Entry Sensor Circuit

[extremeads1]

i have an entry sensor circuit as one input block of my microcontroller project so i want to enable the microcontroller to carry out further steps and hence i need to connect it to the input of microcontroller what circuit can i use as the entry sensor circuit ( whenever the object comes infront of the sensor the microcontroller will be enabled and when the object moves away from the sensor the microontroller is disabled ....i wish to imlpement this )..................pls reply and provide a circuit which i can use for this purpose !

 

[HarveyH42]

How much distance from the object to sensor is to be active?
Indoor or outside?

Lighting considerations? Full sun light, mostly shadows?
Artificial lighting? Flourecent, arc, HID

Acoustic considerations?

Don't think you want/need to disable the microcontroller (unless maybe its a PIC ). You can have a loop constantly checking the state of an input pin, or have it trigger an interupt when the pin changes state (good for bringing the MCU out of power saving (SLEEP) mode).

Modulated IR is good for short distance and low light. As reflective, less than 3 feet. Break beam, maybe 20 feet.

PIR is good for around 40 feet, but bright light confuses it.

Ultrasonic... no experience or reading, been kind of expensive to consider in the past.