I just wanted to do a simple thing with the HC-12 module to test an idea... and I did it and this thing is working better than I expected!
This simple thing is RF spectrum analyzer whithin range 432.9-434.9MHz.
It consists a HC-12 and an OLED display(0.91") and a TC4056 li-pol charger module with a 100mAh rechargeable battery.
I used IAR STM8 Embeded Workbench IDE and wrote a new simple firmware for the STM8S003F3P6 microcontroller which placed on the HC-12 module and is driving an Si4463 tranceiver. This new device is very simple and have no many functions, but the result looks pretty well for this small and simple thing. Little change is needed on the HC-12 PCB to provide an I2C interface to OLED, you have to cut the line which connects GPIO 0 and PB4. Then the pins PB4 and PB5 of the STM8 chip just were directly connected to the contacts SCL and SDA of the OLED display accordingly.