entry and exit function
1 | photoelectric presense detector |
photoelectric presense detector
o | the heart of this circuit is a "light dependent resistor" (ldr) |
o | the resistance value of this device is over 1 meg when in the dark, and less than 2 k when under bright lighting conditions |
o | the 2.2 k resistor in series with the ldr is inserted to limit the current to a value that will prevent it from overheating |
o | in actual applications, this high current may be experienced if the 555 encounters an internal fault, or when the 100 k resistor is somehow shortcircuited |
o | light is provided from an external source and is assured that the ambient lighting conditions do not neutralize the effect of the light source |