3.9 KiB
keybrd Tutorial 4 - Connecting split keyboards
Split keyboards have left and right parts:
- one keyboard half contains the controller and USB port.
- the other keyboard half can contain shift registers or an I/O expander.
The two halves need to be connected. The preferred connection method depends on the number of keys, number of available controller pins, cable flexibility, LEDs, and cost.
Split keyboard connections table
| connection type | controller pins | wire count | max keys |
|---|---|---|---|
| just cable | 3 | 6 | 9 |
| just cable | 3 | 7 | 12 |
| just cable | 4 | 8 | 16 |
| just cable | 4 | 9 | 20 |
| 2 PISO shift registers | 3 | 5 | 16 |
| 3 PISO shift registers | 3 | 5 | 24 |
| I/O expander SPI | 4 | 6 | 64 |
| I/O expander I2C | 2 | 4 | 64 |
Fewer wires makes a cable more flexible. A flexibility cable makes it easy to position the keyboard and route the cable. But if there are enough pins on the controller, using just a cable with more wires is simpler and costs less.
I/O Expanders can power LEDs, while PISO shift registers can not.
I2C is fast enough for scanning up to 5 rows. SPI is much faster, but requires 2 additional wires.
More scanning options are reviewed at http://www.openmusiclabs.com/learning/digital/input-matrix-scanning/
Cables table
| connector name | wire count |
|---|---|
| TRRS | 4 |
| 6-pin mini-DIN connector (PS/2) | 4 |
| USB 2 | 4 |
| 4P4C Modular connector (RJ9, RJ10, RJ22) handset plug | 4 |
| 6P4C Modular connector (RJ-14) 2-line phone | 4 |
| 6P6C Modular connector (RJ12) 3-line phone | 6 |
| eSATA | 7 |
| 8p8c Modular connector (RJ45) Ethernet | 8 |
| USB 3.0, 3.1 | 9 |
Only ready-made cables that are widely available are listed. There are hundreds of other connectors listed at http://pinouts.ru/ There are also wireless options at the expense of adding complexity and maintaining a battery.
The 8-wire "GearIT Cat 6 Ethernet Flat Patch Cable 7 Feet" is very flexible. It's available at Walmart (9/19/16) if you want to feel the merchandise before you buy. All the modular connector cables are available in the flat form factor.
For prototyping on perfboards, consider a 0.1" header.
keybrd tutorial by Wolfram Volpi is licensed under a Creative Commons Attribution 4.0 International License.
Permissions beyond the scope of this license may be available at https://github.com/wolfv6/keybrd/issues/new.