Category Archives: Teensy

Use a TRS-80 Model 100 keyboard on a PC

Over on the Color Computer mailing list, Frank Swygert (editor of American Motors Cars Magazine) mentioned a project where someone else was using a Teensy to hook an old matrix-style keyboard up to a modern PC.

A bit of Googling led me to a similar project where someone built a Radio Shack TRS-80 Model 100 keyboard interface that lets you use it on a PC via USB. This is precisely one of the things I will be doing with a Radio Shack Color Computer keyboard (also planned to use the Teensy 2.0, since it has enough I/O lines and is very inexpensive). Share and enjoy:

I have also been informed that Chris Hawks of HawkSoft has already done this, using a Raspberry Pi running a version of the MESS emulator. He created a scaled down version of MESS to emulate the Radio Shack Color Computer, then used Teensy to interface an actual CoCo keyboard to the Pi. Very cool.

Fritzing circuit designer…

I was looking at an Arduino tutorial and noticed they had a rather nice computer diagram of an Arduino, showing how to connect all the wires up for the project

I decided to check out the link for the Fritzing program that was used to make the diagram. This freely downloadable software for PC, Mac and Linux is pretty neat. You can diagram out an Arduino breadboard layout, and then turn that in to a real schematic and even PCB layout. The layout can then be exported and sent off to have boards made. I have never done anything like this before, but I am having fun experimenting…

The following picture shows something I was playing with. It doesn’t work — it was just me experimenting with some objects. But, I think this program might end up being pretty fun to play with. Check it out.

Playing with Fritzing...(Above was some initial concept work done on “yet another” joystick converter. This one will be designed to hook a modern USB joystick or mouse up to an old Tandy 1000 or Color Computer. I also plan to allow it to do the same thing with a PC keyboard to the CoCo. For emulation fans, the reverse is also planned, allowing an analog TRS-80 joystick to be hooked up to a modern computer via USB, and the same thing with a CoCo keyboard. This is going to take a bit more work than what I have done so far, but it seems pretty straight forward, once I figure out how to use switching transistors…)


Part 1b: A few more notes…

In an earlier post, I shared some source code for a Teensy 2.0 that would use digital input pins to read an Atari 2600 joystick and output USB keyboard characters in iCade format. You may notice that this source code is vastly different than the simple “first thing I ever wrote on an Arduino” I just posted. The current source code incorporates debouncing, statistics, and is easily configurable from some defines and arrays.

Over the next few posts on this subject, I will share the two versions of source that connect my first trial to the current Teensy iCade source code. I have installed a code formatting plug in to this blog which should make the code display a bit nicer. I have even gone back and hand edited the previous posts to clean up the existing source, and fix some HTML nastiness that the software I am using wasn’t smart enough to prevent.

I should also note that, while I am new with Arduino, I am not new with programming embedded devices. I used to work for a company called Microware that made an embedded, multi-user, real-time operating system called OS-9. Before I began work there in 1995, I spent my youth programming 8-bit home computers like the Tandy/Radio Shack TRS-80 Color Computer. After all these years of feeling like technology has passed me by, I suddenly find myself back in a world where a tiny micro like the Arduino (or the TI MSP430s I program on at my day job) feels right at home.

Maybe one day I will learn how to program Android and iOS apps, but until then, there are still plenty of unused bits in these tiny computers to exploit.

More to come…

Teensy 2.0 iCade source code

(Edited on 02/12/2013 to fix the source code formatting, and to add a photo.)

NOTE: There is a native method of compiling code for the Teensy, using a C compiler, but this source code was built using the Teensyduino add-on. It enables the standard Arduino IDE GUI to build code for the Teensy. You have to install the Arduino IDE first, then you install the Teensyduino add-on on top of it.

“As seen on the Teensy Project Page.”

Teensy 2.0 as an Atari 2600 joystick interface for iOS

Teensy 2.0 as an Atari 2600 joystick interface for iOS

This is my source code for the Teensy 2.0 iCade/Atari joystick interface. It could easily be made to work on an Arduino that has USB HID support (Arduino Leonardo, Esplora) and enough digital I/O pins. It is a bit bulky because I emit various status messages for testing, but I will at some point provide a stripped down version. I also have a version that uses the Debounce library which appears even smaller, but I like completely self-contained code where possible.

I have not got back to clean this up, so it includes some items commented out and such, but I wanted to provide this for those asking about it.

Or, this code could be modified to run on the new Arduino Esplora, which already has joystick buttons on it and USB HID output to act like a keyboard/mouse to whatever it’s hooked up to:

Keep in mind, the Teensy 2.0 is a low power device and it seems the 20mah of the iPad is enouhg to power it (running in low power mode, no LEDs, etc.). This may not be the case with an Arduino, and they may require hooking up via a powered hub before connecting to the iPad.


