Modern wireless headphones help us listen to any sound source without wires. A product that, instead of using the cables to connect to the sound source, uses a wireless technology and a Bluetooth chip that is responsible for sending that signal directly to the headphones.
By the way, although we talk about Bluetooth wireless headphones, there are also infrared wireless headphones. These latest models have a technology similar to that used by the remote controls that we normally use, which also has the advantage of dispensing with the cables although with certain limitations in scope.
However, so that you can create your best wireless headphones, we are going to bet on a much simpler technology with greater reach. To do this, we go to the radio signal. Specifically, a simple VHF transmitter that operates on the band of 87 to 88 megahertz. A frequency zone that is generally not occupied by radio broadcasts, so you will not have problems with interference. Anyway, you can also opt for another band, if necessary.
The VHF circuit
To start working with this particular product, we will need a circuit that follows the principles of a classic VHF emitter or frequency modulation. A simple system consisting of 9 Vdc battery, antenna connection, audio output and the corresponding elements for both the connection and the system setting. Specifically, this adjustment is made by means of the so-called Dip Meter or inductance meter, or by using the adjustment of the CV1 element of the circuit.
As for the antenna branch, it is mounted by means of a central point that makes it more comfortable to connect it to the printed circuit. Something important to prevent damage to the device, in case we have to modify the position of the antenna. Anyway, this antenna consists of a simple piece of copper cable of 1 meter in length, in the way that we can find in other devices such as micro-chains or music equipment.
Varying the frequency
Although we have already talked about the corresponding frequency, we may be interested in varying it in case of interference. Something important if we have powerful radio stations that occupy the frequency band we are talking about, which can affect the reception quality of that sound.
To modify this value, we only have to use a capacitor or an Xtral1 type crystal adjusted to the frequency at which we want to emit this signal. This element has the advantage of giving functionality to the output signal, so that it will serve the approach or the frequency that most interests us at all times.
However, it is also important to keep in mind that any small change or element that can be found in the environment can also generate variations in frequency. This happens, for example, in case we wind up the antenna, that we place it in a certain way or in case we bring some metallic object closer to the device. And it is that the product that we are commenting on does not have any shielding that prevents this type of parasitic conditions in terms of the frequency of emission. Anyway, it is true that if we bet on a crystal in our circuit these risks are reduced.
Device adjustment and resonance
To achieve an adequate resonance of the generated signal, it will be necessary to mount the device in a closed environment and, as far as possible, prevent the loss of this signal. Something especially important in the case of using the crystal systems that we have already mentioned above, since these require good precision to achieve a quality signal.
As a reference, in case we use a chosen crystal of 10,240 MHz, the frequency signal obtained will be the ninth harmonic corresponding to it. In this case, we will have to 10,240 Mhz x 9 = 92.1 Mhz approximately, so that this will be the frequency closest to the reference of the signal obtained. However, with the proper calibration of the CV1 element of the circuit we can comfortably adjust the frequency for maximum accuracy.
As you may have already noticed, this circuit oscillates between the elements determined by the LC set, responsible for generating the output. By altering the construction of the L coil, we can step forward and vary the frequency, in order to achieve maximum accuracy.
Something interesting in areas especially loaded with waves, where finding a clear frequency is complicated, given that it gives us more options to play with greater comfort when determining that frequency. For this reason, it is convenient that all adjustments are made directly in the area where we are going to install the device, to solve such inconveniences.
Final device assembly
We have already referred to the entire interior design of the product but we lack the outer part. And the good news is that we need virtually nothing to proceed with this assembly. So, if we have the necessary knowledge, we can even take care of installing this device inside our TV, leaving the antenna out of it and being careful not to touch what we should not.
The other option is to introduce and mount the elements in any case or box, taking care that everything is closed and well protected, as well as leaving the space open to install the connector. This socket must be properly fixed on the support, in order to avoid problems as we connect and disconnect the device’s output cable.
Once the whole system is assembled, we only have to use an MP3 with radio, the radio function of our mobile or any other similar product to enjoy the audio, with greater coverage even than that offered by Bluetooth.