Technique to use a matrix keypad from GPIO

[aduroch]

Hello,
I'm having a hardtime configuring an hardware matrix keypad 4x4 within Node Red, using GPIO on a raspberry PI 3B+ All the hardware is set and works good. I use Gpio Input pull-down for rows and Gpio Output for Columns, initial level high, but I need some logic to use it in Red Node. I just want to press on digit on the keypad and get a payload of that digit in a debug node to start. A working solution example would be great. I tried join payload to create a binary string that I can compare to a known value but it always finish with a lot of complexity and it is not so much reactive.
Thanks.

[cymplecy]

I'm thinking that if I wanted to do this, I'd write a little python program to do the actual matrix polling (should be examples of that out there) and then launch it via exec node and monitor it's output

[aduroch]

I've never used anything outside node red using simple node for programming but I'll have a look on your suggestion. If I remembered, I saw something programmed with an array and interfacing directly with gpio, using terminal console but I don't know if it was programmed in Python, which I don't know nothing about but I'm very open to put my hands on it. Thanks!

[aduroch]

It works in mimutes, thanks a lot my friend!

[cymplecy]

I thought that would be the way to do it

And very impressive that you got it working so quickly

Can you post the python code here just in case someone needs it in future?

[aduroch]

# This example is a hello world example
# for using a keypad with the Raspberry Pi

import RPi.GPIO as GPIO
import time

L1 = 5
L2 = 6
L3 = 13
L4 = 26

C1 = 23
C2 = 24
C3 = 25
C4 = 12

GPIO.setwarnings(False)
GPIO.setmode(GPIO.BCM)

GPIO.setup(L1, GPIO.OUT)
GPIO.setup(L2, GPIO.OUT)
GPIO.setup(L3, GPIO.OUT)
GPIO.setup(L4, GPIO.OUT)

GPIO.setup(C1, GPIO.IN, pull_up_down=GPIO.PUD_DOWN)
GPIO.setup(C2, GPIO.IN, pull_up_down=GPIO.PUD_DOWN)
GPIO.setup(C3, GPIO.IN, pull_up_down=GPIO.PUD_DOWN)
GPIO.setup(C4, GPIO.IN, pull_up_down=GPIO.PUD_DOWN)

def readLine(line, characters):
    GPIO.output(line, GPIO.HIGH)
    if(GPIO.input(C1) == 1):
        print(characters[0])
    if(GPIO.input(C2) == 1):
        print(characters[1])
    if(GPIO.input(C3) == 1):
        print(characters[2])
    if(GPIO.input(C4) == 1):
        print(characters[3])
    GPIO.output(line, GPIO.LOW)

try:
    while True:
        readLine(L1, ["1","2","3","A"])
        readLine(L2, ["4","5","6","B"])
        readLine(L3, ["7","8","9","C"])
        readLine(L4, ["*","0","#","D"])
        time.sleep(0.1)
except KeyboardInterrupt:
    print("\nApplication stopped!")

[aduroch]

Here is the Node Red related flow code:

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