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
Designing The Low-Cost Mobile PC - schematic

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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