Keypad problems.

Projects General Guidance
1

I'm using a 4x4 keypad from Jameco (this one) for user input with an Arduino Mega. The problem is, reading it doesn't work much at all.

#include <Wire.h> 
#include <LiquidCrystal_I2C.h>



#define I2C_ADDR      0x3F
#define BACKLIGHT_PIN 3
#define En_pin        2
#define Rw_pin        1
#define Rs_pin        0
#define D4_pin        4
#define D5_pin        5
#define D6_pin        6
#define D7_pin        7

#define KPC1          22
#define KPC2          24
#define KPC3          26
#define KPC4          28
#define KPR1          30
#define KPR2          32
#define KPR3          34
#define KPR4          36

LiquidCrystal_I2C lcd(I2C_ADDR,En_pin,Rw_pin,Rs_pin,D4_pin,D5_pin,D6_pin,D7_pin, BACKLIGHT_PIN, POSITIVE);

int pl=0;
void setup()
{
  
  lcd.begin(20,4);
  Serial.begin(9600);
  lcd.print("start");
  delay(1000);
  lcd.clear();
  lcd.home();
  pinMode(KPR1,OUTPUT);
  pinMode(KPR2,OUTPUT);
  pinMode(KPR3,OUTPUT);
  pinMode(KPR4,OUTPUT);
  pinMode(KPC1,INPUT_PULLUP);
  pinMode(KPC2,INPUT_PULLUP);
  pinMode(KPC3,INPUT_PULLUP);
  pinMode(KPC4,INPUT_PULLUP);
  for(int i=22;i<=36;i+=2){digitalWrite(i,LOW);}
}

void loop()
{
  digitalWrite(KPR1,HIGH);
  delay(2);
  if(!digitalRead(KPC2)){if(pl!=1){lcd.print("!");pl=1;}Serial.println("!");}else{pl=0;lcd.clear();}
  digitalWrite(KPR1,LOW);
  delay(2);
}

Currently, my code (should) only read the first row, second column, so:

[ ][ ][ ][ ]
[ ][ ][ ][ ]
[ ][ ][ ][ ]
[ ][x][ ][ ]

Pressing the button that I'm trying to read will affect the output, but so do many of the other buttons, and some of them seem to latch it. Any ideas?

2

Hi,

Your setup() is performing digitalWrite(LOW) on the pins that just got set to INPUT_PULLUP. This will switch off the internal pullups.

I would suggest trying this: set all your row pins to input without pullup in setup(). Then, in loop(), switch one row at a time to output and low, read the columns and then set the row back to input.

Paul

3

I tried your idea, but it seems that no matter how I read the inputs and set the outputs, I have the same problem.
It seems that whatever button I try to read acts like this: It, and all the buttons lower in its column, trigger a button press. All the buttons higher in its column, as well as the two to the left and right of the one above it, seem to latch it so that a button press is always reported.

Where L is latching, T is target, and P is reporting press:
[ ][ ][L][ ]
[ ][L][L][L]
[ ][ ][T][ ]
[ ][ ][P][ ]

On the edges and corners the same rules mostly hold true, but with more weirdness.

To me it seems like this would just be a broken keypad, but here's something else that didn't occur to me earlier:
For cable management purposes, all 8 wires from the keypad to the Arduino are twisted together in a bundle. Is there any chance that there could be interference between the wires?

4

Why are you not using the keypad library? It does everything your doing and more.

5

I am now, it works great. Thanks!
Also, I might have had a problem due to plugging all my wires in 1 hole to left on the Arduino headers, leaving one of the columns connected to ground...