Agree.. I was dumb to connect the Bluetooth module directly from Vcc.
I do hope you see why the voltage divider won't work.........With 1ma source, 2K will be at 2V at the top. This maybe enough to partially turn on the transistor to themotor, when it should be off.When the Arduino pulls down, there well be 1V at thetop of the divider. Again, that may not be enough toproperly turn on the drive, causing more power lossin the drive transistor.........
..Now, you connect 12V. Again, not knowing the circuitattached, the 2:1 divider could be putting 6V on theArduino.Dwight
I don't know WHICH Vcc you are referring to. ...What I meant was that your battery (regardless of the voltage as long as it is <12V) should be connected to "VIN" of the arduino (the input for the onboard 5V regulator).. .....I have no idea if they are NPN or PNP but the OP says the motor turns on when those control lines are grounded , suggesting PNP transistors on the heat sinks. I have repeatedly asked the OP to look at the numbers on the power transistors but my requests have fallen on deaf ears.