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 if you don't mind 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.
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keybrd tutorial by Wolfram Volpi is licensed under a Creative Commons Attribution 4.0 International License.
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