A homebrew Apple 1 replica built around the 6502 microprocessor, with a modern microcontroller-based terminal that adds PS/2 keyboard and serial input alongside the original ASCII keyboard interface.
- Overview
- Architecture
- Hardware
- Firmware
- CAD
- Production
- Schematics
- Libraries
- Bill of Materials
- License
The APL1 is a faithful recreation of the 1976 Apple 1 computer, rebuilt as an open-source KiCad project. It preserves the original 6502 + PIA architecture and the classic WozMon firmware experience, while replacing the bulky discrete terminal section of the original with an ATmega1284 microcontroller. The MCU emulates the Apple 1 keyboard and display handshake exactly, but also exposes a PS/2 keyboard port and a serial terminal connection for modern convenience.
- CPU: MOS 6502 running at 1 MHz
- RAM: 32KB SRAM (AS6C62256)
- ROM: 8KB EEPROM (28C64) holding WozMon
- PIA: 65C21 — the Apple 1 keyboard/display interface
- Terminal: ATmega1284(P) controller emulating the original terminal handshake
- Input: Original ASCII keyboard header, PS/2 keyboard, and serial (RS-232) input
- Output: Serial terminal output, with composite video reserved for a future revision
- Bus: 16-bit address bus, 8-bit bidirectional data bus, standard 6502 control signals
- Clock: 1 MHz oscillator for the 6502; 28.63636 MHz crystal (8× NTSC colorburst) for the controller
This repository contains KiCad 7.0+ PCB designs for the APL1 board.
Hardware/APL1/
The single board hosting the 6502 CPU, memory, PIA, and the ATmega1284 terminal controller. Provides:
- CPU: 6502 running at 1 MHz
- RAM: 32KB SRAM (AS6C62256)
- ROM: 8KB EEPROM (28C64) preloaded with WozMon
- PIA: 65C21 keyboard/display interface (original Apple 1 footprint)
- Terminal Controller: ATmega1284(P) running APL1 Controller firmware
- Keyboard buffer: 74LS245 octal bus transceiver
- Glue logic: 74LS04, 74LS00, and 74LS138 address decoder
- Serial: MAX232 level shifter with DB-9 (DTE) connector
- Input: Original ASCII keyboard header and PS/2 keyboard connector
- Video: RCA composite video jack (reserved for a future firmware revision)
- Reset: Keyboard reset and clear controls handled by the controller
- Power: 5V DC via barrel jack, with power switch and indicator LED
Rev 1.1
- Add 10k pull-down resistor
R9for KBDCLR. - Change pull-up resistors
R1-R4from 1k to 4.7k. - Add capacitor
C17for bulk capacitance at power supply.
Rev 1.0
- Initial release.
This repository contains firmware for the terminal controller, the system ROM, and the desktop terminal application.
Firmware/APL1 Controller/
PlatformIO-based firmware for the ATmega1284(P) terminal controller. Provides:
- Faithful emulation of the Apple 1 keyboard and display handshake (DA / RDAB)
- Original ASCII keyboard pass-through via the 74LS245 buffer
- PS/2 keyboard input with a custom Set-2 ISR decoder mapped to Apple 1 ASCII
- Serial (RS-232) terminal input and output at 115200 8N1
- Control shortcuts for clear screen, reset, and throttle ("slow") mode
- Keyboard reset and clear button handling
- Composite video output hooks reserved for a future revision
See Firmware/APL1 Controller/README.md for build, flash, and pin-map details.
Firmware/APL1 ROM/
The system ROM image built from WozMon, Steve Wozniak's original Apple 1 monitor, assembled with the cc65 toolchain and burned to a 28C64 EEPROM.
See Firmware/APL1 ROM/README.md for build and programming instructions.
Firmware/APL1-Terminal/
An Electron + Vue 3 desktop application that provides a faithful CRT terminal experience for the APL1. Connects to the board over the DB-9 serial port at 115200 8N1 and renders output using the original Signetics 2513 character ROM glyphs. Provides:
- 40×24 character canvas rendered with the authentic Signetics 2513 font
- Selectable phosphor color: white, amber, or green
- CRT effects: phosphor glow, scanlines overlay, and screen flicker animation
- Serial port connection and disconnection (auto-detected ports)
- Keyboard input forwarded to the APL1 with Apple 1 control shortcuts (Ctrl+L clear, Ctrl+\ reset, Ctrl+T throttle)
- Built-in program loader with paced character/line sending for 20 bundled Wozmon programs
- Settings panel with per-character and per-line delay controls
- macOS (Apple Silicon DMG), Linux (AppImage / deb), and Windows (NSIS installer) distribution builds, all built locally from macOS
See Firmware/APL1-Terminal/README.md for build and run instructions.
CAD/
3D models and images for the APL1 board and its components.
Production/
JLCPCB-ready fabrication files, BOM, and component positions for PCB fabrication and assembly.
Schematics/
Schematics for the APL1 board.
Libraries/
Shared KiCad symbol and footprint libraries used across the APL1 hardware project.
| Reference | Qty | Value | Description |
|---|---|---|---|
| C1–C10 | 10 | 100nF | Disc Capacitor |
| C11, C14, C15, C16 | 4 | 1µF | Disc Capacitor |
| C12, C13 | 2 | 18pF | Disc Capacitor |
| C31 | 1 | 10uF | Electrolytic Capacitor 16v |
| D1 | 1 | POWER LED | 3.0mm Power LED |
| J2 | 1 | KEYBOARD | ASCII Keyboard Header (DIP-16) |
| J3 | 1 | SERIAL (DTE) | DB-9 Male |
| J4 | 1 | 5V DC | DC Barrel Jack |
| J5 | 1 | PS/2 | 6-pin Mini-DIN (KMDGX-6S-BS) |
| J6 | 1 | VIDEO | RCA Jack (PJRAN1X1U0XX) |
| R1–R4 | 4 | 4.7kΩ | 1/8W Resistor |
| R6 | 1 | 1kΩ | 1/8W Resistor |
| R5 | 1 | 330Ω | 1/8W Resistor |
| R7, R8 | 2 | 820Ω | 1/8W Resistor |
| R9 | 2 | 10kΩ | 1/8W Resistor |
| SW1 | 1 | POWER | SPDT Switch (400MSP1R6BLKM6QE) |
| U1 | 1 | 74LS04 | Hex Inverter |
| U2 | 1 | 6502 | 6502 CPU |
| U3 | 1 | 65C21 | PIA |
| U4 | 1 | AS6C62256 | 32KB SRAM |
| U5 | 1 | 74LS00 | Quad NAND |
| U6 | 1 | 74LS138 | 3-to-8 Decoder |
| U7 | 1 | 28C64 | 8KB EEPROM |
| U8 | 1 | 74LS245 | Octal Bus Transceiver |
| U9 | 1 | MAX232 | RS-232 Transceiver |
| U10 | 1 | ATmega1284-P | Terminal Controller MCU |
| Y1 | 1 | 1MHz | DIP-14 Oscillator |
| Y2 | 1 | 28.636MHz | Crystal |
Hardware designs are released under the CERN Open Hardware Licence Version 2 – Permissive.