59 lines
3.7 KiB
Markdown
59 lines
3.7 KiB
Markdown
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keybrd Tutorial 4a - Connecting split keyboards
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===============================================
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Split keyboards have left and right parts:
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* one keyboard half contains the controller and USB port.
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* the other keyboard half can contain shift registers or an I/O expander.
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The two halves need to be connected.
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The preferred connection method depends on the number of keys, number of available controller pins, cable flexibility, LEDs, and cost.
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## Split keyboard connections table
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| connection type | controller pins | wire count | max keys |
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|:----------------------:|:---------------:|:----------:|:--------:|
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| just cable | 6 | 6 | 9 |
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| just cable | 7 | 7 | 12 |
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| just cable | 8 | 8 | 16 |
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| just cable | 9 | 9 | 20 |
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| | | | |
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| 2 PISO shift registers | 3 | 5 | 16 |
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| 3 PISO shift registers | 3 | 5 | 24 |
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| | | | |
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| I/O expander SPI | 4 | 6 | 64 |
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| I/O expander I2C | 2 | 4 | 64 |
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Fewer wires makes a cable more flexible.
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A flexibility cable makes it easy to position the keyboard and route the cable.
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But if there are enough pins on the controller, just using a cable with more wires is simpler and costs less.
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I/O Expanders can power LEDs, while PISO shift registers can not.
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I2C is a little slow if the I/O expander is scanning more than 4 rows.
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## Cables table
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| connector name | wire count |
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|:-----------------------------------------------------:|:----------:|
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| TRRS | 4 |
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| 6-pin mini-DIN connector (PS/2) | 4 |
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| USB 2 | 4 |
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| 4P4C Modular connector (RJ9, RJ10, RJ22) handset plug | 4 |
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| 6P4C Modular connector (RJ-14) 2-line phone | 4 |
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| 6P6C Modular connector (RJ12) 3-line phone | 6 |
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| eSATA | 7 |
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| 8p8c Modular connector (RJ45) Ethernet | 8 |
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| USB 3.0, 3.1 | 9 |
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Only ready-made cables that are widely available are listed.
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There are hundreds of other connectors listed at http://pinouts.ru/
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There are also wireless options if you don't mind adding complexity and maintaining a battery.
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The 8-wire "GearIT Cat 6 Ethernet Flat Patch Cable 7 Feet" is very flexible.
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It's available at Walmart if you want to feel the merchandise before you buy.
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All the modular connectors are flat.
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For prototyping on perfboards, consider a 0.1” header.
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<br>
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<a rel="license" href="https://creativecommons.org/licenses/by/4.0/"><img alt="Creative Commons License" style="border-width:0" src="https://licensebuttons.net/l/by/4.0/88x31.png" /></a><br /><span xmlns:dct="http://purl.org/dc/terms/" property="dct:title">keybrd tutorial</span> by <a xmlns:cc="https://creativecommons.org/ns" href="https://github.com/wolfv6/keybrd" property="cc:attributionName" rel="cc:attributionURL">Wolfram Volpi</a> is licensed under a <a rel="license" href="https://creativecommons.org/licenses/by/4.0/">Creative Commons Attribution 4.0 International License</a>.<br />Permissions beyond the scope of this license may be available at <a xmlns:cc="https://creativecommons.org/ns" href="https://github.com/wolfv6/keybrd/issues/new" rel="cc:morePermissions">https://github.com/wolfv6/keybrd/issues/new</a>.
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