The main function of the proposed system is to turn on the light (or other electrical load) at the time of reduction of light below a certain threshold. This is a typical dimmer switch, with one exception: this type of system usually turn off the light at dawn, and the proposed the system has a built-in timer management deactivate the device after a certain period of time.
Typical applications of the proposed device can be or garden lighting lighting outbuildings. After dark the light comes on on and off, depending on the programming of the device using 2, 4,6, 8 or 12 hours. The device has built-in protection system short-term illumination in front of a premature restart.
Regardless of the function the twilight of the switch, the device can also works as a regular timer, start with pulse or logical level, to turn the light on or connect a different load.
In addition, the timer has advanced a very interesting feature - detection the time of passage of the voltage through zero and turning on the triac at this point. It removes the necessity to use a variety of filters to suppress interference.
The figure shows a diagram of a twilight switch.
Technical parameters
- The load capacity, W......1000
- The voltage NT, ......3 5...
- Current consumption NT, mA......25-50
- Maximum control current of the triac, mA......7
Device built according to the standard scheme based on IC T, which is fed from a network voltage 220 through the diode D1. The voltage level is set using the divider resistors R6 and R7, Zener diode D2 maintains a stable voltage.
Triac Q1 is controlled by short pulses from the output of TRIAC IC1. Synchronization with network and defining a passage through zero provides a resistor R5, which connected to input ZC (Zero Crossing).
The timer can be started in three ways.
1. When the voltage at pin CDS level below half the voltage power. This condition may occur when the resistance of the photoresistor, reduced lighting, increased to 220 ohms. This state should last about 1 minute eliminating possible interference and prevent the execution the timer in the case of short-term changes of light level. Should notice that the value of the resistor R3 should be selected depending on the type used in the device of the photoresistor.
2. When applying to the input of ONESHOT negative pulse of more than 60 msec.
3. When applying a low log. level to the input LEVEL
The time when the timer is set using jumper JP1.
The permissible load depends on the type triac and availability good cooling.
Author: A. ARP