Review on HiLetgo HC-05 Bluetooth RF Transceiver Module - Wireless Master Slave Integrated Bluetooth Communication for Arduino with 6 Pin Wireless Serial Port Connection by Phillip Johnson

After searching the internet for how to use the HC-05, I ordered several for a project. I ended up getting the project working on the Arduino Uno. Designed a circuit board for the shield and made several blocks. Everything is working well. That's good news. The bad news is that it pays to be an electrical engineer with experience in embedded systems design. Various websites were helpful, but most of them had bugs. For example, some circuits didn't use a level switch to control the RxD input or read from the TxD. Some level switches are miswired and circuit selection can slow down even the highest data rates. Some Arduino Uno baud rates are not good choices due to clock errors. If you are running the HC-05 with the hardware serial number on the Uno, you will need to unplug the HC-05 to program the Uno. Other websites either don't understand the HC-05's two modes of operation, or at least describe them poorly. One mode (activated by pressing and holding the button) includes the configuration mode, which must be operated at 38400 baud. Once configured, the other mode (for data transfer) will operate at the baud rate selected during configuration. My project actually allows the Uno to turn on the device in configuration mode, verify the configuration, and then turn it on to restart in data mode. Don't reset your device every time you use it. This will likely burn the non-volatile memory that stores the parameters. Finally, Bluetooth itself can be tricky. I've found that Windows 7 and Windows 10 can be finicky about connecting and disconnecting a Bluetooth device. Good luck with your project. It may take some effort to get everything working. So far all modules have worked correctly after I have properly laid out the hardware and software.