Description
The circuit below is similar to the one above but can be used with a
laser pointer to toggle the relay rather than a push button. The IR
photo transistor Q1 (Radio Shack 276-145A) or similar is connected to
the set input (pin 6). The photo transistor should be shielded from
direct light so that the voltage at the set input (pin 6) is less than 1
volt under ambient conditions and moves to more than 10 volts when
illuminated by the laser pointer or other light source. The reset time
is about a half second using a 4.7uF cap which prevents the circuit from
toggling more than once during a half second interval. The 10K resistor
and diode provide a faster discharge path for the 4.7uF cap so the
circuit can be retoggled in less than 1 second. The 3K resistor in
series with the photo transistor may need be adjusted for best
performance. The relay shown is a solid state variety to be used with
lights or other resistive loads at less than 3 amps. A mechanical relay
can also be used as shown in circuit above.
Circuit diagram
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