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 peripheral hand.

Overview of split keyboard with shift registers

Only the right matrix is shown. The left matrix was omitted to reduce clutter.

The layout has 2 rows and 7 columns. Electronically, the matrix only has one row. Diodes are not needed because there is only one row.

The two black rectangles are shift registers daisy chained together. Shift register details are in the SN74HC165N datasheet.

Building a split breadboard keyboard with shift registers

Add components to the breadboard as shown in the picture.

Each shift register has a small notch on one end to identify pin 1. In the picture, pin 1s are on the left 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. There are 14 keys, so 2 of the input pins are unused. Used input pins are connected to 10k pull-down resistor which are grounded (blue bus). Unused input pins are grounded (blue bus).

A decoupling capacitor between the power and ground wires prevents power disturbance.

Switches are connected to power (red bus) and shift register input pins (jumpers).

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

74HC165 left (lower half of breadboard)
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                         blue bus
 D5     4    parallel input                         blue bus
 D6     5    parallel input                         blue bus
 D7     6    parallel input                         blue bus
/QH     7    ~serial output
GND     8    ground              gnd                blue bus

74HC165 right (upper half of breadboard)
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                         blue bus
 D2     13   parallel input                         blue bus
 D1     12   parallel input                         blue bus
 D0     11   parallel input                         blue bus
SER     10   serial input                           blue wire to next QH
 QH      9   serial output       MISO0 12           blue wire to previous SER

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.

The sketch has code for both left and right matrix. Notice that the left matrix is active low, while the right matrix is active high.

Exercises

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

2. Add a left matrix to Teensy. There is room between Teensy and the shift registers for a 1-column matrix. The bus strips are occupied by the right keys, so use terminal strips instead. Other wise it is similar to the 2-column matrix in tutorial_1_breadboard_keyboard.md.

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.

parts for breadboard_keyboard_supplies.ods