

const int DataPin = 0;
const int IRQpin =  1;

#define rxPin 3
#define txPin 2

// Set up SoftwareSerial and PS/2 objects
SoftwareSerial mySerial =  SoftwareSerial(rxPin, txPin);
PS2Keyboard keyboard;

void setup() {

  pinMode(rxPin, INPUT);
  pinMode(txPin, OUTPUT);
  mySerial.begin(9600);
  
  keyboard.begin(DataPin, IRQpin);
}

void loop() {
  if (keyboard.available()) 
  {
    
    // read the next key
    char c = keyboard.read();
    mySerial.write(c);
  }
}

• Resources (ATTiny85)

Sketch uses 3126 bytes (38%) of program storage space. Maximum is 8192 bytes.
Global variables use 241 bytes (47%) of dynamic memory, leaving 271 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

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