Reading a pin state ?!

Using Arduino Programming Questions
#1

hi! i've got a simple project that turns digital pins on and off to control a relay board.

am i correct in thinking that i cannon use digitalRead to find out the current state of the pins? as they are set to outputs to drive the relays....

id like to know the pin state so i can output an "ON" or "OFF" to my i2c display
cheers onis

#2

digitalRead () works anytime on any pin.

#3

ah I see, does it return a value like 1 for on and 0 for off ?

#4

MarkT:
digitalRead () works anytime on any pin.

But if you’re the one doing the digitalWrite()s so you already know the state; you’re in charge of it.

#5

how would i code it then ? do i need to change a stored variable each time i use digitalWrite() ??

then later in the sketch when im writing to the the lcd i can read that variable ?

#6

onisuk:
how would i code it then ? do i need to change a stored variable each time i use digitalWrite() ??

then later in the sketch when im writing to the the lcd i can read that variable ?

That would work yep.

#7

do i need to change a stored variable each time i use digitalWrite()

A better way is to always use the state variable in the digital write

boolean state = true;
digitalWrite(pin, state);
#8

ah so what is that doing ? when the digital pin is written high the boolean called "state" is then updated to true ?
and the opposite happens when its low ?

#9

basically ive got an RTC clock that reads the time and turns on a relay to put on a light …

//Light control
if (hour() > 7 && hour() < 20)
{
digitalWrite(lightPin, HIGH);
}
else
{
digitalWrite(lightPin, LOW);
}

this is my code so how do i read the state of “lightPin” so i can output to my display ?

all this help is very much appreciated

#10

when the digital pin is written high the boolean called “state” is then updated to true ?

No nothing is updated. By simply writing the variable and then manipulating your variable you keep the two in sync.

so how do i read the state of “lightPin” so i can output to my display ?

You do not read it. You use the state variable to keep track of it.

 if (hour() > 7 && hour() < 20)
    {
      state = HIGH;
      digitalWrite(lightPin, state);
    }

    {
      state = LOW;
      digitalWrite(lightPin, state);
    }

The variable state is the state of the pin who’s value is given by the variable lightPin.

#11