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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. 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. Fig. 1: ...

This battery charger circuit is for Sony Ericsson standard batteries, Li-Polymer type, with a nominal voltage of 3.6V and a capacity of 900mAh. But you can also charge Nokia batteries as well. Charging lithium cells is fairly straightforward. You generate a well regulated voltage and ensure the charging current is sufficiently low so as not to cause overheating problems. Also, when the correct terminal voltage as been attained, it is important to shut down the charging process at that point. The circuit consists of three main sections:   A 5V DC constant voltage supply, which serves as the charging source for the mobile phone battery. Mains voltage is transformed via T1. After rectification and smoothing, via BR1/ C1, about 14V DC is delivered to IC2, which is a 1A 5V regulator. The regulator output delivers the charging current to the mobile phone battery via current limiting resistor R1 and via relay contacts RLA2. Fuse FS1 provides protection in the event of excess current ...