keybrd Tutorial 4b - split keyboard with shift registers

When you finish this tutorial you will be able to be able to modify a 2-matrix keybrd sketch to suite your own split keyboard design.

Overview of split keyboard with shift registers

The breadboard in the following picture models a split keyboard.

The primary matrix on the left has one column, which is read by a microcontroller pin. The secondary matrix on the right has 4 columns, which are read by the shift register input pins. The primary and secondary matrices share the same rows, which are strobed by micro-controller pins. Both matrices are active low.

Building a split keyboard with shift registers

The breadboard keyboard modifies the basic breadboard keyboard described in tutorial_1_breadboard_keyboard.md

Add components to the breadboard as shown in the picture.

The shift register is a SN74HC165N. Details are in the SN74HC165N datasheet.

Each shift register has a small notch on one end to identify pin 1. In the picture, 1 pins are on the right end. Shift registers are chained together by colored wires that lay flat on the breadboard.

Each shift register has 8 parallel input pins, 4 on each side. The breadboard doesn’t have enough room for 16 columns; only 4 columns are connected to the shift registers. Every 4th input pin is connected to a matrix column and a pull-up resistor. Unused input pins are connected to power. The red bus strips power the pull up resistors and unused input pins.

A decoupling capacitor between the power and ground wires dampens noise coming in through those wires.

Blue bus strips are used for strobing rows

I apologize for not having a schematic. This table should help you figure out the pictures:

74HC165 left (upper half of breadboard)
NAME    PIN# I/O DESCRIPTION         DESTINATION     PIN#   CHAIN (wires flat on breadboard)
SH/LD   1    I   shift or load input Teensy LC CS0   10     red wire
CLK     2    I   clock input         Teensy LC SCK0  13     green wire
 D4     3    I   parallel input      pull-up resistor       red bus
 D5     4    I   parallel input      power                  red bus
 D6     5    I   parallel input      power                  red bus
 D7     6    I   parallel input      power                  red bus
/QH     7    O   ~serial output      Teensy LC MISO0 12
GND     8        ground              gnd                    black wire

74HC165 right (lower half of breadboard)
NAME    PIN# I/O DESCRIPTION         DESTINATION            CHAIN (wires flat on breadboard)
VCC     16       power pin           Teensy LC 3.3V         red bus
CLK INH 15   I   clock inhibit       gnd                    black wire
 D3     14   I   parallel input      power                  red bus
 D2     13   I   parallel input      power                  red bus
 D1     12   I   parallel input      power                  red bus
 D0     11   I   parallel input      pull-up resistor       red bus
SER     10   I   serial input        next QH                yellow wire
 QH      9   O   serial output       previous SER           yellow wire

Sketch for split keyboard with shift registers

keybrd_4b_split_keyboard_with_shift_registers.ino is a simple sketch with two shift registers. The sketch will run on the above breadboard keyboard. Annotations in the sketch explain the code.

Exercises

1. Guess what happens if an unused input pin is not powered? Try it.

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.