Review on DSD TECH HC-05 Bluetooth Serial Pass-through Module: Seamless Wireless Serial Communication with Arduino Button by Vincent Pavelko

It took me about 6 hours to figure out how to communicate with him via AT. Had to go through numerous white papers DSD, Youtube etc. ** Please note that a slow 2 second ON/OFF LED means it is in AT mode. *** They are also in slave mode by default and need to be configured via AT to be paired. **** It is recommended that the RXD pin has a voltage divider, I use 1.8kΩ and 3.3kΩ. Now that it's working for me, it's pretty reliable. I have 2 Arduinos communicating with 2 DSD Tech HC-05. I had to connect the slave VCC to a 5V relay in case it lost connection to the master. If it loses connection I just open the normally closed relay switch through the Arduino and then close it again for another 10 seconds. After solving this connection problem, I was able to establish a stable connection (the relay probably trips once or twice an hour). Spring.