Teaching with Keyboard Builder

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Keyboard Builder is one keyboard on five benches: Build, Switch, Matrix, Keymap and Type. What a student picks on one bench is the board on all of them. Twelve orders from customers are the puzzles. An order closes when the keyboard passes its test, and the test reads the keyboard as built, so a student cannot close an order by clicking around.

Students arrive knowing the videos: the sizes, the switch colors, the sound. That is the way in, and the Build bench gives it to them. The teaching is on the other four benches. If time is short, do the Matrix bench and skip the rest.

The app opens on a plain 60 percent board. Key sounds are off until a student turns them on, and Setup can keep them off for the whole class.

Three periods

Period 1, the Matrix bench: how a keyboard finds a key.

1. Count the pins (5 minutes) On the projector, ask how many wires a keyboard with 61 keys needs. Open the Matrix bench and pick Wiring: One wire per key. The chip reads 61 pins and the line says the controller has 26. Pick Rows and columns: 19 pins. Ask what was given up to get from 61 to 19. Nobody will know yet.
2. Watch the scan (5 minutes) Click one key so it stays down. A bright pulse steps along the columns, and the key lights when the pulse reaches its column. Press Step one column to move it by hand. A small controller does this whole pass about 1,800 times a second.
3. Catch the ghost (10 minutes) Students take the order A letter nobody pressed and click Q, W and A so all three stay down. Within a few seconds S lights pink, and the line reads: The board sees 4 keys. You are holding 3. Ask what the four keys have in common. They are the corners of a rectangle: two rows, two columns. That is what the 19 pins cost.
4. Fix it two ways (15 minutes) Turn Diodes on and hold the same three keys: three lights, and the order closes. Then take It says anti-ghosting on the box: diodes off, Block the doubt, the same three keys. No ghost, and the line says the board dropped A. Students pick what anti-ghosting meant on that board.
5. Their own keyboards (10 minutes) Students click the board, then hold Q, W and A on the real keyboard in front of them and read the count under The keyboard in front of you. If it stops at 2, their keyboard dropped the third key. Have them hunt for other threes that fail. Which ones fail depends on the keyboard, so there is no answer key for this part.

Period 2, the Keymap and Type benches: what a key sends.

1. A key sends a number (10 minutes) On the Type bench students click the keyboard and type. The line under it reads, for example: Row 2, column 9. The board sent code 0C. Your computer turned that into "i". Hold Shift and press a letter: the line says Shift turns on one of eight modifier bits, and the letter's code does not change. Ask who makes the capital.
2. Arrows on a board with none (15 minutes) Students take Arrows under my fingers. On the Keymap bench they pick Layer 1, click I and pick the up arrow, and do the same for J, K and L. The order closes. On the Type bench they click Fn on the board, which holds it down, and press I: the line says Layer 1 answered and the code is 52. A Chromebook or a Mac has no key where this board has Fn, which is why a click holds it.
3. Backspace on Caps Lock (5 minutes) Nobody needs Caps Lock there. The catch is in the customer's second sentence: Caps Lock has to go somewhere. A student who only does the first half is told they now have no Caps Lock at all.
4. One key, a whole line (10 minutes) One key for a whole line: a macro that types Thanks, Sam, on a key. The line under the Type bench says the board pressed 13 keys, Shift included. Ask where the other two came from.
5. Does Fn reach the computer? (5 minutes) Ask the class. On a board like this one it never does: the keyboard's own controller reads Fn and only changes which layer it looks at.

Period 3, the Switch bench, repairs and the build sheet.

1. Press it slowly (10 minutes) On the Switch bench pick Light linear and press Press it slowly. The dot climbs a straight line, the key is sent at 2 mm with 45 grams of push, and the bottom is at 4 mm. Pick Tactile: the dot goes over a hill of 55 grams at 1.3 mm, before the key is sent. Ask where on the graph the key is sent. It is never the bottom.
2. Where is the click? (5 minutes) With sound on, press Clicky slowly. The click comes partway down, before the key is sent. Sharp clicky clicks right about where the key is sent and again, more quietly, on the way up.
3. A dead key (10 minutes) My H does nothing. Students click keys on the Matrix bench until they find the one that is outlined and never lights, then choose a repair for that key: its switch, its column line or its row line. A wrong choice is counted and the customer says why it was wrong.
4. A dead column (10 minutes) A column of keys died at once. The reasoning is the lesson: several keys dying together points at what they share. One switch cannot stop a whole column.
5. The build sheet (10 minutes) Build sheet in the top bar: the keyboard's picture, its parts and price, what the student changed, the orders closed, and the written questions. Hand in needs an answer to every question.

What students get wrong, and where the app answers it

These are beliefs teachers report. We found no study of how students think a key press reaches the screen, so treat the left column as things to listen for, not as measured.

