Arduino to Arduino by Bluetooth

Updated 12.06.2016: Added example 2

In the Connecting 2 Arduinos by Bluetooth using a HC-05 and a HC-06: Pair, Bind, and Link post I explained how to connect a HC-05 to a HC-06 so that when powered they automatically made a connection. Here we look at using that connection to get Arduinos talking over Bluetooth. Before continuing you need to have the Arduinos and BT modules set up as per the previous post. Here I am using 2 HC-05s. One in master mode the other in slave mode. The setup process for the slave mode HC-05 is the same as the HC-06 in the previous post.

Arduino2ArdionoBT_Breadboards_01_1600

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HC-05 fs-040 State Pin

This post follows on from Arduino With HC-05 Bluetooth Module in Slave Mode

The STATE pin on the HC-05 zs050 board is connected to the LED 2 pin on the small bluetooth module and the LED 2 pin is used to indicate when there is an active connection. This means the Arduino can connect to the STATE pin and determine when we have a connection. The STATE pin is LOW when the HC-05 is not connected and HIGH when the HC-05 is connected.

As a quick visual indicator you can put a LED + suitable resistor on the STATE pin. When the module is connected the LED will light.

You can also use the Arduino to read the value of the STATE pin.

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Connecting 2 Arduinos by Bluetooth using a HC-05 and a HC-06: Pair, Bind, and Link

In a previous post I showed how the HC-05 can auto connect to other Bluetooth devices by setting the HC-05 to pair with any device using CMODE=1. This is quick and easy but does not give any control over which other device the HC-05 connects to.

In this post I show how to set up the HC-05 to always connect to the same HC-06. For this we use PAIR, BIND, and LINK.

I am using 2 separate Arduino IDEs; version 1.6.3 which is installed, and version 1.0.5 which I run from a folder (it is the non install version). This allows me to use 2 IDEs at the same time, each connected to a different Arduino. It also gives me 2 serial monitors, one for each Arduino.

The modules used are the zs-040 versions of the HC-05 and the HC-06.

The HC-05 has 2 AT modes which I refer to as “mini” AT mode and “full” AT mode and some commands only work when in “full” AT mode. To enter “full” AT mode pin 34 needs to be HIGH and kept HIGH. To accomplish this I have made a connection from pin 34 to +3.3v. See the diagram below (or after the jump).

If you are not sure about the different AT modes take a look at Arduino with HC-05 (ZS-040) Bluetooth module – AT MODE

If you are not familiar with how the HC-06 and HC-05 work it may be worth while checking out some of the other posts:
HC-05 and HC-06 zs-040 Bluetooth modules
Arduino and HC-06 (ZS-040)
Arduino With HC-05 Bluetooth Module in Slave Mode
Connecting 2 Arduinos by Bluetooth using a HC-05 and a HC-06: Easy Method Using CMODE

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Connecting 2 Arduinos by Bluetooth using a HC-05 and a HC-06: Easy Method Using CMODE

Making a connection Between a HC-05 and a HC-06: Method 1

Using the CMODE command we have an easy way to connect the HC-05 and the HC-06. When the HC-O5 is configured to pair with any address (AT+CMODE=1) it should connect to a HC-06 automatically. No binding etc is required.

I am using the zs-040 modules and other modules should be the same. If you have issues check the data sheet for your modules.

The Set Up

I am using 2 different Arduino IDEs; version 1.0.5 and version 1.6.3 but this not required. You can run 2 instances of the same IDE which then allows yo to have 2 serial monitor open at the same time.

The Arduino connected to the HC-05 is on COM8 and the Arduino using the HC-06 is on COM17

ARD2ARD_SETUP_IDE

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

Updated 19.07.2015
Updated 26.07.2015
Updated 30.10.2015

Update 2016-08-01
The zs-040 breakout boards are now being used for many different modules and you may not have the exact same boards as those shown below. Recently I received some new zs-040 HC06s and HC-05s that have a slightly different daughter board and a very different firmware. On the new HC-05s pin34 has to be pulled HIGH before connecting power to enter AT mode. Bringing pin 34 HIGH after powering the modules has no effect.

 
 

AT mode allows you to interrogate the BT module and to change some of the settings; things like the name, the baud rate, whether or not it operates in slave mode or master mode. When used as a master device AT commands allow you to connect to other Bluetooth slave devices.

