A few light sensor circuit based projects can be listed as a solar highway lighting system with auto turn off in daytime, security alarm system by photo electric sensor, sunset to sunrise lighting switch, Arduino managed high sensitive LDR based power saver for street light control system, etc,. A Better Light Sensor Switch (PCB Included): Some time ago I was asked by my father to design a light sensor circuit for him, he has some LED's installed and a solar panel and a battery array, which he then uses to power his garden lights. Cart Total:  As the name suggests, a comparator will take a voltage at the input and compare it with another, depending if it's higher or lower the output will become high or low, depending on the configuration. Then, we apply the above circuit to make the automatic Air pump. The variable voltage is the voltage coming from the sensor, more light means more voltage, and less light means less voltage in this case, this voltage variation be achieved thanks to a voltage divider consisting of the LDR and a resistor. OP amps have a very high impedance, this means almost no current makes it though the input pins, this allows us to design the voltage divider without taking into account any loads. The circuit of Light Sensor Switch Circuit is shown in figure 1 and is built around very popular operational amplifier IC, light dependent resistor (LDR), a general purpose PNP transistor and few other components like resistor, relay etc. Check LightinTheBox for more products. switch and hence any AC and DC appliance connected with the relay will become activated. I also used some connectors to connect the hysteresis resistor, in case I want to change it afterwards. The function of this light sensor was to turn on the LEDs at night when the light falls under certain threshold, that was quite straight forward, and I built a simple comparator to do the job. Share it with us! January 16, 2011 . The switch is a semiconductor relay S202DS2 and the oscillator is 4060. Proceed to Checkout. You can now login using your Facebook or Google account. The transistor is used to switch on some LEDs (or other source of light) when the light level drops below a certain threshold. 4 years ago. 10k to 100k resistor (to be used with LDR in a voltage divider). I used a copper clad board to create the circuit using the toner transfer method. Once the voltage coming from the voltage divider is lower than the reference voltage the lights will turn on, but since the output is connected to the reference voltage by a resistor, the reference voltage will rise a bit as the output voltage goes high, once this happens, the variable voltage will have to climb that gap that has been just created to turn the output low again. Since we have 12V CT 12V or 24VCT transformer so set this circuit form. AF+93AL+355DZ+213AS+1684AD+376AO+244AI+1264AG+1268AR+54AM+374AW+297AU+61AT+43AZ+994BS+1242BH+973BD+880BB+1246BY+375BE+32BZ+501BJ+229BM+1441BT+975BO+591BA+387BW+267BR+55IO+246BN+673BG+359BF+226BI+257KH+855CM+237CA+1CV+238KY+1345CF+236TD+235CL+56CN+86CX+61CC+61CO+57KM+269CG+242CK+682CR+506CI+225HR+385CU+53CY+357CZ+420DK+45DJ+253DM+1767DO+1809TP+670EC+593EG+20SV+503GQ+240ER+291EE+372ET+251FK+500FO+298FJ+679FI+358FR+33GF+594PF+689TF+GA+241GM+220GE+995DE+49GH+233GI+350GR+30GL+299GD+1473GP+590GU+1671GT+502GN+224GW+245GY+592HT+509HN+504HK+852HU+36IS+354IN+91ID+62IR+98IQ+964IE+353IL+972IT+39JM+1876JP+81JO+962KZ+7KE+254KI+686KP+850KR+82KW+965KG+996LA+856LV+371LB+961LS+266LR+231LY+218LI+423LT+370LU+352MO+853MK+389MG+261MW+265MY+60MV+960ML+223MT+356MH+692MQ+596MR+222MU+230YT+262MX+52FM+691MD+373MC+377MN+976MS+1664MA+212MZ+258MM+95NA+264NR+674NP+977NL+31AN+599NC+687NZ+64NI+505NE+227NG+234NU+683NF+672MP+1670NO+47OM+968PK+92PW+680PA+507PG+675PY+595PE+51PH+63PN+64PL+48PT+351PR+1787QA+974RE+262RO+40RU+7RW+250KN+1869LC+1758VC+1784WS+685SM+378ST+239SA+966SN+221SC+248SL+232SG+65SK+421SI+386SB+677SO+252ZA+27ES+34LK+94SH+290PM+508SD+249SR+597SJ+47SZ+268SE+46CH+41SY+963TW+886TJ+992TZ+255TH+66TG+228TK+690TO+676TT+1868TN+216TR+90TM+993TC+1649TV+688UG+256UA+380AE+971GB+44US+1UY+598UZ+998VU+678VA+379VE+58VN+84VG+1284VI+1340WF+681EH+213YE+967ZM+260ZW+263JE+381RS+44ME+382IC+3422CD+243GG+44XS+252XY+590MF+590 After some testing I noticed the output tends to switch states when the voltage at the sensor is around the threshold voltage, this can cause some flickering during the last moments of the day, specially if there are clouds around which make the sensor voltage go up and down. Could you please explain the purpose of the transistor? The circuit shown in figure 2 is using a relay at its output and when light falls on the LDR it will activate the relay . Speaking of the light dependent resistor, it will have a high resistance in darkness and low resistance in the presence of light. The hysteresis resistor's function is to raise the reference voltage by a certain amount when the lights turn on, this is made to prevent the variable voltage to oscillate around that reference causing flickering. Very nice explanation; thank you for sharing. If you want to build this sensor you'll need: Operational amplifiers can work as comparators by removing the feedback loop, this makes the gain to be incredibly large, so large that the slightest difference of voltage between the inputs is enough to make the output signal change states. Reply The circuit is quite simple and can be assembled easily, here are the schematics and board files for Eagle: To increase the load handling capability you can use a higher end MOSFET or parallel several MOSFETs with the same characteristics. TIP: If you remove the hysteresis resistor the circuit will return to it's normal operation, working without adding voltage to the reference voltage after it is trespassed. When acting as a comparator, an operational amplifier usually has a reference voltage and a variable voltage, the reference voltage will remain constant, and in this case is fixed thanks to the potentiometer, this voltage can vary from VCC to 0 volts. This light sensor switch circuit allows the automatic connection of a lamp when the light is low (at nightfall) and will maintain the lamp ON for a certain period of time. pages: 1; 2; LED Photo Sensor. Here's a circuit that takes advantage of the photo-voltaic voltage of an ordinary LED. TIP: Don't place the sensor near the lights you're trying to control, when they are turned on the sensor will turn them off because it detects the light they produce, entering in an annoying strobe-like loop. Reply In order for the lights to turn off again, the sensor must now rise a considerable amount of voltage to reach the threshold again, and this gives it a larger margin to cope with interferences caused by the environment. Did you make this project? I hope you like them! LDR is a Light Dependent Resistor which resistance increases as darkness and its resistance is Decreases when Light falling on it.

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