Allows you to have two keys instead of one
Allows Arduino micro to control 200 keys instead of 100 = (10*10)
Can easily be modified for standard Arduino and Raspberry Pi
My friend wanted to make a USB keyboard with 112 keys and an Arduino micro and an IO expander (ECE1099).
But neither of us are I2C specialists , therefore I had this idea
Keyboards consist of columns and rows ( see https://docs.qmk.fm/#/hand_wire for deeper explanations )
You sequencialy power ON the columns of your keyboard digitalWrite(colPins[column], HIGH);
then you digitally read the rows digitalRead(rowPins[row]); and the value 0/1 tells you if the key is pressed
My idea is to replace each pushbutton by 2 pushbuttons and 2 resistances
In order to know if a key is pressed you analogically read the rows and with the result you know if 0, 1, or 2 keys are pressed analogRead(rowPins[row]);
Problem we have 1 millisecond delay for stability for each analogRead therefore 100 millisecond (0.1 second) delay for the entire loop
So I made a circuit breadboard to check if the delay was problematic and if my idea was correct
conclusion : it is a success
It is possible to use more than 3 pushbuttons but you may experience voltage problems while reading values due to electromagnetic pollution
final code for the project is here :
https://github.com/fred260571/How-to-build-a-keyboard
bill of material :
resistance 2.1kOhm , 2.7kOhm , 5.6kOhm
diode 1N4005
2 pushbuttons
Because 1 liter of beverage is spoiled on keyboards every year I added 1 diode 1N4005 on each column = digital pin 0, 1, 2, 3, 4, 5, 6, 7, 11, 13
License: GPLv2