There are many slightly different HC-05 modules, the modules I have are marked ZS-040 and have an EN pin rather than a KEY pin. They also have a small button switch just above the EN pin. They are based on the EGBT-045MS Bluetooth module.

Update: I now also have boards marked fc-114. See:
HC-05 FC-114 and HC-06 FC-114. First Look
HC-05 FC-114 and HC-06 FC-114. Part 2 – Basic AT commands
HC-05 FC-114 and HC-06 FC-114. Part 3 – Master Mode and Auto Connect

On the zs-040 modules there are 2 AT modes. I do not know if this is intentional but some commands only work when pin34 is HIGH. Other commands work when pin 34 is either HIGH or LOW. This fooled me for quite a while. For this post I have called the different modes “mini” AT mode and “full” AT mode.

HC-05 zs-040

To activate AT mode on the HC-05 zs-040 modules we can:
– 1. Hold the small button switch closed while powering on the module.
– 2. Set pin 34 HIGH (3.3v) when power on.
– 3. Close the small push button switch after the HC-05 is powered.
– 4. Pull pin 34 HIGH after powering the HC-05.

Method 1.
Enters AT mode with the built in AT mode baud rate of 38400. The baud rate cannot be changed by the user.
This method allows the module to enter AT mode on start but but does not keep pin 34 HIGH and uses the “mini” AT mode.

Method 2.
Enters AT mode with the built in AT mode baud rate of 38400. The baud rate cannot be changed by the user.
If you keep pin 34 HIGH you will enable the “full” AT mode which allows all AT commands to be used.
If you let pin 34 return LOW after power on then “mini” AT mode will be enabled.

Method 3.*
Enters “mini” AT mode using the user defined communication mode baud rate.

Method 4.*
Enters “full” AT mode using the user defined communication mode baud rate.

If pin 34 is kept HIGH then the HC-05 enters the “full” AT mode. If pin 34 is brought HIGH and returned to LOW it will put the module in to “mini” AT mode.

* added 21.07.2015

Method 1 and 2 are good in that you know the baud rate – it will always be 38400. This could be useful if you have modules other people have used or if you forget what communication mode baud rate you have previously set.

Method 3 and 4 adds convenience. You can enter AT mode, make changes and return back to communication mode without switching sketches and messing around with different baud rates.

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Arduino With HC-05 Bluetooth Module in Slave Mode

Arduino and HC-05 in communication mode

Updated on 18.07.2015.

Updated 01.12.2016
There are now newer HC-06s and HC-05s that use the zs-040 breakout boards. These new modules have a LED (usually blue) at the top left of the Bluetooth daughter board and have a different firmware to the below. See HC-06 hc01.comV2.0 for an introduction to the HC-06. I haven’t written up details on the HC-05 yet.

 
 
Here is the zs-040 version of the popular HC-05. The HC-05 is based on the EGBT-045MS Bluetooth module. It can operate as either a slave device or a master device. As a slave it can only accept connections. As a master it can initiate a connection.

HC-05 zs-040

The EGBT-045MS Bluetooth modules (the smaller daughter board) is a 3.3v device. The HC-05 break out board has a 3.3v regulator that allows an input voltage of 3.6v to 6v but the TX and RX pins are still 3.3v. This means you can use the 5V out from the Arduino to power the boards but you cannot connect the Arduino directly to the HC-05 RX pin.

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.

As a quick guide to the voltage divider; 1K + 2K = 3K. 1K is a third of 3K so it reduces the voltage by a third.
One third of 5V is 1.66 and 5-1.66 = 3.33 which is what we want. Putting the resistors the other way would reduce the voltage by 2 thirds.
For more information on voltage dividers have a look at the Sparkfun tutorial

Since the Arduino will accept 3.3 volts as HIGH you can connect the HC-05 TX pin (data out) directly to the Arduino RX pin (The 5V Arduino takes a voltage of 3V or more as HIGH).

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HC-05 and HC-06 zs-040 Bluetooth modules. First Look

Update: If you have modules that have a blue LED in the top left hand corner then you have a newer model with a slightly different firmware although they should operate the same.

I recently bought some HC05s and HC-06 Bluetooth modules. These are pretty standard, especially when using with the Arduino and I was surprised at how easy it was to get basic serial communication working. There are several slightly different modules available. The ones I have are marked zs-040. The zs-040 boards differ from some of the other modules in that they have a EN pin rather than a KEY pin.

HC-05 & HC-06 - ZS-040
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