help with millis()

Projects Programming
1

I am trying to make an rfid safe. I am using a finite state machine to have 3 states: locked, unlocked, and reprogramming. In the locked state, the arduino scans for either a button press, which changes the state to reprogramming, or a card read by the rfid reader, which changes the state to unlocked if it matches the authorized code stored in eeprom. In the unlocked state, the arduino waits 3 seconds, then relocks the safe and changes its state to locked. In the reprogramming state, the ardsuino stores the next card to be scanned in eeprom (this feature changes the card authorized to open the safe). If no card is scanned within 5 seconds, the state is changed back to locked. To execute the 5 second timeout, i am using millis(). In the code, i had the arduino print "reprograming..." to the serial monitor when the button is pressed, and "locked" when the 5 second timeout is over. The problem is, when the button is pressed, the serial monitor prints "reprogramming...", then "locked" in a cycle that runs 4-5 times in about a second. If the button is held down, it continues the cycle until the button is released.

#include <EEPROM.h>
#include "EEPROMAnything.h"
int val = 0;
char code[11]; //the code read by the RFID reader
char validCode [11]; //code read from EEPROM is stored here
int bytesread = 0;
#define buttonPin 10
int lockState = 0;
unsigned long time;

void setup(){
Serial.begin (2400);
pinMode(2,OUTPUT);
pinMode (buttonPin, INPUT);
digitalWrite(2, LOW);
EEPROM_readAnything (0, validCode);
}

bool readRFID(){
if(Serial.available() > 0) { // if data available from reader
if((val = Serial.read()) == 10) { // check for header
bytesread = 0;
while(bytesread<10) { // read 10 digit code
if( Serial.available() > 0) {
val = Serial.read();
if((val == 10)||(val == 13)) { // if header or stop bytes before the 10 digit reading
break; // stop reading
}
code[bytesread] = val; // add the digit
bytesread++; // ready to read next digit
}
}
if(bytesread == 10) { // if 10 digit read is complete
bytesread = 0;
digitalWrite(2, HIGH); // deactivate the RFID reader for a moment so it will not flood
delay(1500); // wait for a bit
digitalWrite(2, LOW); // Activate the RFID reader
return true;
}
}
}
return false;
}

void loop() {
switch (lockState)
{
case 0: //Locked State
if (digitalRead (buttonPin) == LOW) // check if the button is pressed
{
time = millis();
lockState = 2;
Serial.println ("Reprogramming...");
break;
}
else if(readRFID()== true)
{
if (strcmp (code, validCode) == 0)
{
//unlock...
lockState = 1;
break;
}
}

break;
case 1: //Unlocked State
digitalWrite (2, HIGH);
Serial.println ("Unlocked");
delay (3000);
Serial.println ("Locked");
digitalWrite (2, LOW);
//lock...
lockState = 0;
break;
case 2: //Reprogram
if (time + 5000 >= millis())
{
Serial.println ("Locked1");
lockState = 0;
break;
}

else if (readRFID())
{
//EEPROM_writeAnything (0, code);
Serial.println ("Locked");
lockState = 0;
break;
}
//break;
}
}

the nature of the problem suggests (to me) that the code is performing the actions inside the

if (time + 5000 >= millis())

statement even when the condition is not true. How can I fox this problem? Is it my code, or is something wrong with my chip? please help...if you have any questions, please ask.

2

I would write it as:

if (time - buttonPressTime >= 5000) {
....

time should be updated every time through the loop, and buttunPressTime should be updated when the button is pressed.

3

This
if (digitalRead (buttonPin) == LOW) // check if the button is pressed
suggests your button connects to Gnd when pressed.

This
pinMode (buttonPin, INPUT);
says you are not utilizing the internal pullup.
Change to
pinMode (buttonPin, INPUT_PULLUP);
to ensure the pin is not floating and leading to what would appear as false low readings and the repeated actions you see.

4

I already have a pull up resistor. And could someone please elaborate on Canyonero's response?

6

So for Canyonero's fix, I know I set "buttonPressTime" when the button is pressed, but when do I set "time"?

7

do a time = millis(); that gets called every time you go through the loop, and stays (relatively) current, make it the first line in your loop.

Then you can do a buttonPressTime = time; when the button is pressed.

8

Or just use millis() instead of time.

9

Thanks everyone. I got it to work.

10

What did you change?

11

I used the easier method and changed the greater than to a less than