Arduino read from Server periodically

Question

I have an arduino attached with a RGB-Shield. I want to query my server for the RGB values periodically. I basically got it working using the Ethernet Shield but it takes too long to get the value (~500ms}. I really want to read the values from my server really really fast in an endless loop.

Can you give me any hints on how I can improve my code?

#include <SPI.h>
#include <Ethernet.h>
byte mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED };
IPAddress server(192,168,1,151); 
IPAddress ip(192, 168, 1, 177);
EthernetClient client;
void setup() {
 Serial.begin(9600);
 while (!Serial) {
 ; // wait for serial port to connect. Needed for Leonardo only
 }
 // start the Ethernet connection:
 if (Ethernet.begin(mac) == 0) {
 Ethernet.begin(mac, ip);
 }
 delay(1000);
 if (client.connect(server, 80)) {
 client.println("GET /rgb.php HTTP/1.1");
 client.println("Host: 192.168.1.151");
 client.println("Connection: close");
 client.println();
 }
 else {
 Serial.println("connection failed");
 }
}
void loop()
{
 if (client.available()) {
 char c = client.read();
 ... read from Server 
 }
 if (!client.connected()) {
 client.stop();
 if (client.connect(server, 80)) {
 client.println("GET /rgb.php HTTP/1.1");
 client.println("Host: 192.168.1.151");
 client.println("Connection: close");
 client.println();
 } 
 }
}

• Jossef Harush Kadouri: you may use mqtt protocol, it support push notifications instead of polling and it's way lighter
• matthias: Yeah I thought about that, but I could not imagine that push is faster than polling. Is it?

Answer 1

You could try with a direct TCP connection (in this way you skip the HTTP layer) but you need to prepare also a small TCP server (in any language comfortable to you) that accepts the client connection, sends the data, waits the ACK and close the connection.

Answer 2

I would start with this section:

if (client.connect(server, 80)) {
 client.println("GET /rgb.php HTTP/1.1");
 client.println("Host: 192.168.1.151");
 client.println("Connection: close");
 client.println();
}

How many messages does the Arduino Ethernet library send for this block? Actually due to the implementation of the Arduino Print and EthernetClient class it sends 7 messages (no joke!). It does not collect this into a single message/frame.

The first optimization is to print a single string and send that as one frame.

 #define CR "\r\n"
 client.print("GET /rgb.php HTTP/1.1" CR
 "Host: 192.168.1.151" CR
 "Connection: close" CR
 CR);

Cheers!