Sending data to ThingSpeak API from device but channel is not updated -- what changed? | Page 2 | Announcements | Forum

A lot of the code pattern that we see the problem with looks like this:

WiFiClient client;

...

void loop() {
if (client.connect(server, 80)) {

// Read some sensor

// Construct API request body
String body = "field1=";
body += String(sensorValue);

client.println("POST /update HTTP/1.1");
client.println("Host: api.thingspeak.com");
client.println("Connection: close");
client.println("X-THINGSPEAKAPIKEY: " + writeAPIKey);
client.println("Content-Type: application/x-www-form-urlencoded");
client.println("Content-Length: " + String(body.length()));
client.println("");
client.print(body);
}

client.stop();
}

Notice the problem is that there is zero time between the POST request and the closing of the connection using client.stop(). Ideally, the code would read back the response and confirm it is a HTTP 200 status code.

This is done in the ThingSpeak library (https://github.com/mathworks/thingspeak-arduino) in the getHTTPResponse() method. See https://github.com/mathworks/thingspeak-arduino/blob/master/src/ThingSpeak.h for the implementation.

If that is not do-able, a simple insertion of delay(250); immediately after client.print(body); should suffice. Again, the delay is not the solution I would recommend, but, it is the smallest code change required to prevent the above code pattern from running into trouble.