Teensy iCade Input
by Allen C. Huffman (

Monitor digital inputs, then emit a USB keyboard character mapped to an iCade
button depending on the pin status. The character will be the "hold" character
for pin connected (N.O. button push) and "release" character for pin
disconnected (N.O. button released).

Pin 11 is reserved for blinking the onboard LED as a heartbeat "we are alive"

This software was written to allow a Teensy 2.0 to interface between arcade
buttons and an iPad via USB and Camera Connector Kit.

2012-12-04 0.0 allenh - Initial version, based on my ArduinoAIDI code.

#define VERSION "0.0"
#define LED_OFF

//#include <eeprom .h>
//#include <avr/wdt.h>

iCade keyboard mappings.
See developer doc at:

   WE     YT UF IM OG
AQ< -->DC
   XZ     HR JN KP LV

Atari joystick port, looking at the male DB9 on the Atari.

 1 2 3 4 5/  Up Dn Lt Rt PA
  6 7 8 9/    Bt +5  Gd PB

  The following I/O pins will be used as digital inputs
  for each specific iCade function.
#define UP_PIN    0
#define DOWN_PIN  1
#define LEFT_PIN  2
#define RIGHT_PIN 3
#define BTN1_PIN  4
#define BTN2_PIN  5
#define BTN3_PIN  6
#define BTN4_PIN  7
#define BTN5_PIN  8
#define BTN6_PIN  9
#define BTN7_PIN  10
#define BTN8_PIN  12

  The following keys are the iCade sequence (hold, release)
  for each function. Send "W" to indicate UP, and "E" when
  UP is released.
#define UP_KEYS    "we"
#define DOWN_KEYS  "xz"
#define LEFT_KEYS  "aq"
#define RIGHT_KEYS "dc"
#define BTN1_KEYS  "yt"
#define BTN2_KEYS  "uf"
#define BTN3_KEYS  "im"
#define BTN4_KEYS  "og"
#define BTN5_KEYS  "hr"
#define BTN6_KEYS  "jn"
#define BTN7_KEYS  "kp"
#define BTN8_KEYS  "lv"

#define DI_PIN_COUNT  12   // 12 pins used.
#define DI_PIN_START  1    // First I/O pin.
#define DI_PIN_END    20   // Last I/O pin.

byte myPins[DI_PIN_COUNT] =

char iCadeKeymap[][DI_PIN_COUNT] =

char iCadeDesc[][DI_PIN_COUNT] =
  {"Up", "Down", "Left", "Right",
  "Btn1", "Btn2", "Btn3", "Btn4",
  "Btn5", "Btn6", "Btn7", "Btn8"};

/* We want a very short debounce delay for an arcade controller. */
#define DI_DEBOUNCE_MS 10 // 100ms (1/10th second)

#define LED_PIN 11
#define LEDBLINK_MS 1000


/* For I/O pin status and debounce. */
unsigned int  digitalStatus[DI_PIN_COUNT];          // Last set PIN mode.
unsigned long digitalDebounceTime[DI_PIN_COUNT];    // Debounce time.
//unsigned long digitalCounter[DI_PIN_COUNT];         // Times button pressed.
unsigned int  digitalDebounceRate = DI_DEBOUNCE_MS; // Debounce rate.

/* For the blinking LED (heartbeat). */
unsigned int  ledStatus = LOW;             // Last set LED mode.
unsigned long ledBlinkTime = 0;            // LED blink time.
unsigned int  ledBlinkRate = LEDBLINK_MS;  // LED blink rate.

unsigned int pinsOn = 0;


void setup()
  // Just in case it was left on...

  // Initialize the serial port.

  // Docs say this isn't necessary for Uno.
  //while(!Serial) { }


  // Initialize watchdog timer for 2 seconds.

  // Pins default to INPUT mode. To save power, turn them all to OUTPUT
  // initially, so only those being used will be turn on. See:
  for (int thisPin=0; thisPin < DI_PIN_COUNT; thisPin++ )
    pinMode(thisPin, OUTPUT);

  // Disable Unused Peripherals
  ADCSRA = 0;

  // Initialize the pins and digitalPin array.
  for (int thisPin=0; thisPin < DI_PIN_COUNT; thisPin++ )
    // Set pin to be digital input using pullup resistor.
    pinMode(myPins[thisPin], INPUT_PULLUP);
    // Set the current initial pin status.
    digitalStatus[thisPin] = HIGH; //digitalRead(thisPin+DI_PIN_START);
    // Clear debounce time.
    digitalDebounceTime[thisPin] = 0;
    //digitalCounter[thisPin] = 0;

  // Set LED pin to output, since it has an LED we can use.
  pinMode(LED_PIN, OUTPUT);



void loop()
  // Tell the watchdog timer we are still alive.

