Simple Circuit based 2N2222: enabled swicth day or night

Today we have two simple circuit is a transistor switch at the base of the transistor with a voltage divider. The first is the 100K Potentiometer 1K more resistance protection.Deuxièmement layer, the resistance of LDR. This is the schematic representation of the circuit:

When the light changes on the surface of the LDR, LDR is the resistance. The more light, the greater the resistance of the LDR, the less friction, plus the tension of it. The less light, more resistance and therefore the higher the voltage at its terminals.
Electronic components list:
D1 = 1N914
Q1 = 2N2222 NPN transistor similar OR Q1 = 2N2222 or similar NPN transistor
R1 = R1 = Photoresistor photoresistor
Variable Resistor R2 = 50K R2 = 50K variable resistor
R3 = R3 = 1K 1K
Relay = 5 to 6 volt relay. Relay = 5 to 6 volts relay.


When the voltage increases, the SD of the transistor 2N2222 and thus the ice increases accordingly, until the current is sufficient to activate the relay.

The amount of light that can be changed to activate the relay by a change in the 100k pot. any change in the knob to the voltage drop effects LDR because they are both members of the voltage divider described above.

The 1N4001 diode is used to relieve stress again, if the relay is deactivated. It is very important to the diode, as can be infringed without the transistor.
Before serving the work to the extent of activation. It does not detect a problem, light or dark or operate the relay, but it will be a problem if the relays are released. At this point, the circuit has a large hysteresis. Therefore, we must continue to strengthen the signal before we apply to the switching transistor.

We BC517 NPN Darlington transistor pair. Should we 2N2222 between him and the LDR, as shown in the following circuit:

This addition increases the sensitivity of the circuit. The window of hysteresis is dramatically reduced, but there is still an area known as the relay is activated, it will not be rotated by the same amount of light that existed just prior to activation.
Only one adjustment and (of course) potentiometer. Your goal is to operate the circuit when the relay is equal to or less light to the preset value. The best way to do is:

The LDR for the amount of light you light. Hold the knob in the greatest value. Then start slowly turning the potentiometer and reduce drag. If you "click" of the relay listens to find your reference. From that moment on, whenever the light is less than or equal to (or more if the circuit is turned on the light "depending on configuration) is in the light you created this preference is enabled, the relay.