Is boolean digital input value 'LOW' transferable?

Using Arduino Programming Questions
1

If a digitalRead returns a boolean 'LOW' value is that 'LOW' value able to be transferred as 'LOW' or does it become a numeric '0' value? Will 'relay_state' be interpreted as 'LOW' or '0' in the code below?

cpp
  int debounceDelay = 50;

  current_relay_input = digitalRead(relay);
  if (current_relay_input != previous_relay_input) {
    RelayLastDebounceTime = current_Millis;
  }
  if (current_Millis - RelayLastDebounceTime > debounceDelay) {
    relay_state = current_relay_input;
    previous_relay_input = current_relay_input;
  }

  if (relay_state == LOW) {       //  should I check for LOW or '0'?
   Serial.print(" do something....");
  }
2

I don't see a boolean in your code.

digitalRead() returns HIGH or LOW, not a boolean (true or false). Those might or might not be 0 and 1.

3

booleans are either 'true' or 'false'

The actual value returned on an Uno is set by these defines:

digitalRead() returns an int:

4 
void setup() {
   Serial.begin(115200);
   Serial.print("0 == LOW is ");
   if( 0 == LOW ) {
      Serial.println("true");
   } else {
      Serial.println("false");
   }
   Serial.print("0 == false is ");
   if( 0 == false ) {
      Serial.println("true");
   } else {
      Serial.println("false");
   }
   Serial.print("LOW == false is ");
   if( LOW == false ) {
      Serial.println("true");
   } else {
      Serial.println("false");
   }
}

void loop() {
}

Connecting to /dev/ttyACM0. Press CTRL-C to exit.
0 == LOW is true
0 == false is true
LOW == false is true
5

I probably should be more skeptical of what Google Chrome's AI provides then. lol...

6

I'm with

even though I write most times relying on LOW to be 0 or flase, and HIGH non-zero or true.

Because we can't be allowed to know that.

You can capture a switch this way

  bool switchIsPressed = digitslRead(somePin) == LOW;

Which cleanses things a bit and gives you a real true or false to use.

You can just

  if (digitslRead(somePin) == LOW) {

which I hope is obvious.

a7

2 Likes
7

From the AVR core (e.g. Uno).

int digitalRead(uint8_t pin)
{
	uint8_t timer = digitalPinToTimer(pin);
	uint8_t bit = digitalPinToBitMask(pin);
	uint8_t port = digitalPinToPort(pin);

	if (port == NOT_A_PIN) return LOW;

	// If the pin that support PWM output, we need to turn it off
	// before getting a digital reading.
	if (timer != NOT_ON_TIMER) turnOffPWM(timer);

	if (*portInputRegister(port) & bit) return HIGH;
	return LOW;
}

And LOW and HIGH are defined in Arduino.h

#define HIGH 0x1
#define LOW  0x0

From the megaAVR core (Nano Evevry and Uno WiFi Rev2)

PinStatus digitalRead(uint8_t pin)
{
	/* Get bit mask and check valid pin */
	uint8_t bit_mask = digitalPinToBitMask(pin);
	if(bit_mask == NOT_A_PIN || isDoubleBondedActive(pin)) return LOW;

	// If the pin that support PWM output, we need to turn it off
	// before getting a digital reading.
	turnOffPWM(pin);

	/* Get port and check valid port */
	PORT_t *port = digitalPinToPortStruct(pin);

	/* Read pin value from PORTx.IN register */
	if(port->IN & bit_mask){
		return HIGH;
	} else {
		return LOW;
	}
	return LOW;
}

And PinStatus is defined in Common.h

typedef enum {
  LOW     = 0,
  HIGH    = 1,
  CHANGE  = 2,
  FALLING = 3,
  RISING  = 4,
} PinStatus;

Please note the difference in the return value of the digitalRead() function.

1 Like
8

The way I was taught, is that a zero value is false, and any non zero value is true.
No matter what variable type.

9

I like this approach as it enables me to pass a "true" or "false" value instead of trying to know with certainty what 'LOW' represents. All of this was precipitated by trying to employ debounce code for some digital inputs where the relat contacts were 'bouncing' on the physical change of state. I was picking it up in the array structure where I could see the fast change of state being recorded.
But the debounce code seemed to be misinterpreting the 'LOW' value. At any rate going with your suggestion should clean things up. :+1:

10

Another thing you might like to start adding is

# define PRESSED LOW      // switch is pulled up

then later

  bool switchIsPressed = ditigalRead(somePin) == PRESSED;

which makes for readable code, and one place to change how you wired your switches should it come to that.

There is an equivalent set of things to know and keep in mind around digitalWrite(), which again technically should only be passed LOW or HIGH for the value to put on the pin.

# define ON HIGH

for example.

a7

1 Like
11

I/O pin state LOW = numerical 0 = boolean false = bit cleared.
I/O pin state HIGH = numerical 1 = boolean true = bit set.
+

lastchancenameRelentless optimist, or too dumb to be a pessimist

1hpost #8

The way I was taught, is that a zero value is false, and any non zero value is true.
No matter what variable type.

12

That is an excellent tip!

My code is so convoluted it is embarrassing talking with those who write on a pro level. But the good thing is as I learn more I am able to go back and rewrite the stuff that is unreadable. If it works logically great but if you have to come back six months later and do something else it really helps if it is in a presentable form. Probably 50% of my code would be considered superfluous/unnecessary by anyone with a high level of programming skills. ...lol...