This is the code for setting the channel of the HC-12 antenna on the MARS boards.

Open the serial monitor and type “AT”. If the module returns “OK”, the command mode is working.

Type “AT+Cxxx”.

The value can be a number from 001 to 127.

Every number is a 400KHz step. The working frequency of channel 100 is 473.0MHz.

Example: type “AT+C021”. The module returns “OK+C021”.

The module is now set to a working frequency of 441.4MHx

Note that both sending and receiving modules need to have the same frequency to communicate.

This can be FU1, FU2, FU4 or FU4 (FU4 at a baud rate of 1200 sets the chip to transmit up to 1800 meter in open air). See documentation for a full explanation.

Example: Type “AT+FU4”. The module returns “OK+FU4”.

Type “AT+RX”.

The module should return something like this:

“OK+FU3

OK+B9600

OK+C001

OK+RP:+20dBm”.

References:

https://www.instructables.com/Long-Range-18km-Arduino-to-Arduino-Wireless-Commun/

https://www.allaboutcircuits.com/projects/understanding-and-implementing-the-hc-12-wireless-transceiver-module/

Data sheet: https://www.elecrow.com/download/HC-12.pdf

https://howtomechatronics.com/tutorials/arduino/arduino-and-hc-12-long-range-wireless-communication-module/