Alex M0TOT has been challenging himself with more projects from the Instructables community. Here we have his implementation of Tom Heylen's experiment with a pair of Arduino Unos each fitted with HC-12 UHF wireless modules.
Alex notes that:
"In theory, the current, on the Rx, that can be sourced or sunk between Pin 13 and ground is 40 mA, but apparently that is for short periods only. It is recommended that it is kept at 20 mA - enough for an LED or a relay with a rated coil-power which is low. Anything else might require an optocoupler or transistor circuit."
And Tom writes in his article:
"In this instructable you will learn how to communicate between Arduinos over a long distance up to 1.8km in open air.
The HC-12 is a wireless serial port communication module that is very useful, extremely powerful and easy to use.
First you will learn how to make a wireless instant messenger with the least effort possible. Then we will move on to light up an LED with a push button and then you will learn a few useful string functions and operations for serial communication.
The last part of the instructable is not necessary but you will learn how to use the HC-12 module like a pro."
His project is fully documented here: https://www.instructables.com/Long-Range-18km-Arduino-to-Arduino-Wireless-Commun
and you can download the documentation (including the various Arduino sketches) here:
The HC-12 Wireless Module User Guide (v2.3B, as used in this project) with all the relevant AT commands is here: