You can easily change the baud rate of the HC-12 serial port but then you can 'lose' communicarions if the uC and HC-12 baud rate don't match.

One way out of this is to go through all available rates, send "AT" and look for "OK" response. This should work but is messy (IMO).

The other way, according to the datasheet, is to hold the 'SET' pin low when powering up the HC-12 and this should reset the default 9600 rate. However I cannot get this to work. Below is the sequence I have used. What am I doing wrong?

Hold SET low.
(delay)
Power up HC-12.
(delay)
Take SET high.
(delay)

[EDIT] For once Google has failed to give me any information on this though there is a vast amount of information on the HC-12.

 

I have now solved this conundrum. The sequence should be:
Hold SET low.
(delay)
Power up HC-12.
(delay)
Maintain SET low. The HC-12 interface will now be the defaut 9600, 8, n, 1
Send commands to configure the HC-12 as you wish.
Take SET high.
(delay)
The HC-12 will now be using whatever configuration you set.

 

hi Albert,
After reading your opening post, I did a web search and found a number of conflicting 'fixes' for the HC12 lock out.
Thanks for sharing a viable solution, I use a number of HC12's and its handy to know that fix.
Eric