Automatic light/dark activated systems have very common utilities in day to day life. For example, street lighting at night, morning alarm, automatic emergency [[wysiwyg_imageupload::]]light, dark activated buzzers and so on. The project explained here can be used in several such systems. This circuit has a sensor component which works in response to the ambient light condition. The output of this sensor is compared with a set reference value and whenever the light condition changes from dark to light or light to dark, the output goes high. In this project, the surrounding illumination is observed by a light dependent resistor (LDR) which acts as a sensor for the circuit. The voltage drop across this LDR corresponds to a particular intensity of light. Read on more to find out how the circuit is made and how it works.
Ever imagined how the street lights would turn on automatically in the evening and go off in the morning? Is there anyone who comes early morning to turn off [[wysiwyg_imageupload::]]these lights? The following circuit based project can perform this job properly. In this circuit, the output pin of the comparator goes high depending on the configuration of LDR so that it can be made light or dark activated. This output is connected to a transistor T1 (BC 547) which acts as a switch for the relay. This circuit uses the output from a simple light/dark activated circuit and drives a relay in its output which can be further coupled to switch on/off an electrical appliance in a household. An appliance can be made dark or light activated by slightly changing the circuit’s configuration. This idea finds numerous applications such as, automatic watering of gardens at evening, automatic night lamp, dark activated siren and so on. Read on more to find out how the circuit is made and how it works.
At times we forget to switch off our heating devices and eventually they get damaged. Therefore there is always a need of a device which can alert by sounding [[wysiwyg_imageupload::]]an alarm if the device temperature goes beyond a particular value. Same concept can be used in this project about fire alarm. If a building catches fire then it will raise an alarm and people could evacuate the building. This circuit uses a LM35 temperature sensor along with a LM339 comparator. Interfaced to LM339 are the following components: Resistors, Capacitors, Transistors, 555 Timer, Buzzer (output). This project about fire alarm circuit is based around LM35 which is a temperature sensor and could be used to switch an alarm when temperature goes beyond a preset value. In this circuit the output of LM35 is fed to the negative pin of comparator of LM339. The positive input is connected to a preset VR1 of value 10K.