ribbon cable wrong connection

Unable to control GPIO from the code

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I am using raspberry pi 4b along with Freenova kit. I am trying to make the LED blink however it does not blink instead it is ON of the time. I have tried different code (C,Python,Java) but none of it seems to work. What am I doing wrong? below is my Java code that I execute in Processing. None of it works, why? I want Java code the most.

import processing.io.*;
int ledPin = 17;
//define ledPin
boolean ledState = false;
//define ledState
void setup() {
    size(100, 100);
    //set frame rate
    GPIO.pinMode(ledPin, GPIO.OUTPUT);
    //set the ledPin to output mode
void draw() {
    ledState = !ledState;
    if (ledState) {
        GPIO.digitalWrite(ledPin, GPIO.HIGH);
        //led on
        background(255, 0, 0); //set the fill color of led on
    } else {
        GPIO.digitalWrite(ledPin, GPIO.LOW);
        //led off
        background(102); //set the fill color of led off

Python code:

import RPi.GPIO as GPIO
import time

ledPin = 11    # define ledPin

def setup():
    GPIO.setmode(GPIO.BOARD)       # use PHYSICAL GPIO Numbering
    GPIO.setup(ledPin, GPIO.OUT)   # set the ledPin to OUTPUT mode
    GPIO.output(ledPin, GPIO.LOW)  # make ledPin output LOW level 
    print ('using pin%d'%ledPin)

def loop():
    while True:
        GPIO.output(ledPin, GPIO.HIGH)  # make ledPin output HIGH level to turn on led
        print ('led turned on >>>')     # print information on terminal
        time.sleep(1)                   # Wait for 1 second
        GPIO.output(ledPin, GPIO.LOW)   # make ledPin output LOW level to turn off led
        print ('led turned off <<<')
        time.sleep(1)                   # Wait for 1 second

def destroy():
    GPIO.cleanup()                      # Release all GPIO

if __name__ == '__main__':    # Program entrance
    print ('Program is starting ... \n')
    except KeyboardInterrupt:   # Press ctrl-c to end the program.

C code:

#include <wiringPi.h>
#include <stdio.h>

#define  ledPin    0    //define the led pin number

void main(void)
    printf("Program is starting ... \n");
    wiringPiSetup();    //Initialize wiringPi.
    pinMode(ledPin, OUTPUT);//Set the pin mode
    printf("Using pin%d\n",ledPin); //Output information on terminal
        digitalWrite(ledPin, HIGH);  //Make GPIO output HIGH level
        printf("led turned on >>>\n");      //Output information on terminal
        delay(1000);                        //Wait for 1 second
        digitalWrite(ledPin, LOW);  //Make GPIO output LOW level
        printf("led turned off <<<\n");     //Output information on terminal
        delay(1000);                        //Wait for 1 second

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pythonpi-4ledjavacshareedit  follow  close 2flagedited Nov 2 at 13:27asked Nov 2 at 12:06newbie322 bronze badges

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1 Answer


Your code and breadboard wiring looks fine to me. Your Python code works on my Pi.

I suspect your ribbon cable is the wrong way round either at the Pi end or the breadboard end. Your T Cobbler board could also be faulty.

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shareedit  follow  flag answered Nov 2 at 12:53CoderMike4,52711 gold badge77 silver badges1515 bronze badges

  • 1I have added more pictures, on one it is on but doesn’t flash, on the other one it is not even on. Do you have raspberry pi 4b a swell? – newbie Nov 2 at 13:23
  • 1Yes, this is a Pi4B. – CoderMike Nov 2 at 13:25
  • 1Your 3rd photo (LED on) – the cable at the Pi end is wrong. – CoderMike Nov 2 at 13:29 
  • 1so I assume that on 2nd photo it is connected correctly (It is connected like that at the moment), why led doesn’t work at all then? – newbie Nov 2 at 13:30
  • With the ribbon cable as in your 2nd photo – you may need to turn the LED around. They only work in one direction. – CoderMike Nov 2 at 13:30 
  • 2Thanks Mike for your help 🙂 – newbie Nov 2 at 13:37
  • @CoderMike, your advice is very good to newbies. You remind me of my bad experience of frying two Rpi Sensor hat is a row. It is about what you suggested to check “Is your ribbon cable connected wrong way round?” I have been playing with ribbon cable for years, keyed or not keyed, factory made, custom made, DIYed, long or short, 4/10/26/40 pin one. So I was over confident when try to use a long ribbon cable to extend my sensor board from Rpi. It is only after I fried all my two sensor boards (I usually order two, one for spare, sort of “second source/pair/swap”). / to continue, … – tlfong01 8 mins ago   
  • I stupidishy wrongly thought that of course I know the meaning of the red coloured wire of the 40 pins wire, but I did realised that even the coloured red assures one pin is on the correct side, there is NO guarantee that the other 39 pins are in correct order, because I might have “twisted” the up/down position. Anyway, I learned my lesson. I placed the two fried sensor boards (very expensive to a poor hobbyist like me!) in my “mistake junk box”, to remind me to think twice before I leap. Just thinking aloud, sorry for all the uncorrected grammatical and spelling mistakes. – tlfong01 just now   Edit   

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