We have had our HC-05 working well for the past two weeks but as of today, it will no longer talk to our phones through MIT App Inv. We are concerned that the HC-05 is dead/fried.
At one point the students had the RX pin on the BT connected directly to the TX pin on the Nano Every without the voltage divider resistors hooked up correctly. I assume that we were sending a 5v signal into the 3.3v RX pin. It wasn't that way for very long but we are worried it might have been "long enough."
We have also been pulling the RX wire when uploading into the arduino from the computer (but probably not every time we upload). Not sure if that makes the BT angry or not but several websites have recommended pulling the wire when uploading.
Now when we power up the BT we get three blinks in about 2 second from the onboard LED then about a one second pause before it blinks three times again. Sometimes this goes on for a while and sometime it cycles 2 or 3 times before the led just goes dark. We can no longer connect to the HC-05 through App Inventor or even in the BT menu on the phone itself.
The MIT app seems to be fine and the arduino seems to be fine.
We've been looking for a HC-05 blinking light code explanation online without much success.
We did run into some issues getting multiple serial devices to work at once, you may have written data to it while trying to communicate with another serial device. Did you reset the module ? Here's a good link I found that talked about blink codes and how to reset.
https://forum.arduino.cc/t/bluetooth-hc-05-keep-blinking/326827/5
It would not be the first (nor last) device to get fried while prototyping.
Don
The bluetooth modules I've used have generally been 5v tolerant on the RX/TX pins. I've used many without using a resistor. So, that unlikely to have fried the module. Same for uploading code from the computer.
