This device is usually comprised of an LED and a PhotoDiode. A narrow beam of light is shone at a fixed angle to the location where the object to be sensed should be. When the object comes exactly into place the light is reflected back down a short tube within the sensor body onto the photodiode which switches allowing a signal to the next part of the circuit. There are several kinds of batteries available, both rechargeable and non-rechargable. Alkaline batteries flatten this curve somewhat and therefore are best used with motorized equipment.
Rechargeable batteries come in many shapes sizes and chemical groups.
Though they may cost more than three times the price of an alkaline battery, they can easily be recharged from tens to hundreds of times. Ni-Cad are very popular now because they can be made with similar characteristics and packaged the same way as dry cells. For more sustained or heavier loads such as motors Gell cells are very useful. Possibly the largest collection of books on robotics anywhere and with books suitable for all reader levels. Western Canada Robot Games.