backlight LED works backwards?

Hello,

I'm testing the arduino, trying to read input CH2, and consequently turn on backlight (pin 13), turn on LED attached to CH3, and update LCD.

However the backlight seem to go on when CH3 is off and vice versa.

here's the code:


#include <UC1701.h>
#include <Wire.h>
#include <Indio.h>
static UC1701 lcd;


void setup() {

  lcd.begin();
  Indio.digitalMode(2,INPUT);  // Set CH2 as an input
  Indio.digitalMode(3,OUTPUT);  // Set CH3 as an input
  pinMode(13,OUTPUT); // 13 is the backlight
  lcd.setCursor(0, 1);
  lcd.print("channel 2");
}

void loop() {

  // check if the pushbutton is pressed.
  // if it is, the CH2 button is HIGH:
  if (Indio.digitalRead(2) == HIGH) {
    // turn LED on:
    digitalWrite(13, HIGH);
    Indio.digitalWrite(3, HIGH);
    // and write high
    lcd.setCursor(64, 1);
    lcd.print("high");
  }
  else {
    // turn LED off:
    digitalWrite(13, HIGH);
    Indio.digitalWrite(3, HIGH);
       lcd.setCursor(64, 1);
    lcd.print("low ");
  }
}

am I doing something wrong?

alessandro netzer
alessandro netzer
12
| 1 0 1
Asked on 6/16/15, 11:47 PM
1
vote
998 Views

I see in your code that you write "HIGH" to D13 twice, basically keeping the backlight off. So to make it work you need to change it to "LOW" in the first "if" routine.

Loic De Buck
on 6/17/15, 5:00 AM

Yeah, i made a mistake when copying the sketch here, actual code said Low on both LEDs in the "else" clause. 

Thanks for the reply!

alessandro netzer
alessandro netzer
12
| 1 0 1
Answered on 6/17/15, 12:09 PM
0
vote

Hello Alessandro, Yes that is correct, the backlight works inverse because it is switched by a PNP transistor. Best Regards, Loic

Loic De Buck
Loic De Buck
1237
| 3 1 3
Answered on 6/17/15, 4:50 AM
0
vote

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Asked: 6/16/15, 11:47 PM
Seen: 998 times
Last updated: 6/17/15, 12:09 PM