Based on the feedback I got, I had an idea to derive an interface that can plug an Arduino Shield or an Arduino Uno into the Apple II bus using a 82C55 peripheral interface chip. By soldering stackable headers into the Apple II card, an Arduino Uno can be plugged into the back of the card, and shields can be plugged into the front of the card. There are resistors between the 82C55 and the Arduino pins to protect the Apple II and allow the transactions to be inputs or outputs. You can find the card at
It should be a fun card for anyone who wants to experiment with interfacing to an Apple II.
Great stuff Dan, keep it coming!
Arduino is a great prototyping platform. This provides a pretty excellent way to design some neat stuff for the Apple II.
I ordered boards for this, hopefully they will turn out.
Just a note. You may need to solder the 82C55 directly into the board in order to keep the profile low enough to attach an Arduino in the back. All of the 82C55 pins are protected using resistors so hopefully this should prevent damage to the 82C55 that might require replacement.
My boards came in from China.
Would it be possible for you to post a pic of the assembled board? I've got some questions about part placement on the board, like which way the stackable heaaders for the Arduino UNO goes.
Here are picture of the card. In the present version I had to cover some of the contacts with tape so that they wouldn't touch the large USB connector housing on the Arduino Uno. I moved the resistors around in the next version to avoid this problem.
Thanks, that helps a lot. I mainly wanted to make sure I had the stackable headers on the right direction. I started soldering but I'm still waiting on some of the parts and I ran out of 1k Ohm 1/4 watt resistors... So I had to order more. Also realized I didn't have the right kind of 28 pin DIP socklet so I had to order some of those too.
I'm curous also as to how well devices with similar footprint to the Arduino UNO will work like the WeMOS D1 (ESP8266) or the Esquillo (ARM M1 Cortex). Both of those have some interesting capabilities... Built in WiFi, etc.
The ROM isn't really necessary to use the card unless you want to write your own ROM. You can do what I did and use use a part of a 40 pin socket as a 28 pin socket, which is cheesy, but works. By the way, you can buy huge bags of 1k resistors on ebay which is what I did (as well as 10k) because it's such a common value.
I would recommend trying to control those using SPI bit-banged from the 82C55. I don't think UART will be reliable enough. With SPI, the communication is synchronous to the speed of the Apple bus.
I have one of these cards complete except for I'm waitning on 74HCT32 chips. I have two more almost finished, I just need the 74HCT32 and waiting on two more 82C55 chips.