Peripherals

• Keyboard & mouse

  • Keyboard can be wired (USB) or wireless (2.4Ghz ISM), detects key presses and transmits characters by ASCII codes.

  • Mouse primarily transmits x,y coords and left/right click.

• Capacitive Touch Interface

  • Touch screen works cause of change in capciitance of the hardware in presence of finger. This change in cap is affected by dielectric of the capacitor.

• Camera

  • Consists of Lens, Image sensors (convert photons to electric signals, then ADC converion for processing), Image signal processor (ISP; auto focus, exposure etc.), Interface I/O (reformatting for delivery to host processor).

• Microphones

  • Use variation in capacitance when diaphragm is displaced by sound pressure to transduce sound wave to electric signals.

  • Transduced signal is analog, but ADC can convert it to digital.

  • ECM microphone: the charges are stored permanently on the electret.

  • MEMs microphone: electrical charges provided by charge pump.

• Liquid Crystal Display (LCD)

  • Liquid crystal molecules twist the light and controls the amount of light passing through the colour filters.

  • The orientation of these molecules controlled by electric field.

• Speaker

  • Electromagnetic coil moves a speaker cone, mechanical energy converted to sound.