how to make ldr do high power work(12v motor) without becoming hot?

My ldr works fine in controlling 1.5 & 5v motor but connecting in series but when i switch to 9v and 12v motor it becomes hot  maybe i can decrease its heat by adding resistor parallel to ldr so motor will get required current and ldr wont have to suffer all current or maybe i have also changed power source in second case to a 12v and 3amp  i thought i am not ta\ing 3 amp current according to I=V/R but P=VI so if current decrese my power source's voltage .

Asked by Atul009 4 years ago

Hi, I need some help to understand how is this working. Answered

This is the source of my question. My question is : why is the LED lighting up as it gets dark ? I taught that a LDR (light dependent resistor) is supposed to let current pass only when light is shining on it (source), so why here is it letting current pass only when it's dark. And what is the role of the transistor in this circuit ? Any clarification is much appreciated, Thank you.

Asked by Eunix 4 years ago

Suitable transistor or IC to run 1 Watt LED in low voltage? Answered

I want to run 4 x 1Watt LEDs from a 3.7V source (10000mAh). LED DC Forward Current: 350mA The purpose is to sue it with a motion sensor. Please suggest a transistor or IC with maximum efficiency. Update: I found that the "IRF 540" Mosfet is a good solution.

Asked by shijilt 1 year ago

How do you inverse the function of a LDR (Light Dependent Resistor) ....? Answered

I know the schematic diagram ... But I don't know how it works ... please can someone explain me the inverse function of a LDR I've posted the schematic diagram also! Thanks

Asked by harshesh 7 years ago

How to use LDR to be run with 12v DC motor?

I want make a project that will run in light but as light turns off, circuit should be break   Im using : 1. 12V / 2Amp motor 2. LDR 3. 12 v supply 4. Laser light Whenever light appends on LDR circuit should pass 12v for the motor and whenever light is brocken circuit should have total resistance so what Kind of components should i use or suggest me LDR based for above circuit

Asked by Drg3 1 year ago

LDR Grid + Smartphone = ?

Hi, I've got an idea but I don't know what it can be used for, yet. Maybe you'll have some ideas for useful applications based on this concept. The idea is to make a grid of LDRs which fits the size of a smartphone/tablet screen, write some code which draws a similar grid on the screen (or just switch images of that grid) so that each LDR will be affected by the light (and color) provided by each cell from the screen.

Posted by nivini 2 years ago

What is this black thing next to the capacitor??? is it an LDR?

Http:// ha the shape of half a cilider, and two terminals comming out of it... what is it?it was in an IR controlled mini car...

Asked by amando96 9 years ago

LDR or optical reflective sensor?

I am planing to make a line following robot without micro controllers. So I am using a light sensor connected to an AND GATE (the other input being the current to the motor). So since I am using" an and "gate I want the input current to be an absolute zero or some value ,ie the current should not be varrying with the light intensity. Besides I think I might drop the "and gate" thing and use an OPAMP instead as it would give me a varrying output current which is all I need

Asked by chrissunny94 4 years ago

how to construct a simple circuit using LDR and transistor? Answered

Materials: LED, LDR, BC337 transistor, 10k trimmer, 500ohms resistor.. 

Asked by animeguild53 7 years ago

how to make Automatic light dimmer using LDR?

I tried to make this light dimmer circuit but it's not worked because of my  LDR exploded  why is that..  any similar circuit diagram ? thanks.... This is the circuit i used..

Asked by ishan udyoga 4 years ago

how to use LDR as a relay for RC car to increase voltage to motor

Hi there,  I would like to know more about how LDR's work, its quite difficult to source 3 volt relays in South Africa, so I had an Epiphany, why not use 2x  LDR 1x for Forward and 1x for Reverse on an RC car, I don't know much about how responsive the solution is, how many seconds or milliseconds delay  there is? Does it work like a switch?  would it be a viable option on an RC car? I'm sure this could apply to little 3 volt RC cars upwards, I know brushless is the way to go, however this would indeed be a great learning experience.  kindest Regards, Lee Reddy. 

Posted by Leereddy1818 1 year ago

Multiple Photocell Problem (Arduino)?

