Data transfer tips

Tutorials
1

Hi all.
I’m new to the particle, I have a couple i’m setting up to get data from a cattle feedlot.
This is the stuff I couldn’t find on the forum:

Coding could do with a bit of work but it’s getting better.

Save a struct array to sd (sdFat)

for this struct (i know it’s huge)

    struct { 
    	uint32_t ts; // 4 bytes
    	int32_t wg[3]; // 12 bytes
    	uint64_t id[3]; // 24 bytes
    } rec[100]; 
 // total 40 * 100 = 4000 bytes (need to know these values for php script later)

stick some data in it

		rec[recCnt].ts = Time.now();
		rec[recCnt].wg[0] = newWeight[0]; rec[recCnt].wg[1] = newWeight[1]; rec[recCnt].wg[2] = newWeight[2];
		rec[recCnt].id[0] = id[0]; rec[recCnt].id[1] = id[1]; rec[recCnt].id[2] = id[2];
		recCnt++;

stick it on a sd card

		if (myFile.open(fileName, O_RDWR | O_CREAT | O_AT_END)) {
			myFile.write((uint8_t *)&rec, sizeof(rec)/sizeof(uint8_t));
		        myFile.close();
		}

get it back off the sd

	if (myFile.open(fileName, O_READ)) {
		while (myFile.peek() >= 0) {
			myFile.read((uint8_t *)&rec, sizeof(rec)/sizeof(uint8_t));
                        // send the data here and repeat till the sd is empty
            }
     }

send the data

  if (client.connect("www.my.website", 80)) {
    client.println("POST /receivedata.php HTTP/1.0");
    client.println("Host:  www.my.website");
    client.print("Stuff  "); // custom headers just go in
    client.println(stuffVar);
    client.print("Content-Length: ");
    client.println(sizeof(rec)/sizeof(uint8_t));
    client.println();
	client.write((uint8_t *)&rec, structSize);
    client.println();
    while (!client.available()) {
		if (cnt++ > 100) break;	delay(100); // timeout 10 seconds
	}
    while (client.available()) {
        reply = client.read(); // last char received is the reply from receivedata.php
    }
    client.stop();
  } else reply = '4';

In receivedata.php

$postContents = file_get_contents('php://input'); // the struct I sent
$cl = (int) $_SERVER['CONTENT_LENGTH']; // always 4000 but I check anyway
$stuffVar = $_SERVER['HTTP_STUFF']; // get my header

$structure = "";
for ($i=0;$i<($cl/40);$i++) { // 40 bytes each array member
	$structure .= "Lts" .  $i . "/L3w" .  $i . "/Q3id" . $i . "/"; // the structure of the struct
}
$pcArray = unpack($structure, $postContents); // the unpack array

// save the unpack array, it's a bit strange how unpack does the array, I use a for loop and make a new one
$pcString = json_encode($pcArray); 
$fileName = 'postContents.txt';
file_put_contents($fileName, $pcString, FILE_APPEND | LOCK_EX);

Pete

2

Is there any particular question you want answered?

But if you are looking for some general hint I’d do the assignment like this to save on typing

  rec[recCnt++] = { Time.now()
                  , { newWeight[0], newWeight[1], newWeight[2] }
                  , { id[0], id[1], id[2] }
                  };

or with a loop 0…2 filling wg[] and id[] in parallel.

3

Thanks for the tip, I didn’t think of that.

No, no questions, just thought it might help someone doing the same thing.

Pete

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