There are two typical bluetooth modules I’ve been playing around with. the HC-05 and the HC-06. The difference between the two is that the HC-05 can be used as both a Master or a Slave, while the HC-06 can only be used as a Slave. This means the HC-05 can initiate a connection and receive a connection while the the HC-06 can only receive a connection. More info on the boards and their differences.
These boards basically work as a wireless SERIAL port for your arduino.
Note to self:Add links or examples to the two code solutions for using these boards with arduino. There’s the simulated serial port and the direct serial pin connection.
They’re designed for 3.3 volts while the logic on an arduino is typically a 5 volt board. This means that in order to properly use these bluetooth boards with an arduino you’ll require a voltage divider circuit between the arduino and the RXD pin on the bluetooth circuit. This is basically 3 resistors of identical resistance with your RXD wire connected between the first resistor closest to the arduino pin and the other two resistors connected to ground.
Typically, if you check the aliexpress pages for these boards you’ll be told that you can reprogram them as long as they’re not paired up to anything, but what I’ve found is that there are some hoops that need to be jumped through first. Those hoops and the necessary wiring is documented here.