Hello, I have a problem with using more than 1 photocell. I am using the AnalogReadSerial example to test each one and they are giving me junk. I have tried just one wired to the board and it works fine, but when i wire 4 into a breadboard it gets messy.                                                                                                                                                                                  Here are some pictures                                                                                                                    

Asked by D5quar3 4 years ago

arduino and 4051 IC?

I have followed your instructions in and I successfully. I now make the same project but with 11 light sensors use arduino uno rev 3 and 4051 IC. Please help me to modify the original code to work with arduino uno rev 3 and 4051 ICs. Thank you very much link about arduino and 4051 1. 2. 3.

Asked by ylinggarjati 4 years ago

LDR Calibration ?

I am planning to build a lumenmeter but I am not getting how to calibirate the LDR and do not have any lumen meter so if could tell the estimate lumens out of a 5w CFL or any other device might help

Asked by Bot1398 5 years ago

How to convert LDR reading to lux readings?

I want to make a digital lux meter using a arduino but I am quiet confused on how do I convert LDR reading into lux reading.Please help me for the conversions. 

Asked by Bot1398 5 years ago

Arduino LDR tachometer (RPM counter)- not sensitive enough ?!?

Ladies & Gentlemans  ... I would like to ask you, what I'm doing wrong, in this RPM counter ??? As mentioned in my previous questions, I 've got an ARDUINO and I started with my first part - of my project. To count RPM / or speed. I'm using a LDR (light dependant resistor) and green laser as light source. The scheme is like this: + 5V ------- LDR -------------Analog pin 1                                     \                                       \--------resistor (220kOhm) --------- GND The code for this project looks like this : int LDR=1; // LDR is on analog port 1 int val=0; // this is the value, I get from the LRD void sextup(){  Serial.begin(9600); } void loop() {  val = analogRead(LDR); // read the value getting from LDR Serial.println(val); if (val } To explain the value 1018 in the IF condition ... when pointed the laser on the LDR,I get value from 1019-1020. So my idea was, when the value decrease just by one or more ... let me know, that the laser beam has been interrupt. But I realised, that I can cross the laser beam very quickly, and the LDR/Arduino will not notice it. I really don't know, where I'm going wrong. My few suggestions are : 1. wrong method - to use LDR ... should I use something else ??? 2. wrong RESISTOR value ??? ... should I change to different value to make it more sensitive ??? (I tried 2 different values = 220kOhm, 46kOhm ... that's what my voltmeter said :) ... but with both of them I have the same result ) 3. should I use different code ??? Any ideas ??? Thank you in advance for your answers. Zholy

Asked by zholy 8 years ago

Transistor help.... very basic, LDR/LED

I'm trying to make a very simple circuit to light an LED based on light from an LDR. I have all the components, it's a white LED, I'm using two AA batteries, and the LED glows brightly when I attach it to the batteries, but when I attach it to the LDR, it is either dim or dimmer due to the resistance... I'm sure I need to use a resistor for this... I have some assorted PNPs and NPN2222As... I've looked at a couple tutorials, but none of them seem to work... does anyone know how to do this without any (or as few as possible) other components? Thanks

Posted by perkinsb1024 10 years ago

Laser trip switch? Answered

Hi I want to use a laser and a ldr to switch on a relay using arduino once the laser is tripped the relay turns on and once it trips again its off  could some one help me with the code and schematics i want to use pin 9 as in1 on the relay  thanks a ton in advance

Asked by TheGreatResistor 2 years ago

Run a few 1 watt LEDs using transistor from 3.7v ?

Hi , I want to control 5 X 1W leds using a LDR. It will be running on a 3.7v 4500mAh battery . I have the LDR circuit. The problem I face is , normal transistor are not capable of running 5W leds (1W X 5) , it just heats up. i tried some high power transistors , they seem to provide less voltage to the leds. I need a transistor , which can be used as a switch , it should work well in 3 v , should be able to handle max 5W. Any one have any idea ?

Asked by shijilt 3 years ago

Does anyone do Automated Car Wash System by using Arduino with LDR?

