# Questions tagged [ldr]

A light dependent resistor (LDR) is a resistor where the resistance decreases with increasing light intensity.

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### Automatic dark detector: base voltage

Here we have the typical “automatic dark detector” circuit: Let’s assume LDR=5Kohm with light, and LDR=2Mohm in darkness, the battery is 12V instead of 9V, and the transistor has a forward voltage ...
2k views

### How can you turn perceived brightness (log scale) into a linear analog output using an LDR?

This question is not about how to make illuminance (in lux) a linear function of voltage! It's about linearly representing the human perception of brightness, which itself scales logarithmic to the ...
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671 views

### What is the mathematical relationship between the resistance of an LDR and light intensity in lux?

I have been surfing the internet and my physics books for the relationship between the resistance of an LDR and light intensity (a formula), and so far I have found nothing. If any of you have a ...
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### Problem with LDR + PIR

I am using a TEMT6000 LDR and a PIR to turn on outdoor lighting, well that's the plan. The LDR and PIR are in the same housing, and after some searching on forums, I found that I can combine the V-...
• 11
51 views

### LiFi with Arduino

I am trying to learn LiFi by transferring data between two Arduino UNO boards with sample code as in link below. https://create.arduino.cc/projecthub/hamiran1997/li-fi-system-36ff5b?f=1#comments ...
44 views

### Automatic LDR switching circuit

I would like to create an energy efficient LDR evaluation circuit. The circuit should provide the possibility to connect an external LDR (R8) or use an internal, permanently installed LDR (R25). When ...
99 views

### My light-dependent resistor gives a fluctuating serial output

I'm a high school student trying to make a light tracking single axis solar panel. I am using an Arduino Uno rev3 board. When I first finished building it, the system failed to operate. I spent a few ...
69 views

### Need help on solar light auto on off dawn to dusk

I have 36 Ah battery. I will charge it through solar change controller or through inverter. I want to connect this battery to two 9 watt DC LED garden lights which will turn on and off automatically ...
135 views

### ESP32 digital IO output inconsistent voltage

I have a problem which I have been fighting with for several days now. I can't see any possible solution. Maybe someone could give me push in the right direction, that would mean a lot. I ordered 5 ...
1k views

### Night light broke after trying to dim LEDs

I purchased a cheap night light that plugs directly into a 240V wall outlet. It has three color changing LEDs. The problem was, those LEDs were way too bright. I decided to modify that night light a ...
• 905
82 views

### Will this circuit work on a Raspberry Pi?

There a lot of articles on websites regarding the use of LDRs connected to a Raspberry Pi. As an example, using an ADC or using a built in library. I'm interested with my own design below and since I ...
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1 vote
236 views

### How to prevent relay damage due to switching that is not smooth

I am driving a 9V relay from the output of a comparator (LDR sensor) and the relay gets damaged due to rapidly changing voltage from the comparator when light on the LDR is small. The relay starts ...
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### PWM regulated by a LDR , the darker it is outside, the darker are the LEDs

I'm doing a hobby project with an electronic panel. The panel is going to have some white LEDs under switches names. Since im going to use the panel at all times of the day I want the LEDs to be ...
66 views

### What resistor should I put in series with an LDR for minimum current draw when using an Arduino Nano?

Is it possible to use 10k ohm resistors without having any noise issues? I plan on making a solar tracker with 4 LDRs in parallel so a low current draw is imperative - so is a low noise distortion.
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148 views

### Is this LDR and TRIAC circuit advisable for real time application?

Would you suggest below circuit? Will it work for a long time? What are the advantage and disadvantages of this circuit? https://envirementalb.com/automatic-street-light-circuit/
112 views

### How would you connect a light dependent resistor / photoresistor/ CdS cell at a right angle to a surface mount board?

