Designing The Low-Cost Mobile PC

  
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A standard 12-volt auto electrical system can be considered to be a powerful but unreliable source of low-voltage DC current. Some of the features any mobile PC installation should provide include: Automotive systems must be designed to strict electrical standards. Your car`s starter motor, along with many of its accessories, are high-current loads that are inductive in nature. Cranking and accessory

operation can induce large spikes that can upset or destroy any sensitive equipment left unprotected. Newer cars with lots of engine control and diagnostic hardware are much better-behaved than older cars in EMI/RFI terms, but it still makes sense to anticipate the worst in your power-supply design. For most of us, that means using an off-the-shelf power supply solution, rather than rolling our own from scratch. Either an inexpensive 300-watt inverter or commercial 12-volt ATX supply should address these concerns. It`s possible to turn your mobile PC on and off manually with a conventional power switch, but that`s not what you want. Your stereo doesn`t work this way - it comes on when you turn the key, and shuts off when you kill the ignition. You want your computer to do the same. Unfortunately, unlike the older AT-style PC motherboards, many newer ATX-style boards don`t turn on automatically upon application of power. (Check your CMOS setup options - some BIOS versions do support this. ) An ATX power switch can`t be simply hard-wired to the "on" position; the motherboard requires a momentary-contact pulse to turn the system on, so some additional circuitry is likely to be necessary. Almost without exception, the first car CD players on the market had a very annoying drawback compared to the cassette-tape players they were hoping to replace. Every time you started your car, your CD would restart play from the beginning of...



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