Yes, you read that right. An Apple IIe.

I have many retro computers and I was thinking that since the Apple II line of computers (especially the IIe) have pretty speedy serial ports that it should be somewhat simple to use an Arduino to send data to/from the Apple.

My issue is that all of my every-day computers are USB based with no RS232 serial. I guess I could boot up an old Linux laptop that has a serial port but that seems too cumbersome given my limited desk space. :-)

Anyway, I've Googled but I'm not finding anything.

Since most Apple IIe disk images are pretty small (<144k or so) they should fit pretty easily into, say, an Arduino DUE that I have. Or better yet, using the DUE to mount as a USB device that could send over to the IIe would be great.

So, my question is, does anyone know of any site that explains how this could be done?



OK, turns out it WAS pretty easy getting the Arduino DUE to send to the Apple IIe. I simply connected 3 wires from TX1/TR1/GND to the Apple IIe serial port (SSC).

Now, when I launch ADT Pro and start sending, the IIe is receiving garbage. Bunch of "9d9d9d9d" all over the place.

Here's my code:

// ADT.ino

int incomingByte = 0;

void setup() {



void loop() {

    if(Serial.available() > 0) {

        while(Serial.available() > 0) {

            incomingByte = Serial.read();




The ADT Pro software is set to send the data over the USB port and it's obviously sending data to the IIe. I'm just wondering if the formatting is wrong or something.


1 Answer 1


You need to adapt the levels. Arduino Due operates on 0 - 3.3 V. Apple IIe is either on 0 - 5 V or +/- 12 V (depends which port you are using). There are standard ICs to do the level adaptation.

  • 1
    That's important yes. But equally important to success is that the signals must be inverted. Feb 3, 2015 at 17:40
  • Yes, correct connection and correct level. Non-adaptation of the voltage level may lead to the destruction of the Arduino board. A typical chip would be in the MAX220-MAX249 series from Maxim, and many other providers have compatible chips.
    – MAC
    Feb 3, 2015 at 21:23
  • I went ahead and marked this as the answer. My mistake is not realizing the differences in TTL vs. RS232. I'm lucky I didn't fry my DUE! I have always just plugged serial cables into that DB9 connector and never really understood what it was doing (like most people). Only now, I need to know HOW it works because I want to build an SD card reader for my Apple IIe. Anyway, I have bought the correct cable/converter off eBay. In the meantime, I'm going to mess around with some MAX232 chips I have and experiment. This time, with a better understanding. :-D
    – cbmeeks
    Feb 4, 2015 at 18:18

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