Mobile Car Stereo Player

Using a mobile phone while driving is dangerous. It is also against the law. However, you can use your mobile phone as a powerful music player with the help of a stereo power amplifier. This does away with the need of a sophisticated in-dash car music system. Most mobile phones have a music player that offers a number of features including preset/manual sound equalisers. They have standard 3.5mm stereo sockets that allow music to be played through standard stereo headphones/sound amplifiers. Nokia 2700 classic is an example.

Mobile Car Stereo Player Circuit Diagram

A car audio amplifier with 3.5mm socket can be designed and simply connected to the mobile phone output via a shielded cable with suitable connectors/jacks (readymade 3.5mm male-to-male connector cable is a good alternative). Fig. 1 shows the circuit of car stereo player. It is built around popular single-chip audio power amplifier TDA1554Q (IC1). The TDA1554Q is an integrated class-B power amplifier in a 17-lead single-in-line (SIL) plastic power package.

IC TDA1554Q contains four 11W identical amplifiers with differential input stages (two inverting and two non-inverting) and can be used for single-ended or bridge applications. The gain of each amplifier is fixed at 20 dB. Here it is configured as two 22W stereo bridge amplifiers. The amplifier is powered from the 12V car battery through RCA socket J2. Diode D1 protects against wrong-polarity connection. LED1 indicates the power status.

Stereo Jack :

(a) 3.5mm stereo socket and (b) 3.5mm Stereo Jack

Connect stereo sound signal from the 3.5mm headset socket of the mobile phone to audio input socket J1. When you play the music from your mobile, IC1 amplifies the input. The output of IC1 is fed to speakers LS1 and LS2 fitted at a suitable place in your car. Electrolytic capacitor C5 connected between pin 4 of IC1 and GND improves the supply-voltage ripple rejection. Components R2 and C4 connected at mute/standby pin (pin 14) of IC1 eliminate the switch on/off plop. The circuit is quite compact. A good-quality heat-sink assembly is crucial for IC1. Fig. 2 shows the stereo socket and stereo jack.

Proposed enclosure

Assemble the circuit on a general-purpose PCB and enclose in a suitable cabinet. Small dimensions of the power amplifier make it suitable for being enclosed in a plastic (ABS) case with vent holes. Signal input socket, speaker output terminals, on/off switch, indicator, fuse holder and power supply socket are best located on the front panel of the enclosure as shown in Fig. 3.

Source : http://www.ecircuitslab.com/2012/04/mobile-car-stereo-player.html

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Test Beeper For Your Stereo

The test beeper generates a sinusoidal signal with a frequency of 1,000 Hz, a common test  frequency for audio amplifiers.  It consists of a classical Wien- Bridge oscillator (also known as  a Wien-Robinson oscillator). The network that determines the  frequency consists here of a series connection of a resistor and  capacitor (R1/C1) and a parallel connection (R2/C2), where  the values of the resistors and  capacitors  are  equal  to  each  other. This network behaves, at  the oscillator frequency (1 kHz  in this case), as two pure resistors. The opamp (IC1) ensures  that the attenuation of the net- work  (3  times)  is  compensated  for.  In  principle  a  gain  of  3 times should have been sufficient to sustain the oscillation,  but  that  is  in  theory.  Because  of tolerances in the values, the  amplification needs to be (automatically) adjusted.

Circuit diagram:

Test Beeper For Your Stereo circuit Diagram

Instead of an intelligent amplitude  controller  we  chose  for  a  somewhat simpler solution. With  P1, R3 and R4 you can adjust  the gain to the point that oscillation takes place. The range of P1 (±10%) is large enough the cover the tolerance range. To sustain  the oscillation, a gain of slightly  more than 3 times is required,  which  would,  however,  cause  the amplifier to clip (the ‘round-trip’ signal becomes increasingly  larger, after all). To prevent this  from happening, a resistor in se-ries with two anti-parallel diodes  (D1 and D2) are connected in  parallel  with  the  feedback  (P1  and R3). If the voltage increases to the point that the threshold  voltage of the diodes is exceed-ed, then these will slowly start to  conduct.

The consequence of this  is that the total resistance of the  feedback  is  reduced  and  with  that  also  the  amplitude  of  the  signal. So D1 and D2 provide a  stabilising function. The distortion of this simple oscillator, after adjustment of P1 and  an output voltage of 100 mV (P2  to  maximum)  is  around  0,1%.  You can adjust the amplitude of  the output signal with P2 as required for the application. The  circuit is powered from a 9-V battery. Because of the low current  consumption  of  only  2 mA  the  circuit will provide many hours  of service.

Author :Ton Giesberts  - Copyright : Elektor Electronics

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Quality Stereo Wireless Microphone or Audio Link

This stereo FM wireless microphone also makes a great quality audio link. We tested it to beyond 50 meters and it was rock solid. It’s certainly not the first wireless microphone we’ve ever published but this one is a little different. It’s stereo, providing surprisingly good quality sound. Second, it has a really good range. We tested it at well over 50m and it was still performing very well – noise-free, in fact – but at the time we couldn’t get our receiver any further away. So it’s likely to have even better range than that.

Complete Project:

Its easy to build, requires very little setup... and its cheap! In fact, the low price might turn some people off, thinking its low quality. Try it - and be pleasantly surprised!

Third, it really is simple to build – the hard work (the transmitter module) is already done for you. It’s just a matter of assembling the microphone module, which contains the electret mics themselves, preamp and level controls, and soldering the transmitter module onto it, "piggy back" style.

FM Transmitter:

Finally, the transmitter module is crystal-locked, so you won’t have the drift probles of some earlier wireless microphones. And just in case you were wondering, that doesn’t mean the output is locked to one particular frequency – it has a nifty synthesis circuit built in to give you the choice of seven different frequencies between 106.7MHz and 107.7MHz.

On-board preset pots adjust the sensitivity of each channel to take into account mic differences or if you require different levels in each channel.

By the way, the transmitter module is quite capable of operating at line level if you want just a line level transmitter (eg, to feed an audio program around your home). Sensitivity is about 100mV. Oatley Electronics, who designed the kit, have the transmitter module available by itself if that’s what you’re after. But more on that anon.

Parts Layout:

You also have the choice of two power supply levels – 3-6V or 7-15V DC. The latter results in a lower current drain. The transmitter module also has a "5V out" rail to supply power to the preamp module.

Circuit Diagram:

Two electret microphone inserts are supplied in the kit. These can be soldered direct to the PC board to make it a fully self-contained project or they can be attached to the board via suitable lengths of mini shielded coax cable. A third option is to use "proper" microphones – they can be electret or dynamic types – but no provision has been made for plugging these in.

Typical Specifications: 
 
Audio response:.....................20Hz-15kHz.
Channel separation: ........................40dB
Total Harmonic Distortion: ...............0.1%
Output Frequency:...........106.7-107.2MHz
Pre Emphasis: ..................................50μS
DC supply voltage range: ................3-15V
Supply Current: .......................30mA @ 9V

Source: http://www.ecircuitslab.com/2011/06/quality-stereo-wireless-microphone-or.html

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