Monday, July 14, 2014

Modifying a Bluetooth Headset Device for Personalized Applications

In the previous post we learned regarding the internal circuitry of a typical Bluetooth headset, in this post we'll see how the gadget can be modified or "hacked" in order to make it work for other personalized applications.

In the previous article we learned how to break open a Bluetooth headset device and also investigated the various components enclosed within.

Although most of the stages inside the headset appear to be too sophisticated to digest, the two elements which are still quite traditional are: the speaker and the mic, and those are exactly what we are interested in for implementing the proposed hacking procedures, because these two ports basically become the input and the output terminals of the device.

To be precise it's the speaker outputs that is more useful, which could be assumed to be generating analogue audio frequencies in a push-pull format. This analogue signal can be easily translated and converted into a logical signal for operating a toggling device such as a relay.

In the following couple of images we are able to see the speaker wires which could be simply cut and striped at the ends for accessing the processed analogue frequencies for the required modifications.

Once the above operations are made, it's all about integrating the wires with a bridge network followed by an opto coupler stage, as shown below:

The bridge network converts the differential output response from the Bluetooth speaker outputs into a full wave DC, which is further filtered by the 100uF capacitor to produce a clean DC across the opto input.

The DC is converted into a logical content across the collector/ground of the opto transistor. This output may be configured with any standard flip flop circuit for toggling any desired load.

The above toggling could be initiated by activating the Bluetooth headset with a data from a cell phone or any similar compatible device. Each time the speaker responds, the info gets translated into the above discussed toggling effect over a connected relay.

A flip flop circuit can be seen in the following figure which could be integrated with the above opto output for obtaining the intended relay operations.

Parts List

R3 = 10K,
R4, R5 = 2M2,
R6, R7 = 39K,
R4, R5 = 0.22, DISC,
C6 = 100µF/25V,
D4, D5 = 1N4148,
T1 = BC 547,
IC = 4093,

The above method explains an easy way of hacking a Bluetooth headset for remotely operating a particular appliance, in the next post (yet to be published) we'll learn how to hack a Bluetooth Headset as a wireless home theater system.

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