erikarn / apple-ii-tape-interface Goto Github PK

This is an implementation of a digital cassette playback device for the apple-ii.

It implements a simple binary block protocol to wrap up data dumps of cassette data and generates the audio necessary to play it back to the apple-ii.

Yes, instead of storing .wav files, this just stores binary data dumps, a few tens of kilobytes each.

This is inspired by the TZXDuino project!

The audio itself is generated inside the Timer1 ISR. It handles generating the header, sync and data audio patterns. They're all under 2KHz so it's not a huge stretch to do it, but it does require some pretty tight timing.

The data files are stored in a binary TLV (type length value) format. The TLV headers describe the data itself, how long the header tone should be, and any pre and post playback pauses needed before a subsequent block.

Since the apple-ii doesn't have its own header binary format like the Amstrad CPC and Commodore 64 does, the user is required to provide load addresses - or it needs to be a BASIC program. BASIC records two data records - one as a short header describing the subsequent data, and then the subsequent data.

The UI is four push buttons and a 16x2 i2c connected LCD. Data is stored on a FAT formatted SD card. This currently doesn't support directories, so stick your files in the root directory of the flash drive.

I'll eventually make a schematic. But honestly, it's pretty simple. The pins themselves are described in config.h !

• An arduino nano
• D2 is the speaker output - put a 3.9k resistor between it and the audio output jack, and then a 1k resistor between the audio jack and ground. This 3.9k and 1k resistor forms a voltag divider that should deliver around 1v peak to peak of audio.
• The four buttons (PLAY, STOP, PREV, NEXT) are wired to ground. The software configures the input pins with a pull-up. Wire D3 to PLAY, D4 to STOP, D5 to PREV, D6 to NEXT.
• The SD card is an Adafruit SPI SD card - MOSI on pin 11, MISO on pin 12, SCK on pin 13, CS/SS on pin 10. No card detect is currently used.
• The i2c 16x2 LCD hooks up to the i2c pins - SDA on A4, SCL on A5.

And that's it!

The four buttons are:

• PLAY - select a tape / display its load info; a second button press will begin playback.
• STOP - stop an active playback.
• PREV - select the previous tape.
• NEXT - select the next tape.

Debugging is output over the USB / serial port at 115200 baud.

I'll document the data format in docs/tape_format.txt.

The cnv tool is in src/cnv/ . It's a simple C program.