Power MP-3 player RoverMedia Aria-C7 from USB. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Power Supplies

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The pocket multimedia player RoverMedia Aria-C7 (Fig. 1) plays audio files in MP3, WMA, WAV formats, is equipped with the functions of a voice recorder and a VHF stereo radio receiver with the ability to record radio broadcasts. Its weight is 25 g, dimensions are 92x29x30 mm, and it is powered by one galvanic cell or AAA battery. During the operation of this player, it turned out that it consumes the energy of the power source relatively quickly. Measurements showed that at a supply voltage of 1,5 V, the current consumption, depending on the operating mode, is 30 ... 100 mA. This is a lot for a compact device with a relatively small battery.

Fig. 1

In order to reduce the consumption of chemical current sources operated in conjunction with this player, it was decided to "teach" it to be powered not only from the battery installed in it, but also from the USB port to which it can be connected. The fact is that if you first remove the battery and connect the player to the USB connector of the computer (or charger), the screen backlight turns on, but after a few seconds it displays information about the absence of the power supply. In such a situation, only communication with the computer is possible, and other functions are blocked.

Fig. 2

An analysis of the player circuit showed that the negative terminal of the built-in USB connector is connected to the negative terminal of the battery and the common wire of the stereo phone jack. This greatly simplifies the modification of the device in accordance with the scheme shown in Fig. 2. The numbering of the elements is conditional, and the designations of the newly introduced elements begin with the number 1. A parametric voltage regulator is assembled on the 1VT1 transistor, 1R1, 1R2 resistors, 1VD2 zener diode and 1VD1 diode, which simulates the presence of a galvanic cell or battery in the power compartment. The output voltage of the stabilizer is 1,4 ... 1,8 V, it depends on the stabilization voltage of the zener diode 1VD2. Schottky diode 1VD1 reduces the output voltage of the stabilizer. Resistor 1R2 - protective.

If you install a Ni-Cd or Ni-MH battery in the power compartment of the player, after applying +1 V to the XP5 USB connector, it will start charging. If there is a fresh salt electrochemical cell in the battery compartment, a current of about 2 mA will flow into it.

If an alkaline galvanic cell is used, it must be removed before connecting the player to an external voltage source.

Fig. 3

On fig. 3 shows how additional parts can be placed. Diode 1VD1 (can be replaced by 1N5818, 1N5819, SB120) is installed near the socket for connecting stereo phones and soldered by the cathode to the positive contact of the battery holder. The 1VT1 transistor is glued with Queen-Tol glue to the printed circuit board next to the microphone. The zener diode 1VD2 (TZMC-2V4 is suitable) is soldered with the cathode output to the 1VT1 base output, and the anode output to the common wire - to a wide strip of foil nearby. Resistors 1R1 and 1R2 are installed near the USB connector. The connections are made with a thin stranded mounting wire, for example MGTF-0,03. Thin plastic tubes were used to isolate the rations and parts, which were fixed with a zaponlak. Soldering was performed with a 6.15 W low-voltage soldering iron with a sharp tip.

The player has two quartz resonators, which are held only on their own conclusions. To exclude the possibility of their breakage, each resonator must be fixed on the printed circuit board with a drop of glue.

During the operation of this player, it turned out that the miniature control buttons begin to work unstable after a while, especially if the player was operated without a waterproof cover in the pockets of outerwear. The malfunction looks like the execution of random commands by the player and is due to a significant increase in the resistance of closed contacts. If there are no suitable buttons for replacement, you can try to restore the regular ones. To do this, a drop of 96% ethyl alcohol is introduced into the problem button, after which it must be pressed intensively for 2.3 minutes. The procedure is repeated three times, and then the player is dried for two hours at a temperature of 40.45 °C. Using the method described above, the author managed to reduce the resistance of the closed contacts of the buttons from 10 ... 200 kOhm to several ohms.

Author: A. Butov

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