Voltage divider for 3.3V HC-05 BT Module


I have a standard HC-05 Bluetooth Module for my Arduino Uno.

CIRCUIT: 5V on module to 5v pin or arduino GND on module to gnd pin on arduino TX on module to RX on arduino RX on module to TX on arduino (through voltage divider) KEY AND STATE ARE LEFT UNCONNECTED

I have read many tutorials and most say that I need to use a 10k and 20k Ohm resistor to get 5V signal from the Arudino down to 3.3 V so that the Bluetooth Module doesn't fry up.

I wonder if I could use a smaller value like 1k and 2k or something like that, or would that just short. Any help will be appreciated. Forgive me for the simple question for I am a beginner to the Arduino.

Thank you

Sure, if you don’t mind the higher current and power loss. You could do:

5V----///-----///----GND 1.66 mA
1k | 2k

For high speed logic 10k/20k is too slow - the rise times will be too slow.

However without knowing your baudrate its impossible to know if you are running at high speeds or not. use 1k/2k if not sure and battery life isn't an issue.

For really high speeds you'd use a level shifter circuit of some form.

Thank you for replying.

The battery life and runtime doesn't matter to me because it's powered of a wall adapter. The only concern I have is if it will damage the Arduino and will it work as a voltage divider.

You can use voltage dividers to level shift the signal lines.

You cannot use voltage divider between ground and 5v to get 3.3v and then power it off that, because voltage dividers depend on the current through both resistors being equal. The moment something is drawing current in the middle, you no longer have the voltage you thought you did - hence you cannot power things off of voltage dividers.

Most Arduino boards have a 3.3v regulator on board - if you're using one that doesn't, you'll need an LDO regulator (make sure dropout is no higher than 1.7v, otherwise it can't give you 3.3 from 5), not a voltage divider.

Thank you for replying. I did manage to get a working voltage divider with 1k and 2k Ohm resistors.