My project uses light dependent resistors (aka photoresistors or CdS cells). All the ones I can find for sale from the usual suppliers are through hole type. ie. they have two wire legs. The PCB I'm ...
166 views

### I'm making a simple dark sensor project with a light dependent resistor (LDR) and I want to replace the LED with a buzzer but it doesn't work

I replaced the resistors with small ones to give the buzzer more current,but itstill doesn't work. I checked my buzzer and it's working fine. The circuit works perfecly with the LED in the breadboard ...
62 views

### My NE555 circuit triggers falsely when connected to the mains using a 5V adapter

I have designed a laser security system using an NE555 in monostable mode with a potentiometer to adjust the pulse length. Another NE555 (U2) ciruit is used for delaying power on the monostable ...
75 views

### Trouble understanding a given circuit for an LDR pulse sensor

I'm a second year physics student, part of a group, and we're trying to build a pulse monitor following this guide. This is the schematic I'm having trouble to understand: I have basic knowledge of ...
138 views

### Is it possible to solve for the values of this grid of photoresistors in software?

In this question a circuit was set up as shown: The idea is to power the rows one at a time, and read off the voltages of each column. But there's a subtle problem. There are alternate paths to ...
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131 views

### How to connect LDR to LED by using battery 5V

I connect LDR to LED by using battery 5V like this circuit. I adjust value of VR and LDR but it's not work. LED still 0.00V. How to fix circuit for make LED to 5V
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62 views

### LDR connect to opamp switch very fast when low battery

I use LDR connect to opamp like this circuit. I use input is 5V from 7805 connect to battery 12V. When relay turn on the light about 2 hour then relay switch on and off continue very fast. How to fix ...
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1 vote
186 views

### Where to put a buzzer so that it goes off when there is light (and should stop when there is dark)

I've successfully created (and breadboarded) this circuit: simulate this circuit – Schematic created using CircuitLab I cannot figure out where to put a buzzer so that it goes off when the LED ...
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1 vote
120 views

### What's wrong with my basic light/dark detection circuit

I've just started playing with electronics, and wanted to make a light/dark detection circuit without using a transistor (they are too advanced for me at this moment.) I decided to use these ...
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2k views

### How fast is a photoresistor?

I am trying to build a skipping rope jumps counter. My preliminary design consists of an LDR, a laser diode, and sn Arduino. Basically, the LDR and the laser diode are placed exactly opposite to each ...
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### How to implement an equation in assembly language using PIC18F and display its result on LCD?

I had a project that requires to measure illuminance(lux) using LDR and display the result on LCD. Thanks to some references from Google, I had managed to build a equation that shows relation between ...
62 views

### Solar tracking using an Arduino Uno

I'm trying to design a dual axis solar tracker using an Arduino Uno-R3. Basically it just takes the input from the LDR and outputs the PWM signal to the two 9g servo motors for each axis. The ...
65 views

### How to select resistor value for LDR

I want to try making an 230 VAC bulb that automatically turns on/off using a relay a transistor an LDR I have collected the following components: a 9 V battery a 9 VDC relay an LDR a BC457 ...
1 vote
219 views

### NE555 in a light detecting circuit

I'm completely new to electronics but my degree gives me a basic course with a project at the end. I built this small circuit to detect when a light is shined on the LDR to turn on an LED so ...
1 vote
609 views

### Is there an equation for the relationship between illuminance and the resistance of a light dependent resistor?

All I've seen on this is: R = A.Ea. where E – illumination (lux), R – resistance (ohms) and A, a – constants. The value of ‘a’ depends on the CdS used and on the manufacturing process. Values usually ...
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6k views

### How do I calculate resistance when I have the voltage drop?

This is my circuit: 3 volts in with a 1k ohm resistor in series with the LDR. I have the voltage drop across the LDR but I need to find the resistance.
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### Night light circuit wih switching bulbs

How can I connect a night light circuit such that one bulb is lit up on a sunny day and one is only lit up at night so that the two lights don't light up simultaneously? Also, can I use a SPDT switch ...
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221 views

