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Twilight switch
Twilight switch automatically switches on and
off the lighting of your home, garden or other
place. When it gets dark, the device switches on
the output relay. The twilight switch is equipped
with circuitry that eliminates the possibility of
oscillation if the illumination level is at the
operating threshold.
Specifications
• photo resistor as a light sensor
lighting is at the operating threshold
• power supply: 12-15V DC
• hysteresis eliminates oscillations when the
• adjustable sensitivity
• active status indication with LED
• output relay with contacts 230V AC, 8A
Schematic of the twilight switch is shown in
Figure 1. It is based on the TL071 operating
amplifier working as a comparator. The TL071
compares the voltage from the potentiometer
PR1 to the voltage from a resistive divider made
up of a resistor R3 and a photoresistor. The
decrease in the intensity of light incident on the
photoresistor causes an increase in the voltage
on the pin 2 of the operational amplifier U1. If
the voltage on the pin 2 will be higher than the
voltage on the pin 3, the amplifier output
voltage appears, causing conduction of the
transistor T1 and switching on the relay RL1.
The PR1 potentiometer allows for adjusting the
sensitivity threshold over a wide range. The C3
capacitor eliminates the possibility of oscillation
if the illumination level is at the operating
threshold. Relay contacts are switched on at
dusk and off at dawn. Using the changeover
contacts can reverse the operation of the
device. The high load capacity of the relay
contacts enables the switch to be used in a
variety of applications. The switch can be
powered by 12V DC from any AC adapter or a
battery.
DIFFICULTY
LEVEL
Functional description
AVT 1460
Twilight switch
http://bit.ly/2JYmoFM
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