Most commonly the emitters and sensors are positioned within the perimeter, mounted on a small PCB. The light is directed back and forth of the keyboard inside and it could only be blocked by the actuated keys. Most optical keyboards require no less than 2 beams (mostly vertical beam and horizontal beam) to determine the actuated key. Some optical keyboards use a special key structure that blocks the light in a sure sample, permitting just one beam per row of keys (most commonly horizontal beam).
Smaller external keyboards have been introduced for devices without a constructed-in keyboard, such as PDAs, and smartphones. Small keyboards are also useful the place there is a restricted workspace. In normal usage, the keyboard is used as a text entry interface for typing textual content, numbers, and symbols into software software corresponding to a word processor, internet browser or social media app.