A couple of weeks ago I posted a discussion about using a Bluetooth HC-05 module to control one of my WALL CLOCKs. One of the issues I faced was not being able to reliably control one of the two modules that I purchased using AT commands. One worked while the other didn’t and I couldn’t figure out why.
So, with a little bit of time to kill, and a very helpful instructable, I tried to get the errant unit into AT-mode. Again, no luck!
While there are many discussions online about this issue, I could not find one that related specifically to the module I had. In my case the mode select pin of the HC-05 daughter board is not brought out to the pins of the carrier. But by tracing the layout, I worked out how to wrestle this little bugger into AT command mode and reset the unit to its factory default settings. Thank Odin for Internet!