Custom keyboards from the matrix up lesson plan
Scan a key matrix, see ghosting and the diode that stops it, then add layers, a knob and per-key light.
Objectives and materials
By the end, students can
- Rows, columns, the scan, and why every key gets a diode.
- A layered keymap, an encoder and one LED per key.
Materials for the whole unit
- Addressable RGB LEDs
- Diode x 12
- Full-size breadboard
- Half breadboard x 4
- Keypad, 4x4
- Pushbutton x 12
- Rotary encoder, KY-040
- SparkFun Pro Micro
Every part is already on the simulator’s bench, so there is nothing to buy or hand out. The counts are the most any one lesson uses, if you build it on real breadboards too.
The matrix
Rows, columns, the scan, and why every key gets a diode.
| Lesson | Time | What students do |
|---|---|---|
| Rows, columns and the scanWhy twelve keys need only seven pins: drive one row LOW at a time, read the columns, and find every key by its row and column. | 55 min |
|
| Ghosting, and why every key gets a diodeScan a membrane keypad that has no diodes, hold three keys on a rectangle and watch a fourth appear, then see how one diode per key stops it. | 55 min |
|
Materials
- Addressable RGB LEDs
- Diode x 12
- Full-size breadboard
- Half breadboard x 4
- Keypad, 4x4
- Pushbutton x 12
- Rotary encoder, KY-040
- SparkFun Pro Micro
Check for understanding
Each student finishes "Ghosting, and why every key gets a diode" on their own, without opening the hints. The simulator checks 5 of its 5 steps as they go.
Then ask each one to explain, in a sentence or two, the last thing it asked of them: "One diode per key".
The keyboard
A layered keymap, an encoder and one LED per key.
| Lesson | Time | What students do |
|---|---|---|
| Layers, a knob and per-key lightTurn the matrix into a keyboard: a keymap with layers you hold and toggle, an encoder that scrolls or steps by layer, and one WS2812B per key. | 70 min |
|
Materials
- Addressable RGB LEDs
- Diode x 12
- Half breadboard x 4
- Pushbutton x 12
- Rotary encoder, KY-040
- SparkFun Pro Micro
Check for understanding
Each student finishes "Layers, a knob and per-key light" on their own, without opening the hints. The simulator checks 6 of its 6 steps as they go.
Then ask each one to explain, in a sentence or two, the last thing it asked of them: "From here to QMK or KMK".
Teach this unit as a class
Start a class from this course and its 3 lessons are assigned in one go, in order. Students join with a six-character code or printed login cards, and each one’s work comes back to you.
The class tools are free for 30 days for one class of up to 20 students, with no card. The lessons themselves are free either way.