I wish to know how am i able to write a program which i could control the water spraying, brushing and drying by using arduino.  My project is to use a laser pointer which will send the signal to the LDR and it will trigger the water to spray, brush and dry the toy car on the conveyor belt. Can anyone help me?? I'm a diploma student, and my supervisor is a mad man which who asked me to do such project which he doesn't know either.  The first image is how i think my circuit looks like The second image shows what i had done

Posted by ahchuan.ycc 3 years ago

Fitlight trainer using arduino

I want to make a fitlight trainer with arduino. I want to make it with leds and LDR ligtht sensors. A random light pops up and when you hover over the sensor it sets it to LOW and then another random light pops up and over and over. Can anyone help me with this idea? I have the code for one light: int LDR = 0;     //analog pin to which LDR is connected, here we set it to 0 so it means A0 int LDRValue = 0;      //that’s a variable to store LDR values int light_sensitivity = 20;    //This is the approx value of light surrounding your LDR void setup()   {     Serial.begin(9600);              pinMode(13, OUTPUT);      } void loop()   {     LDRValue = analogRead(LDR);      //reads the ldr’s value through LDR     Serial.println(LDRValue);       //prints the LDR values to serial monitor     delay(50);        //This is the speed by which LDR sends value to arduino     if (LDRValue > light_sensitivity)       {         digitalWrite(13, HIGH);       }     else       {         digitalWrite(13, LOW);       }   }

Posted by JordyK4 2 years ago

What to do with old robot? / Cybot

I found an old robot that was part of one of those 'build it yourself' magazine series. I was gonna eBay it but found there was actually quite alot of cool stuff in there so I've compiled a list and I'm gonna make an instructable using some of the parts, But I need ideas / help.Here are (the best) parts.2x sets of ultrasonic emitters / receivers2x LDRs large2x smaller photoresistors (used for line following)2x set of inrfa red emitter& reciever leds2x bright white leds + various others2x 9v motors & gear housingsLCD display 5cm squreeepromspeed controllers selector switches etcand a load of pre programmed processors that can't be reused.some more technical details here

Posted by madmanmoe64 9 years ago

LDR and/or PWM for energy efficient 'smart' dimmer?

Is there any way to combine a Light Dependent Resistor or other light sensor with a Pulse width modulator to (energy efficiently) dim indoor lighting in the presence of sufficient natural light?  Thanks!

Asked by bbawco2 8 years ago

How to get the right voltages to make a circuit with laser pointer, LDR and motor?

In short, it is for a uni project, and what I would like to do is shine a light (laser or white light) onto a prism that would have a LDR to detect the light and trigger a motor - the motor is attached to the prism to make it spin and refract the light to the next prism for a chain reaction mechanism to happen (I'd have 3 of them operating in a circle, maybe..) What I really need to know is what types of components to buy as there seems to be different kinds of every one, different voltages. (for example, how strong a laser do I need to be detected by the LDR, etc etc...) Don't want to fry anything! Thank you very much for you help! :)

Asked by matisha23 6 years ago

How to increase the light sensitivity of a DARK SENSOR CIRCUIT?

I recently managed to replicate a dark sensor circuit using a LDR, a 220K & 330 ohms resistor, a BC547 transistor and a LED. But the problem is that it is very little sensitive to light. During daytime there is no problem but at night, under the CFL light it doesn't sense the light and turns on. To turn off the light, I have to illuminate the LDR with a external light source and that too very close. What I want is that the LED should light up only when there is complete darkness. How should I modify the circuit to increase the sensitivity?  The circuit diagram is as given below.

