This simple motion sensor responds to changes
in electric fields. Any person produces some electric charge when moving on isolating
grounds. As soon as someone approaches the sensor, the LED lights for about 10
seconds. You can use it to secure your precious paintings in your private
museum.
To get this 555 cirquit working use a multimeter or an oscilloscope.
You can also use this circuit as an automatic
torch. It lights up when you touch it. If you can´t find it in the dark just
move your shoes a bit on the carpet and such gain some electric charge. This
will trigger the light.
The circuit diagram shows a monostable using
the NE555. 1 MOhm and 10 Microfarad come to a time constant of 10 seconds. The trigger
input is connected to a Darlington made up by
two BC547C. They give enough amplification to sense smallest currents caused by
changes in the electric field.
Sensitivity mainly depends on the size of the
sensor wire. In this case a small wire loop is connected to the Darlington base. But you can also use a longer wire up to
0.5 meters or any isolated metal plate.