Declaring a variable for timeStr()?

Firmware
1

I’m setting up a system to monitor water tanks back to a web page. I have a lot of the Photon FW and even some of the html/js figured out. I would like to pass a timestamp from Photon back to the web page so the user can see if there has been any significant delay since the last update. I don’t need to do any manipulation. Just read it and pass it.

There may be a better way to do this. If so, I am open to suggestions,but if not, I am having a hard time figuring out how to declare a variable to receive timeStr() so I can pass it back to the web page.

As far as I can tell from reading everything I can find - timeStr() returns a string. How do you declare a string variable on the Photon? Or, how can I set up a variable to receive timeStr()? I have tried declaring various forms of char, but get compile error messages complaining about mixing char and string variables.

Thanks for your help

2

Not directly answering the question, but if you’re using the publish system, there’s a time-stamp included.
As far as strings go: https://docs.particle.io/reference/firmware/photon/#string-char-array

3

Thanks Moors7. I should have been more clear. I’m passing the variable using Particle.variable() in the FW and using $.get in the js code.

After looking again more closely at your link, I found that if I declared char CheckTime[26]; then did String CheckTime = Time.timeStr(); it actually compiled.

Now back to html/java to see how the variable shows up there.

Thanks again.

4

@Cloudy,

Did this work for you using a Particle.variable? It compiles for me as well but the Particle.variable() does not return the time.

5

How are you trying?

Particle.variable() cannot expose the return value of a function call.
It’s only meant to expose the values of global variables (strings, int and double - I’ve learnt some time ago - although undocumented - console also understands bool).

6

@ScruffR,

As you know, I am working to add code to my devices to change with the upcoming switch away from Daylight Savings Time. I would like to have a variable I could check to ensure that the device is on the right time. Ideally, this would be a Particle.variable() I could query.

First, I tried the approach in this thread.

I defined a global variable - char CheckTime[26];
defined a Particle.variable("Offset", CheckTime);
and in Setup, I calculated the value - String CheckTime = Time.timeStr();

When I accessed this variable in the console - it had no value. This is why I posted my question to @Cloudy.

What ended up working was:

I defined a global variable - char currentOffsetStr[10];
defined a Particle.variable("Offset", currentOffsetStr);
In setup, I have these two lines:

float currentOffset = (Time.local() - Time.now()) / 3600.0;
snprintf(currentOffsetStr,sizeof(currentOffsetStr),"%2.1f UTC",currentoffset);

This gives a value of "-4 UTC" which is the correct value.

Open to suggestions on why the first approach does not work.

Thanks,

Chip

7

If you did this, then you have created a local variable which hid the global variable and hence the global never actually got set.
Just leave out the String (variable type introducing the redeclaration) in your assignment.

// either (my preference avoiding String)
char CheckTime[26];
void setup() {
  strcpy(CheckTime, Time.timeStr());
  Particle.variable("Offset", CheckTime);
}
// or when using String (... shudder ... ;-)
String CheckTime;
void setup() {
  CheckTime = Time.timeStr();
  Particle.variable("Offset", CheckTime);
}
1 Like
8

@ScruffR,

Thank you, I appreciate you setting me straight - again. I also appreciate the reminder not to use String.

Chip

1 Like