使用PHP更新MySQL的Arduino变量失败

Question

I'm using a Serial to WiFi module which are able to send HTTP. I have made a sketch to update a Table in MySQL with a PHP script. My problem is, I'm not able to update the Table when using variables. It works fine with static values. I want to know if there is a problem in the Arduino sketch or the way to use the HTTP command.

Look at lines below from loop() and PHP script also:

 float tm = 21.8;

 Serial.write("AT+HTTPPH=/update1x.php?tmp=tm\n");  // Parse values to PHP script

If I insert the value 21.8 instead of variable tm, it works.

<?php

  $aa = (isset($_GET['tmp']) ? $_GET['tmp'] : null);

  mysql_connect('my.dk.mysql','my_dk','my_pw') or die("Can't connect that way!");

  @mysql_select_db('my_dk') or die("Unable to select a database called 'My'");

  date_default_timezone_set("Europe/Copenhagen");

  $dat = date("Y-m-d");

  $tim = date("H:i:s");

  $qry = "INSERT INTO temp1(temp, date, time) VALUES('$aa','$dat','$tim')";

  mysql_query($qry);

  mysql_close();

  exit('OK');

?>

Answer 1

because C does not "scan" the string and sobstitute "tm" with the value (think about what should happen all the time you used a variable called "i" or like...) C is a lot "lower" level, you have to concatenate by hand. actually a easy one may be:

Serial.print("AT+HTTPPH=/update1x.php?tmp=");
Serial.print(tm);
Serial.print("\n");

using String class is possible, but you will use RAM dinamically, witch is not advised on a microcontroller:

String s = "AT+HTTPPH=/update1x.php?tmp=";
s += tm;
s += "\n";
Serial.print(s);

note that i concatenate one string for line; that is because on the right we don't have object String, but C string: array of char. That is not valid for tm

also real C concatenation (what is appening inside String class can be found here: How do I concatenate const/literal strings in C?