It maintains the voltage level required by Bluetooth radio chip (3.3v) up to certain fluctuation limit in input voltage. The voltage gets regulated automatically and is made within the permissible range.

Bluetooth modules operate at 3.3v.if we provide voltage more at 3.3v then there is a case it might burn out.

For the HC-05 RX pin (data in) we need to convert the Arduinos 5V to 3.3v. A simple way to do this is by using a voltage divider made from a couple of resistors. In my case I use a 1K ohm resistor and a 2K ohm resistor or we can use voltage regulator to regulate the input voltage.

The voltage regulator that is used in HCO5 is 662K is a low dropout regulator which can regulate the output voltage even when the supply voltage is very close to the output voltage. The advantage of 662k is absence of unwanted signal to great extent and smaller size.



  •  Input Voltage Min: 1.8V
  •  Input Voltage Max: 6V
  •  Output Voltage Nom.: 3.3V
  •  Output Current: 200mA
  •  Dropout Voltage Vdo: 250mV
  •  LDO Regulator Case Style: SOT-23
  •  No. of Pins: 3


Level shifter:

Level Shifter is used to amplify the transmitting or receiving signal to some level. It converts your 3.3v DC signal transmitter by radio chip  to 5v because the peripherals with which it is interfaced operates at 5v .If the signal received is  weak then it converts that signal into desired range.


Circuit Diagram:

LED blinking pattern:

The onboard LED shows the current state of the module.

  • Rapid flash (about 5 times a second): module is on and waiting for a connection or pairing
  • Single quick flash once every 2 seconds – the module has just paired with another device
  • Double quick flash every 2 seconds – connected to another device
  • The HC-05 remembers devices it has paired with and after cycling the power you do not need to re-pair. This means you can go from rapid flash (about 5 times a second) – module is on and waiting for a connection or pairing, to double quick flash every 2 seconds – connected to another device directly.