| 摘要 |
An overhead projector comprises a housing having an upwardly facing writing plate and a Fresnel lens below the writing plate. A hollow support arm extending up from one side of the housing supports a projection head comprising a lamp directing light down onto the writing plate, a variable objective lens receiving an image from the writing plate and a deflection mirror for directing the image onto a projection screen. A power supply in the support arm supplies power for the projector including the lamp and a blower in the support arm for cooling the power supply and lamp. A microprocessor in the support arm has inputs receiving signals from sensors for sensing the distance from the projector to the screen, ambient brightness, brightness contrast in the projected image on the screen and the temperature of the power supply and the microprocessor. The microprocessor has outputs for regulating the focus of the objective lens, the speed of the blower, the brightness of the lamp and the voltage of the power supply.
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