### How to adjust duty cycle of an existing square-wave, based on light level

I am making a wall-powered, battery-backed, BCD alarm clock with discrete logic. I'd like to adjust the brightness of the LEDs based on light level, as this clock will be used on a nightstand. So ...
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116 views

### MOSFET Fails After Few Uses

I am attempting to use a N-Channel Logic Level MOSFET as a switch for a phone charger that runs on a 42V battery. I have a resistor circuit with an LDR that currently outputs 3.3v when LIT with a ...
107 views

### Best circuit to turn on a (5v heating pad) switch during the day?

Most of the circuit examples I'm finding online for LDR or other light-detecting circuits appear to be for turning things on at night. I'm trying to rig up a small heating pad under a birdbath using a ...
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475 views

### How to build fast visible light detector

I need a circuit which can detect flickering of light too fast. I have Digital LDR Module which is too slow can I replace LDR with L14G2. Digital LDR Module - Digital LDR Circuit - Can we ...
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### Dark circuit using LDR

Could anyone please help me to draw the wiring diagram for this connections? I have made this circuit but the problem is that I must attach the diagram of how all of these are connecting with each ...
1 vote
146 views

### Need help in designing of circuitry. (Power Electronics)

The circuit is supposed to detect ambient light and react accordingly. When there is high illuminance the LED should be dim and when there is low illuminance the LED should be bright. The transistor ...
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233 views

### How to add a LED indicator to report LDR sensor error using PIC?

I have this simple light sensor project using LDR. The PIC reads an analog signal 0-5V from LDR and will turn on the relay ON when it's bright on and off when it's dark. I want to add a simple LED ...
119 views

### Can someone explain this project to me? Can you explain the schematic so I understand how it works? [closed]

https://electronicsprojectshub.com/how-to-make-an-automatic-night-light-using-ldr/ Can someone explain this project to me? Can you explain the schematic so I understand how it works? A very very ...
1 vote
314 views

### What resistors do I need for a simple LDR triggered h-bridge?

I am attempting to build this circuit: https://www.instructables.com/id/H-Bridge-on-a-Breadboard/ But instead of switches, I want ldr s like this circuit: https://www.instructables.com/id/Simple-...
89 views

### Light Sensitivity Indicator (using transistor, LEDs, LDR)

I have; 1) 9 V dc source 2) two LEDs (red and green) 3) LDR 4) few resistors (kilo ohm) 5) npn transistor I need to build a circuit such that the red LED lights up only at night (0 light ...
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188 views

### NE555 LDR threshold voltage

The problem is that when I set the LDR on my car and stop for a short time near street lighting my headlights from the car are switched off. I made a circuit simulation, when I click 4 times for the ...
1k views

### 555 timer delay circuit + light sensor?

I am quite new to electronics and I would like to combine these 2 circuits together so that during complete darkness on the LDR, the LED would turn on instantly and when light falls on the LDR there ...
137 views

### LPC1768 - Green LED when LDR sees light, Red LED when LDR is covered

I have been trying to achieve a task I am working on and I believe I am almost there. It successfully changes colors whenever I cover it but when it does, the red LED keeps blinking instead of it ...
1 vote
93 views

### LDR breaks over time what to do?

http://cactus.io/hookups/sensors/light/ldr/hookup-arduino-to-ldr-sensor I have the following circuit which was running for a long time but at one point something broke and it started producing high ...
1 vote
975 views

### NE555 and LDR circuit diagram

I have modified a schematic for my project with the following image: Instead of a 20K potentiometer, I use 100K for more precise adjustment. Do I need to add a disk capacitor of 10nf or 100nf to Pin ...
90 views

### How to find the best way to fade in/out?

I have a bunch of these PAR lights below. They work with DMX and have per LED PAR 3 red, 3 green, 3 blue and 3 white LEDs. I can set the value for the red, green, blue and white lights independently (...
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