#ifndef LED_OFF
  // LED blinking heartbeat. Yes, we are alive.
  if ( (long)(millis()-ledBlinkTime) >= 0 )
    // Toggle LED.
    if (ledStatus==LOW)  // If LED is LOW...
      ledStatus = HIGH;  // ...make it HIGH.
    } else {
      ledStatus = LOW;   // ...else, make it LOW.
    // Set LED pin status.
    if (pinsOn==0) digitalWrite(LED_PIN, ledStatus);
    // Reset "next time to toggle" time.
    ledBlinkTime = millis()+ledBlinkRate;

  // Check for serial data.
  if (Serial.available() > 0) {
    // If data ready, read a byte.
    int incomingByte =;
    // Parse the byte we read.
      case '?':


  // Loop through each Digital Input pin.
  for (int thisPin=0; thisPin < DI_PIN_COUNT; thisPin++ )
    // Read the pin's current status.
    unsigned int status = digitalRead(myPins[thisPin]);

    // In pin status has changed from our last toggle...
    if (status != digitalStatus[thisPin])
      // Remember when it changed, starting debounce mode.
      // If not currently in debounce mode,
      if (digitalDebounceTime[thisPin]==0)
        // Set when we can accept this as valid (debounce is considered
        // done if the time gets to this point with the status still the same).
        digitalDebounceTime[thisPin] = millis()+digitalDebounceRate;

      // Check to see if we are in debounce detect mode.
      if (digitalDebounceTime[thisPin]>0)
        // Yes we are. Have we delayed long enough yet?
        if ( (long)(millis()-digitalDebounceTime[thisPin]) >= 0 )
            // Yes, so consider it switched.
            // If pin is Active LOW,
            if (status==LOW)
              // Emit BUTTON PRESSED string.
              Serial.print(" pressed  (sending ");
              Serial.println(" to iCade).");
#ifndef LED_OFF
              digitalWrite(LED_PIN, HIGH);
            } else {
              // Emit BUTTON RELEASED string.
              Serial.print(" released (sending ");
              Serial.println(" to iCade).");
              if (pinsOn>0) pinsOn--;
              if (pinsOn==0) digitalWrite(LED_PIN, LOW);
            // Remember current (last set) status for this pin.
            digitalStatus[thisPin] = status;
            // Reset debounce time (disable, not looking any more).
            digitalDebounceTime[thisPin] = 0;
        } // End of if ( (long)(millis()-digitalDebounceTime[thisPin]) >= 0 )

      } // End of if (digitalDebounceTime[thisPin]>0)
    else // No change? Flag no change.
      // If we were debouncing, we are no longer debouncing.
      digitalDebounceTime[thisPin] = 0;
  } // End of (int thisPin=0; thisPin < DI_PIN_COUNT; thisPin++ )


void showHeader()
  int i;
  // Emit some startup stuff to the serial port.
  Serial.print("iCadeTeensy ");
  Serial.println(" by Allen C. Huffman (");
  Serial.print(" DI Pins (");
  for (i=0; i<DI_PIN_COUNT; i++)
    Serial.print(" ");
  Serial.print("), ");
  Serial.println("ms Debounce.");


void showStatus()


void showDigitalInputStatus()
  Serial.print("DI: ");

  for (int thisPin=0; thisPin < DI_PIN_COUNT; thisPin++ )
    // Read the pin's current status.
    Serial.print(" ");
    //Serial.print(" (");
    //Serial.print(") ");


// End of file.

Hook an Atari 2600 joystick up to an iPad, thanks to Teensy 2.0

  • 2014/03/16 Update: The source code to this is now on GitHub. Check the Arduino link at the top of each page of this site.

“As seen on the Teensy Project Page.”

I recently gained some experience using Arduinos to control inputs in a local haunted house attraction, and that has opened up quite a world of projects. During my research, I learned about the Teensy 2.0, a cheap (starting at $16, controller that is similar to Arduino, but had more I/O pins than the Arduino Uno, plus had the ability to act like a USB keyboard or mouse. This enables it to send keystrokes or mouse movements/clicks to a computer, as if it were receiving them from an input device.

So, using the $19 version of Teensy 2.0 (that has header pins) and some wires, I was able to connect my Atari Flashback 2 joystick to an iPad via the USB adapter. I wrote a small program that reads the I/O pins of the Teensy 2.0, then sends out USB keyboard commands that emulate the iCade arcade controller.

My project was noted on the Teensy 2.0 project page:

I will be posting full notes and the code as soon as I have a moment to work on it.