Asked by Arijit Chatterjee 4 years ago

Arduino DFPlayer MP3 player with Light sensor (LDR Module) as trigger

Hi everyone :) Yet another question... So I got my self a DFPlayer mini (mp3 player module) for Arduino, and a nice tutorial on how make it work, but I want to use s Light sensor (LDR Module) instead of a button (I just need play and pause or stop for my gift box) So at the moment if I connect the LDR instead of the button and give it some light, it turns the music on and off constantly/repeatedly because the LDR is constantly sending a HIGH signal, not just once like the button. Here is the question part: How to modify the code, so it only turns on the music when it gets HIGH signal and off if it gets LOW ??? Here is the modified code (I took out the auto play and the next and previous commands: ///              MP3 PLAYER PROJECT /// #include "SoftwareSerial.h" SoftwareSerial mySerial(10, 11); # define Start_Byte 0x7E # define Version_Byte 0xFF # define Command_Length 0x06 # define End_Byte 0xEF # define Acknowledge 0x00 //Returns info with command 0x41 [0x01: info, 0x00: no info] # define ACTIVATED LOW int buttonPlay = 3; boolean isPlaying = false; void setup () {   pinMode(buttonPlay, INPUT);   digitalWrite(buttonPlay, HIGH);   mySerial.begin (9600);   delay(1000);   playFirst();   isPlaying = true; } void loop () {   if (digitalRead(buttonPlay) == ACTIVATED)   {     if (isPlaying)     {       pause();       isPlaying = false;     } else     {       isPlaying = true;       play();     }   } } void playFirst() {   setVolume(20); } void pause() {   execute_CMD(0x0E, 0, 0);   delay(500); } void play() {   execute_CMD(0x0D, 0, 1);   delay(500); } void setVolume(int volume) {   execute_CMD(0x06, 0, volume); // Set the volume (0x00~0x30)   delay(2000); } void execute_CMD(byte CMD, byte Par1, byte Par2) // Excecute the command and parameters {   // Calculate the checksum (2 bytes)   word checksum = -(Version_Byte + Command_Length + CMD + Acknowledge + Par1 + Par2);   // Build the command line   byte Command_line[10] = { Start_Byte, Version_Byte, Command_Length, CMD, Acknowledge,                             Par1, Par2, highByte(checksum), lowByte(checksum), End_Byte                           };   //Send the command line to the module   for (byte k = 0; k   {     mySerial.write( Command_line[k]);   } } Thank you ever so much!!!

Asked by GellertK 1 year ago


Hey!!i started working on a project based on ldr and i realised dc motor and ldrs don't work together so before i buy ac motors i wanted to ask that will it work??thanks in advance.

Posted by robo10302 4 years ago

Changing the sensor

Hello guys, I want to make this circuit I just don't want any light to be visible. So, I was wondering if I could just change this LDR sensor to a IR sensor and still get the desired results.  Thanks,

Posted by HavocRC 5 years ago

Can an LDR be used to activate a circuit after everything has been built?

I working on the gender announcement for our next baby and having some slight issues with the activation action.  I have built a circuit based on an ATtiny85 that causes two separate LEDs blink back and forth at a quickening pace underneath a Batman logo or Wonder Woman logo until the LED stays light under the Superhero representing the sex of the's a BOY!   I have had some custom cardboard boxes made and created form inserts and completed the circuits but I am at a dead stop with the activation.  I have thought about contacts around the side of the inside of the box with a non conductive material that would come down from the lid to prevent activation.  My issue would be the reset and 100% success rate.   My guiness thought would be to make the circuit Light reactive but I have NO experience with this and since the circuits are done minus power and/or switch can I still add in a Light Reactive switch using an LDR?   Any help would be greatly appreciated, my wife is driving me crazy about getting these done since i"ve been procrastinating

Asked by njeast13 3 years ago

Can any one help me with a LDR linked on off light project?

I need a simple circuit please help me. Moreover I am totally ignorant about Electronics but can try to make if guided with correct description. Am a layman in Electronics. 

Asked by bannutechniclor 3 years ago

Help with simple transistor circuit.? Answered

I want the LED to turn on when it's dark. But  it remains on and taking out the LDR doesn't affect it. I couldn't post a picture but i made a replica in Fritzing EDIT: The transistor is 3904 NPN.

Asked by Hafiz Mohammad Shayan Tariq 5 years ago

How to build Auotmatic Street Lights Control Using LDR and Arduino for 3 LEDs using 3 LDRs

so , what should I do ? What will be circuit diagram ? What changes should be done in Program ? Thank You ! Please Specify Circuit and Programming . Can I use 3 different Arduino or Use Single Arduino .

