KC8A Programmer's Panel

A colleague of mine bought a PDP-8/A, and didn't have a programmer's panel for it. The front panel on the 8/A comes in two parts. All of them have a "Limited Function" panel, which has a couple of switches for power and bootstrap. The "Programmer's Panel" adds a keypad and an 7-segment LED octal display. Programmer's panels appear from time to time on eBay, but rather than wait for one to appear, we decided to build one.

Working from DEC's drawings, he and I drew up a pair of PCB's in Eagle to mimic the originals from DEC. As always, issues of authenticity will come up, and since nothing like the original keypads seemed to be available, we used a bunch of fairly ordinary tactile switches and their optional key-caps.

Here are some photos of the boards as they came back from the fab:

KC8A boards as they came from the fab.

KC8A boards after a trip through the band-saw to separate them.

The original panels are constructed on a pair of PCB's, mounted with spacers, and their solder sides facing each other. Our replacement follows the original as closely as we could, and here are some pictures of the assembled sandwich:

The boards mount back to back.

Here's the side that faces out.

Here's the side that faces inward, toward the backplane.

That's as far as I took mine, since I have an original programmer's panel, but the other prototype did get debugged. There were some blue wires needed. The original DEC drawings have nomenclature differences between the drawings for the two boards! As a consequence, a few signals got connected wrong in the PCB. Also, the PCB has a totally inadequate ground plane (as does the original DEC design). So his prototype also has some extra ground wires running around the board in a grid design. If I were to make more of these, I'd do a polygon fill for the ground plane, and fix up those blue wire problems in the etch.

There was also a panel design using FrontPanel Express' software, and a bunch of time and effort was spent being as sure as possible that the PCB's parts placement would line up with the front panel artwork, and actually fit in the PDP-8/A properly. Here are some pictures of my fiddling with mock-ups:

An exterior view of the mockup.

Here's the inside, with the "boards" attached.

Checking the fit on the right.

Checking the fit on the left.

Last updated on 02/25/23 02:20