Espple - ESP8266 Apple 1 emulator with RF out
Try out the original Apple 1 with a 3$ ESP8266 board on your living room TV - wirelessly!
- MOS 6502 CPU emulated at native speed (1 MHz)
- 20 kB RAM
- PAL TV signal output
- Original Signetics 2513 ROM characters
- Telnet used for keyboard input
- Built-in TFTP server for uploading software
- Everything is wireless
The kicker here, though, is that the emulator is completely wireless. You telnet into the 8266 rather than connecting a keyboard directly, and video is transmitted over-the-air using a GPIO pin as a 60-MHz PAL transmitter. A short length of wire is all you need to transmit to an analog PAL TV on channel 4
How does it work?
High frequency modulated video signal is generated internally (via I2S/DMA) and all you need is a single piece of wire to play antenna. Even though it's extremely weak, it can still be picked up on your TV in the same room.
I2S stands for Inter-IC Sound, a standard for digital audio devices interconnect. ESP8266 supports I2S bus data output using DMA transfers, providing a way to generate a steady stream of bits while the processor can do something else. It gets interrupted when the 'bucket' is empty, and it fills it again with more bits to be pumped out.
By generating patterns in those bits, it's possible to produce a meaningful waveform which can be interpreted as a video signal by a TV. Since I live in Europe, the chosen video system is 625 lines CCIR system B (basically PAL B without the color).