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Topic: Sending keystrokes to an Apple IIe (Read 736 times) previous topic - next topic


After managing to build a board to read keystrokes on an Apple IIe keyboard and send them to a modern computer via USB, now I'm trying to tackle the job going in the opposite direction.

After some research and testing, it looks like the IIe is pulsing the "columns" pins about 20 times a second. In normal operation, a switch in the matrix keyboard connects a column to a "row" and the computer reads that as a keypress. The timing is important. If I set a row pin high, the IIe cycles through all the column combinations until the row is set low again.

So, what I've done as a proof of concept is hook up a column to pin 10 and a row to pin 8. When I trigger the keypress (in this case, by sending "a" via serial) the input value of the column pin is sent out to the row pin, and the proper letter shows up on the IIe screen. Success! (I'm leaving the USB host problem until later, most likely to be handled by a Circuits@Home shield)

Code: [Select]
void setup()
  // initialize the serial communication:
  pinMode(10, INPUT); // column
  pinMode(8, OUTPUT); // row


void loop()

   if (Serial.available() > 0) {
    // get incoming byte: 
    inByte = Serial.read();
    if(inByte == 'a') { // i typed "a"
      inputPin = 10; // set the in/out pins
      outputPin = 8;
    } else {
      inputPin = 0; // something else was typed, so set the in/out to an unused pin
      outputPin = 0;

  if(inputPin > 0) {
    val = digitalRead(inputPin);   // read the input pin
    digitalWrite(outputPin,val); // send the pulse to output
  } else {
    digitalWrite(outputPin,LOW); // stop pulsing output

To cover the whole matrix, however, there are 8 columns and 10 rows. And modifier keys (shift, control) that get read when the pin is grounded.

So, i need more pins than the ATMega328 provides - i could use a larger Arduino, but my eventual goal is to embed just the ATMega on a smaller board.

I've read here and elsewhere about ganging up inputs with a 4021 IC (shift register). Would this be a good application? I imagine I would put all the columns into one register, and when I want to trigger the key that's a combination of column 3 and row 4, I could read the third bit from the register, and pulse row 4 in time with it.

Would that work, or am I wrong about how the register works? Will I be able to read the 4021 state fast enough to pulse the row pin in time with the input?


After doing a little more looking into multiplexing, i think i've decided to try going with a TI CD74HC4067 multiplexer chip on the outputs instead of the inputs.


Any guidance on whether this should work, and if so, how reliably, would be appreciated. The main thing that worries me is the timing.



I've got the multiplexing working reading multiple pins into a single "signal" pin in my ATMega, so that's progress.

Now, I'm looking for a terminal to send it keystrokes that's a little more fully featured than the built in serial monitor in the Arduino app. I saw something in the forums recently, but I can't find it again (typical...)

Any suggestions for a serial terminal application for Mac that can send keystrokes without having to hit enter?

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