In the relay’s point of view, dark activated means the relay will be activated when the light intensity fall below a certain threshold. Without hysteresis, the relay will be activated and deactivated if the sensed brightness fall under or rise above a single point of darkness level. With hysteresis, the darkness level for activating and deactivating the relay will be different, and this solve the relay oscillation problem when the light intensity is swinging up and down around a single point of no hysteresis activation level.
We can employ the hysteresis of a 555 IC to improve the sensing of a drop in light, since the internal 555 circuit has 1/3 and 2/3 supply voltage thresholds. We have to use a LDR or CDS cell with aout 2 to 8 k resistance at desired light level. At the dark, the resistance of the LDR will rise and activate the relay if the voltage at pin 2 reach 2/3 of supply voltage (8V). After the relay is activated, more light is needed to make the LDR decrease its resistance until the voltage at pin 2 falls below 1/3 supply voltage (4V).
Possibly Related Articles:
- Sound-Activated Lamp (Relay/Switch)
This simple circuit shown int the schematic diagram actives the switch using sound. We can use this circuit for various applications, such as automatic (sound-controlled) disco light or car’s LED... - Touch Switch Activated Relay
This is a simple circuit of Touch switch activated relay. This circuit is used to turn on/off electronic relay using touch sensor. This circuit consist of two main parts, they... - Diac-Triac Phase/Power Control without Hysteresis
Hysteresis in lamp dimmer or in other electric appliance might cause some trouble if you need a fine tuning, something like out of control. This is a circuit of Diac-Triac... - Reduced Hysteresis Diac-Triac Phase/Power Control
This is a Reduced Hysteresis Diac-Triac Phase/Power Control circuit. This circuit is used to control from 5% to 95% of full load power. This circuit can decrease the hysteresis effect... - Sound-Controlled Relay
This is a relay circuit that detect the presence of sound to activate the relay. You can use this sound-controlled relay as voice operated switch, light control, toys, or any... - Alternating Relay Switch
Our reader Andrea (andrea[dot]perugia[-at-]gmail[dot] com) sent his circuit to us, and he creates the circuit for educational intent. The main purpose is to show that you can toggle an output... - LM311 Comparator with Hysteresis
An LM311 comparator circuit with the pin numbers is shown in the schematic diagram figure below. The ground for this transistor is at pin 1 and the open collector output... - Inverting Comparator With Hysteresis
Comparator with hysteresis (Schmidt trigger) can be built using LM339, LM239, LM2901, LM2901V, NCV2901, or MC3302 quad single supply comparator integrated circuit chips. Here is the circuit’s schematic diagram and... - Sound Operated Relay, Control Your Disco Light Automatically By Music Sound
This circuit is not a voice operated switch (VOX) because this circuit is too dumb to differentiate between musical sound or human voice. This is rather a sound activated than... - Overvoltage Protector with Relay
An overvoltage protector circuit is shown in the schematic diagram below. This circuit will work to disconnect the protected device from the power supply when an overvoltage occurs at the... - An Introducton to Relay – Video Tutorial
Below is video which tell us about relay. This video give us an example the use of relay if we want to install an additional electric items in car such... - One Direction Motion Sensor
This is a one direction motion sensor circuit. This motion sensor circuit is used to detects an object passing in one direction, ignoring an object that going to opposite way....
| 