Asked by npawar 4 months ago

LDRS (Large Dangerous Rocket Ships) Rocket Competition hosted by Kari Byron

I just finished watching Kari Bryon hosting a Rocket competition on the Science Channel in Lucerne Valley California I Missed the initial showing on July 5th.   But they seem to be replaying it now and then (I saw it on July 10th, at 10 PM EST

Posted by Goodhart 7 years ago


HI GUYS. I HAVE A LDR light sensor I would like to use to turn on a light bulb through a attin85. when I upload the sketch to the Arduino it works fine. but when I upload to the attiny, I can't get it to work. am I'm wiring it wrong? when I put my signal from my ldr sensor to AO and 2 to the led it works on Arduino, but when I do that with the Attiny85 it doesn't do anything. The sketch did upload correctly though so it has to be me wiring it wrong or I need to change the code maybe to cater to the attiny85?my sketch is int LDR = 0; int LDRValue = 0; void setup() { pinMode(2, OUTPUT); void loop() { LDRValue = analogRead(LDR); delay(50); if (LDRValue { digitalWrite(2, HIGH); } else { digitalWrite(2, LOW); } }

Asked by jman2018 7 weeks ago

Plz suggest a place in india to buy all the parts like audrino, LDR etc

Hello i live in kolkata, west bengal, india..and cannot find many a things to successfully make a project. Can u suggest me a place to buy the required parts in kolkata? i cannot buy from ebay as i dont have credit/debit card.. which type of shop do i generally get all the parts..? AUDRINO IS A TOP PRIORITY,,other things are...LDR, TRANSISTORS, variable and fixed resistors, breadboards, capacitors , batteries, RGB LEDs and LASER Modules...

Asked by hbiswas 5 years ago

Attiny 85 not working

HI GUYS. I HAVE A LDR light sensor I would like to use to turn on a light bulb through a attin85. when I upload the sketch to the Arduino it works fine. but when I upload to the attiny, I can't get it to work. am I'm wiring it wrong? when I put my signal from my ldr sensor to AO and 2 to the led it works on Arduino, but when I do that with the Attiny85 it doesn't do anything. The sketch did upload correctly though so it has to be me wiring it wrong or I need to change the code maybe to cater to the attiny85?my sketch is int LDR = 0; int LDRValue = 0; void setup() {pinMode(2, OUTPUT); void loop() { LDRValue = analogRead(LDR); delay(50); if (LDRValue { digitalWrite(2, HIGH); } else { digitalWrite(2, LOW); } }

Asked by jman2018 7 weeks ago

automatic switching of street lights by using ldr and relay

 hey me and my friends were ton a project of automatic switching of a street light depending on the brightness in the surroundings. so we decided to use an ldr(light dependent resistor). here in this circuit ldr has low resistance in brightness(only few ohms) and very high resistance in complete  darkness(nearly 1M ohm).so the transistor Q1 becomes on in day times and Q2 becomes off and hence the relay remains in NC(normally closed) state and the lamp will not glow. at night the transistor Q1 becomes OFF and Q2 becomes ON and hence the relay goes to NO(normally open) state and the lamp glows.and the sensitivity of the device can be varied by adjusting the potentiometer  now i just want to know are there any defects in this circuit so can u please help me in knowing the drawbacks and correcting them and i want to know whether i can connect a relay in place of a fuse as shown at bottom

Asked by spartans 8 years ago

Would this require Programming?

Hi! I'm building a laptop bag alarm for a project I'm working on, and I'm pretty new to electronics. Would anyone know how I could make a system where a switch would be flipped to turn 'the alarm' on or off, and when that switch is flipped, the system would do nothing when the security system is triggered. The security system being 3-8 LDR sensors inside the bag, that will trigger some sort of logical part, that would be able to make the decision whether or not to sound the alarm, based on the status of the switch (flipped or normal)  I'm a programmer, so the system looks like this to me:  IF ALARM_SWITCH_ON && LDR_TRIGGERED { TRIGGER LIGHT && SOUND }  IF ALARM_SWITCH_OFF && LDR_TRIGGERED { DO NOTHING }  ELSE { DO NOTHING } Anyone know how this could be made with circuitry? or whether it would require programming? If it required all circuitry, is there anywhere I could get help with drawing up a circuit diagram?  Cheers & Thanks!  Karan

Posted by KodeKaran 6 years ago