For micro contollers without the USB Host function you will need a bluetooth module.This includes micro controllers such as the Arduino etc.
Here is an example of a 4-pin Bluetooth serial module front and back:
BEWARE! A couple of gotchas when purchasing a bluetooth module:
1) You can purchase just the module without the ‘backplane’ or ‘interface board’ or sometimes they call it the ‘base board’.
Without this it is smaller and slightly cheaper but there are lots of connections so making it a lot harder to use and there's no flashing light to indicate connection status.
2) You can, if you're not careful, purchase just the backplane or interface board or base board which doesn’t come with the bluetooth module!
A rule of thumb is that these modules cost around 5 uk pounds, 8 us dollars, 6 euros, 7.5 australian dollars. Be suspicious if they are cheaper. Always look very carefully at the pictures. At the time of writing the only place I found to get these modules from were China via eBay.
It says V1.02 on the picture but the ones I got were both V1.05
You may also use other types such as Bluetooth shields etc. And for PCs and Laptops
and the Raspberry Pi you can use an ordinary Bluetooth Dongle or the built-
The above modules are super easy to use as they have just 4 connections and two of those are for power!
So basically there is just TX and RX
(Transmit and Receive)
These always cross over so the Transmit from the module goes to Receive on your device and the Transmit from your device goes to Receive on the module. Easy!
When you apply power to these modules the LED light starts to flash and the module is ready to pair/connect! The default baudrate for these modules is 9600 which is way fast enough for most applications.
See my website and forum at:
For more in-
Ah bluetooth bluetooth bluetooth. It tries its best to imitate a connection over a wire and usually it does a pretty good job but it does have its foibles.
Caveats: You may find that on occasion your BT device is not responding, you may then need to go into BT Settings and ‘unpair’ the device then ‘pair’ with it again. The PIN password for serial BT devices is usually 1234 or 0000 but it can be different and you may need to find out what it is from the makers. Even when paired and connected some serial BT devices may show as ‘paired but not connected’ even while you are sending and receiving to them! Your Android device does not need to be in ‘discoverable’ mode, only your Bluetooth serial device needs to be ‘discovered’.
See the help page on
The general principles with any Bluetooth device is that first you must pair it with your Android device and then once it is paired you can use it with or without specific software.
In pairing the Bluetooth device must first be set to pairing mode.
For some devices like headsets etc. there is usually a multi-
With a Bluetooth serial module as shown above that you are likely to be using with a microprocessor device it can simply be a matter of turning the device on to initiate pairing and connecting mode and this is often indicated by a rapidly flashing LED light.
The next step in the process of pairing with a device is to initiate ‘scan’ mode on your android device (tablet or phone) to scan for devices.
Your Android device will then search for BT devices that are in the vicinity and are in discovery mode and if it finds any it will present you with a list of devices to choose from.
When you choose a device it will then ask you to input the devices PIN code which
is a 4-
When pairing with a PC, Laptop or Raspberry Pi using a Dongle you will make up this pairing ‘password’ yourself and it will need to be entered into both the Android device and the remote device.
Once paired and connected a BT serial device will usually stop flashing its LED light and the light should remain on.
BTInterface attempts to do the pairing and the connecting all at once when you press the discover button but if this fails you may need to go into the Bluetooth Settings and do this manually.
I have a forum at:
Where we can help each other with any problems that you might encounter.
You can also ask for new features and functions etc.