Land Boards Launches I2C Push-Button Front Panel for Your Next Retro-Computing Project
Classic bit-by-bit program entry now available to those whose budget doesn't stretch to a panel full of classic rocker switchers.
Land Boards' Doug Gilliland has released a front-panel design for selected vintage microprocessors, meant to offer the same functionality as a classic rocker-switch panel but with cheaper push-button switches and single-color LED status lights.
In the very earliest days of computing, an electronic computer was programmed by the physical moving of patch cables between sockets. Later came the punch-cards and paper tapes, carrying encoded information in the form of holes arranged in a particular way; still later magnetic media allowed users to load programs from tape cassettes or floppy disks. For those who cut their teeth on early microcomputers like the venerable Altair 8800, though, there was really only one option: loading a program by the laborious toggling of individual bits of memory using toggle switches on the front panel.
The first upgrade for most microcomputer owners was some form of storage device, even if just a punch-tape reader. The loader still needed to be entered by hand, though, and there are those building modern incarnations of classic machines who still like to feel the program going in bit-by-bit — and it's for these Gilliland has designed the a simple front-panel PCB.
"I wanted a front panel but with a future twist," Gilliland explains of the reason for his design. "Most front panels have rocker switches which are really expensive. But push-button switches should be able to do the same thing, right? Yes, they can! I am using it as the Front Panel for a Z80 retro-computer project but it could be used with any 8-bit CPU which has an I2C interface (or can emulate one in software)."
The design is simple: 32 push-button switches and 32 single-color status LEDs are connected to four MCP23017 16-bit I2C port expanders, then the front-panel board connects to the host system over the I2C bus. For projects which use I2C for communication with more hardware, the addresses used are configurable and a daisy-chain connector is included to make adding more devices as simple as possible.
Gilliland is selling the bare PCBs through Tindie for $10 plus shipping, while the source files are available on his GitHub repository. Additional documentation is available on the Land Boards website.