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Topic: Using the time library... (Read 459 times) previous topic - next topic


Oct 28, 2013, 09:14 pm Last Edit: Oct 29, 2013, 09:37 pm by rcrowen Reason: 1
Basically what I'm trying to do:
1. On button press, print the current date and then the date x amount of time later (which will depend ultimately on the choice of four different buttons, in this case I was trying for two days later).

2. Not sure how exactly I tell day() to add a value. My attempt did not work.


Code: [Select]

 This is an Arduino library for the Adafruit Thermal Printer.
 Pick one up at --> http://www.adafruit.com/products/597
 These printers use TTL serial to communicate, 2 pins are required.

 Adafruit invests time and resources providing this open source code.
 Please support Adafruit and open-source hardware by purchasing products
 from Adafruit!

 Written by Limor Fried/Ladyada for Adafruit Industries.
 MIT license, all text above must be included in any redistribution.

// If you're using Arduino 1.0 uncomment the next line:
#include "SoftwareSerial.h"
// If you're using Arduino 23 or earlier, uncomment the next line:
//#include "NewSoftSerial.h"

#include "Adafruit_Thermal.h"
#include "adalogo.h"
#include <avr/pgmspace.h>
#include <Time.h>

int printer_RX_Pin = 5;  // This is the green wire
int printer_TX_Pin = 6;  // This is the yellow wire
const int buttonPin = 2;   // the number of the pushbutton pin
int foodType = 1;

int buttonState = 0;  // variable for reading the pushbutton status

Adafruit_Thermal printer(printer_RX_Pin, printer_TX_Pin);

void setup(){
 pinMode(7, OUTPUT); digitalWrite(7, LOW); // To also work w/IoTP printer
 // initialize the pushbutton pin as an input:
 pinMode(buttonPin, INPUT);

void printDigits (int digits) {
  // utility function for clock display: prints preceding colon and leading 0
  if(digits < 10)

void loop(){
 // read the state of the pushbutton value:
 buttonState = digitalRead(buttonPin);

 // check if the pushbutton is pressed.
 // if it is, the buttonState is HIGH:
// This prints the current date
 if (buttonState == HIGH) {        
 printer.println(" ");
 printer.println(" ");
 printer.println(" ");

// This statement updates the date depending on type of food i.e. Vegetable, meat, etc.
 if (foodType == 1) {
   day = day + 2;
   printer.println("Use by this date: ");

 printer.sleep();      // Tell printer to sleep
 printer.wake();       // MUST call wake() before printing again, even if reset
 printer.setDefault(); // Restore printer to defaults  


Specifically, I'm talking about my if statement in which I have the code in question currently commented out. Thoughts?

The code does (did) something. What that is is a mystery.
You want the code to do something. What that is is a mystery.

My thought is that you need to finish asking your question.

Code: [Select]
     // This prints the current date of fridge going into fridge
This does what?

Code: [Select]
  if (foodType = 1) {
= != ==

The art of getting good answers lies in asking good questions.


Thanks for the response. Updated original to hopefully make a little clearer.


Jack Christensen

It's worth reading about the Time library and also looking through the actual code (specifically the Time.h and Time.cpp files).

The Time library defines a couple new data types that you will want to be familiar with.  It also defines a bunch of functions for working with these data types.

The time_t data type represents a particular point in time, to a resolution of one second.  Specifically, the value held in a time_t variable is just the number of seconds since 00:00:00 01Jan1970 (the Unix epoch; the Arduino Time library has a lot in common with the standard C time library).

Actually time_t is just an unsigned long integer.

To conveniently determine the month, day, year, hour, minute or second represented by a time_t variable, there are a bunch of functions that are explained on the page linked above.

Not documented at the link above is another data type called tmElements_t.  This is actually a structure that has different members representing year, month, day, etc.  Then there are two functions for converting between a time_t variable and a tmElements_t structure, makeTime() and breakTime().

Very useful library once you get the hang of it.  Have a look, then if you don't get it, ask questions.

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