Questions tagged [photoresistor]

A photoresistor or light-dependent resistor (LDR) or photocell is a light-controlled variable resistor.

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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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More current in non-inverter comparator hysteresis using a photoresistor

I'm doing a small circuit where I need automatic LED's to turn ON in a low light environment. So I decided to use a photoresistor (more light less resistance) connected to a non-inverter hysteresis ...
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Two different LDR circuits: what's the fundamental difference?

Here’s what’s going on. I’m working on a programmable light timer (of course I could use something like Alexa, but I’d rather go for the challenge and build something to my own design), where the LDR ...
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2 answers
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How to calculate value of voltage by light intensity?

I want to write the code to turn the LED on when the light intensity that falls on the photoresistor decreases. So in daylight LED is off, and when it's getting dark LED goes on. I know that ...
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1 answer
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Determine the output voltage of a signal conditioning module

Already, apparently from the feedback I got from this: How to model the output signal of this circuit? It is better to just explain the whole thing. I am doing a project involving a LDR sensor that is ...
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2 answers
86 views

How to model the output signal of this circuit?

Following up this question: Thévenin equivalent: is this resistor useless? I've now changed the voltage source to a resistor since this is a photoresistor. However I have no idea now how to ...
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3 answers
112 views

Dark sensor with transistor

Why do most of dark sensor circuits in the Internet look like this? It seems to me that in such circuit, photoresistor doesn't limit base current and it doesn't work. I think that photoresistor ...
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5 answers
115 views

How to estimate the recommended current in an optocoupler?

I intend to use an optocoupler to simulate a push button on a control card (I could measure 5V between pins but I don't know for sure if there is a pullup resistor in the card). Also the other way ...
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1 answer
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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 ...
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1 answer
38 views

Circut to turn on a battery powered electric fence

I want to be able to have a battery powered electric fence automatically turn on in the morning when it's day light, and power off when it gets dark. I don't seem to be able to find a product that ...
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2 answers
113 views

Photosensitive Diode or photo resistor?

As I understand it, a photosensitive diode generates a small current with light. I ordered these off Amazon: https://www.amazon.com/gp/product/B01F3TU2XC/ref=ask_ql_qh_dp_hza These change resistance ...
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Photoresistor audio switch on battery power

I'm trying to build a light-driven chime silencer for a wall clock. The schematic from https://electronics.stackexchange.com/a/177401/18259 seem like a very good starting design for this: It, however,...
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1 answer
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Confused about the functioning of a QRE1113 reflectance sensor

First year IT student here. I've been stuck on a problem involving a QRE1113 sensor, in which we were given the schematics below: From my understanding so far, the reflectance sensor is divided into ...
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2 votes
1 answer
468 views

Accuracy of manufactured photocells (LDR) with respect to light intensity

I was looking through photocell (photoresistors) datasheets, like for instance the NORPS-12, especially the graphic on resistance value versus light intensity. In no datasheet could I find information ...
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4 answers
131 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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1 vote
1 answer
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How do I make a high signal last longer so my nodeMCU/Tasmota sees it?

Problem I have a data input signal to a nodeMCU running Tasmota. It only works intermittently because the signal often isn't high long enough for Tasmota to sense it. So I need to find a way to make ...
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3 votes
3 answers
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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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1 vote
2 answers
61 views

Design review for photoresistor-controlled linear regulator

I would appreciate some comments/insights/criticism on my design: I want to turn on/off a linear regulator (MIC5504) based on the light. I have tried just using a resistor and photoresistor voltage ...
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2 votes
1 answer
187 views

Is there constant current flow in this circuit?

I am studying basic circuits, and have a very elementary question. When the photoresistor is exposed to light in the following circuit, is there a constant drain on the power supply? If this were used ...
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Photo-resistor and leds

I'm trying to build some system that would detect light and turn a 12v led strip ON. The only power that I have available is a 9v battery. I found some Arduino compatible boards but it seems overkill ...
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0 answers
77 views

Light sensor connected to GPIO input of raspberry pi

I have created simple light dector. Schemea is below: Real circuit on breadboard: I have written code in python using GPIO library: ...
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1 vote
2 answers
181 views

Light detection by GPIO raspberry pi

I have a cirtuit which consists of Resistor, Photoresistor, PNP Transistor, