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May 13, 2023

How to Configure Arduino with HC-05 (ZS-040) Bluetooth Module in AT Mode

In this tutorial, we will learn how to use the HC-05 (ZS-040) Bluetooth module with Arduino to communicate wirelessly with other devices. The HC-05 module is a popular and low-cost Bluetooth device that can operate in two modes: data mode and AT mode. Data mode is the default mode, where the module acts as a serial bridge between the Arduino and another Bluetooth device. AT mode is a special mode, where the module can receive commands to change its settings, such as the name, password, baud rate, etc.

To enter AT mode, we need to connect the HC-05 module to the Arduino in a specific way and send some commands through the serial monitor. In this tutorial, we will use a breadboard, some jumper wires, a 5V power supply, and a voltage divider circuit to connect the HC-05 module to the Arduino. We will also use the SoftwareSerial library to create a virtual serial port for the module.

Arduino with HC-05 (ZS-040) Bluetooth module – AT MODE

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Step 1: Connect the HC-05 Module to the Arduino

The HC-05 module has four pins: VCC, GND, TXD, and RXD. VCC and GND are used to power the module with 5V. TXD and RXD are used to transmit and receive data between the module and the Arduino. However, there is a problem: the HC-05 module uses 3.3V logic levels for its TXD and RXD pins, while the Arduino uses 5V logic levels for its digital pins. This means that we cannot directly connect the TXD pin of the module to the RX pin of the Arduino, or vice versa, because it may damage the module or the Arduino.

To solve this problem, we need to use a voltage divider circuit to lower the voltage from 5V to 3.3V on the TX pin of the Arduino. A voltage divider circuit consists of two resistors connected in series between two voltage sources. The output voltage is taken from the junction of the two resistors. The formula for calculating the output voltage is:

In our case, we want Vout to be 3.3V and Vin to be 5V. We can use any two resistors that satisfy this equation, but a common choice is to use a 1kÎ resistor for R1 and a 2kÎ resistor for R2. This gives us:

This is close enough to 3.3V for our purpose.

Now that we have our voltage divider circuit ready, we can connect it to the TX pin of the Arduino and the RXD pin of the HC-05 module. We also need to connect the RX pin of the Arduino to the TXD pin of the HC-05 module directly, since we don't need to lower the voltage from 3.3V to 5V. Finally, we need to connect the VCC and GND pins of the HC-05 module to a 5V power supply.

The following diagram shows how to connect everything on a breadboard:

Note that we are using pins 10 and 11 on the Arduino as our virtual serial port for the HC-05 module. You can use any other two pins that support SoftwareSerial, but make sure to change them in your code accordingly.