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- keybrd Tutorial 4b - split keyboard with shift registers
- ========================================================
- When you finish this tutorial you will be able to be able to modify a split keybrd sketch with 10 to 24 keys on the shift registers.
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- Overview of split keyboard with shift registers
- -----------------------------------------------
- The breadboard in the following picture models a split keyboard.
- The green rectangle on the left is a Teensy LC micro controller.
- The black rectangles in the middle are two SN74HC165N shift registers daisy chained together.
- The micro controller and shift registers are connected via 5 jumper wires.
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- Only the right matrix is shown. The left matrix is not needed for this demonstration and was omitted to reduce clutter.
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- The right-matrix layout has 2 rows and 7 columns.
- Electronically, there is only one row of keys.
- Diodes are not needed because there is only one row.
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- 
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- Building a split breadboard keyboard with shift registers
- ---------------------------------------------------------
- Add components to the breadboard as shown in the picture.
- Refer to the SN74HC165N datasheet to locate its pins.
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- In the picture, SN74HC165N pin 1s are on the left end, towards the controller.
- Shift registers are chained together by colored wires that lay flat on the breadboard.
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- Each shift register has 8 parallel input pins, 4 on each side.
- 14 input pins and their keys are connected to 10k pull-down resistor which are grounded (blue bus).
- 2 input pins are not used, they are grounded (blue bus).
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- Switches are connected to power (red bus) and shift register input pins (jumpers).
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- This table lists what gets connected to the 74HC165 pins:
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- **74HC165 left (lower half of breadboard)**
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- |NAME |PIN#|DESCRIPTION |TO TEENSY LC PIN#|CHAIN |
- |:-------|:--:|:-------------------|:----------------|:----------|
- |SH/LD |1 |shift or load input |CS0 10 |green wire |
- |CLK |2 |clock input |SCK0 13 |yellow wire|
- | D4 |3 |parallel input | | |
- | D5 |4 |parallel input | | |
- | D6 |5 |parallel input | | |
- | D7 |6 |parallel input | | |
- |/QH |7 |~serial output | | |
- |GND |8 |ground |gnd |blue bus |
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- **74HC165 right (upper half of breadboard)**
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- |NAME |PIN#|DESCRIPTION |TO TEENSY LC PIN#|CHAIN |
- |:-------|:--:|:-------------------|:----------------|:------------------------|
- |VCC |16 |power pin |3.3V |red wire |
- |CLK INH |15 |clock inhibit | |blue bus |
- | D3 |14 |parallel input | | |
- | D2 |13 |parallel input | | |
- | D1 |12 |parallel input | | |
- | D0 |11 |parallel input | | |
- |SER |10 |serial input | |blue wire to next QH |
- | QH | 9 |serial output |MISO0 12 |blue wire to previous SER|
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- 
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- 
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- A decoupling capacitor between the power and ground wires suppresses noise.
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- I apologize for not providing a schematic.
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- Sketch for split keyboard with shift registers
- ----------------------------------------------
- [keybrd_4b_split_keyboard_with_shift_registers.ino](keybrd_4b_split_keyboard_with_shift_registers/keybrd_4b_split_keyboard_with_shift_registers.ino) is a simple sketch with two shift registers.
- It will run on the above breadboard keyboard.
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- Exercises
- ---------
- 1. Guess what happens if an unused input pin is not grounded? Try it.
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- <br>
- <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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