Light Sensor Circuit 2

Light-controlled pond pump
This circuit was constructed to control the pump in a garden
pond, so that it automatically turns on at dawn and off again
at dusk. Not only does this mean that we don’t have to get
cold and wet when turning the pump on or off manually but
it’s also one less job for our kind neighbours when we go
away on holidays!

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Light Detection Using A Phototransistor and Voltage
Comparator
This page describes an example project that turns on a red
LED when light is dim and a green LED when light is bright.
Or more to the point, changes color when objects (such as
a fan blade) pass in front of it.Because the lighting required

to enable either LED is controlled by individual potentiometers,

they can be set such that either, neither, or both LEDs turn on.

That is, the red LED doesn't have to turn on simply because the

green LED turned off.

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Internals of RCX Input Ports and Sensors
When it comes to the active sensors these are much more
complicated inside as can be seen from the figures 4 to 7.
There is however still a simple relationship between the raw
value measured and the sensor resistance if the A/D
conversion takes place with no power is supplied to the

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Laser Pointer Triggered On/Off Switch
Remote control is commonly performed with either modulated
infrared emitters or radio-frequency wireless transmitters.
During a boring presentation, it occurred to me that the
presenter could control a slide show by aiming their laser
pointer at a list of commands with bullet-point targets.
Alternatively, someone lying in bed could set the clock
alarm/snooze (across the room) or turn off lights by simply
aiming the laser dot at the correct spot on the desired object.

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