tutorial-1b.md

Tutorial: Butty the single-button keyboard (part 2)

This article continues from part 1 and discusses walls.

At the end of part 1, Butty was a mounting plate for a switch, and nothing more. We want more support: Enough material around the plate to have it stand on a desk, with a switch in it, without falling over.

A bevel around the mounting plate

We will begin with a point of aesthetics. Rather than adding a wall straight down from the edges of the plate to the floor, we’ll add a bevel around the plate. Change butty.yaml to contain this:

key-clusters:
  main:
    anchoring:
      extrinsic-offset: [0, 0, 10]
by-key:
  parameters:
    wall:
      extent: 1

Default extent is 0. The parameter is documented here.

The command to run the application is, and will continue to be:

# lein run -c config/base.yaml -c butty.yaml

Here’s body-main.scad with the new configuration:

A bevel has appeared, lining the edge of the keyboard. Here’s how it works:

The keyboard case extends from each key mount. At the edge of a key cluster—as on every side of Butty—there is a wall. This wall was at extent 0, meaning the edge of the mounting plate, so we couldn’t see it.

Walls are built one segment at a time. Segments are points in space around the key mount. Segment 0 is a corner of the plate itself. The position of segment 1, relative to segment 0, is determined for us in base.yaml, the bundled base configuration file. Here’s an excerpt from base.yaml:

    wall:
      segments:
        "1":
          intrinsic-offset: [0,  1, -1]  # Top bevel.

This setting means that segment 1 is 1 mm out from each corner of Butty, and 1 mm down. By connecting each corner with a point off that corner at those coordinates, in a rotating frame of reference specific to each side, we get a bevel all the way round.

Bringing the wall to the ground

Change butty.yaml to have the following contents, and run the application again.

key-clusters:
  main:
    anchoring:
      extrinsic-offset: [0, 0, 10]
by-key:
  parameters:
    wall:
      extent: 1
      to-ground: true  # New line!

⤤ The wall of the keyboard case now extends vertically from the segment specified by our setting for extent all the way to the ground at z-coordinate 0. The total height of the case is 10 mm, given by our extrinsic-offset.

You see there is still room inside the case for a key switch. You could print this version of Butty, mount a switch in it, and click away to your heart’s content.

An opening to the north

Butty is a single-button keyboard, but even a single-button keyboard needs more parts than just a button. In order to send signals to a computer, Butty needs a microcontroller. We will be adding one of those in part 3. For now, we’ll prepare by opening up a hole in the wall on Butty’s back side.

We do this by specifying exceptions to the settings we have already made.

key-clusters:
  main:
    anchoring:
      extrinsic-offset: [0, 0, 10]
by-key:
  parameters:
    wall:
      extent: 1
      to-ground: true
  sides:
    NNE:
      parameters:
        wall:
          extent: 0
          to-ground: false
    NNW:
      parameters:
        wall:
          extent: 0
          to-ground: false

In this version of butty.yaml, the by-key section has both parameters for the whole keyboard and two other sets of parameters: One for each corner at Butty’s back.

The wall we have seen so far is drawn between eight sides of Butty, designated by eight intermediate points of the compass. By providing exceptions for the “north by northeast” and “north by northwest” sides, restoring default settings for those sides alone, we break the wall where we want to. The metaphor of the compass is explained here.

It’s a clean cut. Here’s another angle:

Summary

In this part of the tutorial, we have learned:

• How to make walls with extent and to-ground.
• How to target the sides of a key: Using the names of compass points.
• How to make exceptions.

In part 3, we’ll add a microcontroller.