Arduino: String to HEX String representaion for AT commands

Question

Sensors values:

float temperature = 29.5;
float humidity = 32.56;
float lightLevel = 17365.83;
int co2 = 452;
int noise = 583;

String dataString  = ""+String(temperature)+","+String(humidity)+","+String(lightLevel)+","+String(co2)+","+String(noise)+"";

The String will look like: "29.50,32.56,17365.83,452,583"

The hexstring would look like: "32392e35302c33322e35362c31373336352e38332c3435322c353833aa"

The modem I use will only accept AT commands and requires the data payload to be

payload in hexadecimal format strings (maximum length is 242 bytes)

Example Command: AT+SEND=1:1:32392e35302c33322e35362c31373336352e38332c3435322c353833aa

I am unable to create "AT+SEND=1:1:32392e35302c33322e35362c31373336352e38332c3435322c353833aa" programmatically in the Arduino.

How do you convert the dataString to the hexstring?

Where does aa at the end of the hexstring come from? It's not part of the original string. — gre_gor
– gre_gor, Commented Jun 24, 2024 at 18:15

gre_gor · Accepted Answer · 2024-06-24 18:18:06Z

0

You can make the serial interface convert string characters into their hexadecimal value representation.

void at_send(Print &serial, int port, int ack, String data) {
    serial.print("AT+SEND=");
    serial.print(port);
    serial.print(':');
    serial.print(ack);
    serial.print(':');
    for (int i=0; i<data.length(); i++) {
        if (data[i] < 16) { // ensure 2 characters per byte
            serial.print('0');
        } 
        serial.print(data[i], HEX);
    }
    serial.print("\r\n");
}

// then call as
at_send(Serial, 1, 1, dataString);

answered Jun 24, 2024 at 18:18

gre_gor

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