The twelve orders

An order closes only while it is the one in hand, so a board that happens to fit another customer does not close an order nobody read. A failed test answers the way the customer would, one thing at a time.

The budgets are tight on purpose. The school store order can only be met by keeping the case, plate and caps at their cheapest.

What the app simplifies, on purpose

• The matrix is the textbook circuit. A real board also depends on resistance, and real boards sometimes fold the rows and columns another way to save pins. A full-size board laid out plainly needs 27 pins, one more than a small controller has, and the app says so.
• The ghost key is on the simulated board only. A laptop keyboard never shows one: it drops the doubtful key.
• The switch numbers are real: Cherry's pages for five switches and sellers' listings for the sixth. The line between those numbers on the graph is drawn to match one measured switch of each kind. Two switches of the same kind differ.
• On the real clicky switch with a collar, the leg that works the metal leaves is part of the collar. The cutaway draws it on the stem.
• Contact bounce on the high school level is a made-up typical pattern. A real one is different on every press.
• The sounds are made by the app. What the case, the plate, the mount, the foam and the cap plastic do to the sound follows what builders say. Nobody has published measurements, and every such line in the app starts with Builders say.
• Prices are round numbers typical of 2026.
• Filling the report with 01 on a seventh key is what the USB rule asks for. Many real boards just leave the seventh key out.
• Fn is never sent on a board like this one. Some keyboards do report it.
• Left out altogether: soldering, lubing, lights, wireless, layouts from other countries, split and grid boards, and writing real firmware.

An independent review checked every key code, datasheet number, help sentence and answer key against sources before the app went live. What it found wrong was fixed, and what is still a judgment is in the list above.

Middle school and high school

The level is a menu in the top bar. Middle school, the default, uses plain words: rows, columns, pins, ghost key, layer, a key's code as a number, grams and millimeters.

High school adds three things. On the Type bench, the eight-byte report being sent: the modifier bits, a byte that is always 00, then up to six keys, and what a seventh key does to it. On the Switch bench, the dashed return line, which sits lower because of rubbing, and the clicky collar switch letting go a little higher than it catches. And contact bounce: with the controller waiting 0 ms, one press is counted four times; waiting 5 ms, once.

The build sheet, Setup and the answer key

The build sheet has the keyboard's picture, its parts and price, the matrix numbers, the keys the student changed, the orders closed, and ten written questions: pins, the ghost, the two fixes, what dead keys share, where a key is sent on the force graph, what Shift and A sends, layers, Fn, whether a switch makes you faster, and one build order. Hand in needs every answer, and editing an answer after handing in takes the sheet back. Print gives the sheet alone, two pages.

Setup, in the top bar, is for the teacher. It picks which of the ten questions are on the sheet, adds up to ten of your own, and opens the answer key. It also has two switches for the room: keep the key sounds off for the class, and leave out the timed line on the Type bench.

The choices are saved in the project. Set it up, save, and share the project with the class as a starter.

The timed line and the sounds

The Type bench has a short line to type. The clock starts on the first key and stops at the end of the line or after a minute. A wrong key does not move the line on. The result is words a minute, counting five keys as a word, percent right, and the keys missed most. It is never saved, never on the share page, and there is no leaderboard. If speed makes your class anxious, leave it out in Setup.

Thirty keyboards clicking is a lot. Sound is off until a student turns it on. Headphones solve it, and so does the switch in Setup. A student who cannot hear loses nothing that an order or the sheet depends on.

The sound tuner on the Type bench has five sliders (pitch, ring, brightness, the sound coming back up, and the click) and four starting points in the builders' own words: thocky, clacky, creamy and poppy. It changes the sound the app makes. It is there because the sound is why students care, and it is not a claim about what any real part does.

Standards

• CSTA 2017, grades 9 and 10. 3A-CS-01: explain how abstractions hide the underlying implementation details of computing systems embedded in everyday objects. 3A-CS-02: compare levels of abstraction and interactions between application software, system software and hardware layers.
• CSTA 2017, grades 6 to 8. 2-CS-03: systematically identify and fix problems with computing devices and their components (the repair orders). 2-CS-01: recommend improvements to the design of computing devices, based on an analysis of how users interact with the devices (the build orders, when students argue their choice for the customer).
• CSTA 2017, grades 3 to 5, for a younger group. 1B-CS-02: model how computer hardware and software work together as a system to accomplish tasks.
• CSTA 2026. HS-SYS-HW-30: demonstrate the capabilities and limitations of a physical or simulated computing device to address a task or problem.
• ITEEA STEL-2M: differentiate between inputs, processes, outputs and feedback in technological systems.
• CompTIA Tech+ (FC0-U71): 1.4, explain the troubleshooting methodology, and 2.4, install and configure common peripheral devices.

Not claimed: keyboarding standards such as CCSS W.6.6, because the app does not teach typing, and NGSS MS-PS4-3, whose boundary leaves out the specific mechanism of any given device.

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