Here’s a fun one for you. It’s a major thorn, as it’s affecting nearly all the deployed devices in this config - over time. They start off working fine, but they eventually (anywhere from 30 minutes to a month later) end up bricked.
I took a “brick” back for diagnosis, and found that it did indeed produce serial data output. Not at the defined 9600 baud, but instead back at 57600 baud. Except it wasn’t completely factory-reset… it was still using DHCP, and that worked fine. It forgot who to connect to (so it didn’t establish a connection). But more importantly… it set its own random-garbage “search key”, so it doesn’t respond to ConfigTool scans.
I managed to get it into serial command mode by holding the HW_TRIG pin low during power-up (indicated by “LGHWSWITCHOK”). Then, I asked it for its config details…
So, what caused this random memory store corruption? Is there a way to keep this thing from ever changing/resetting its config? Should the HW_TRIG pin be tied high?
We only use 3 pins - Rx, Tx, Reset (floating normally, pull-down to activate; noise reduction by adding 0.1uF cap between VCC and Reset). No flow control, no other pins. This is the TTL (3.3v) version - though driven by 5v logic (an unfortunate compromise we really couldn’t avoid, but seems to work). Do the unused pins need to be tied somewhere?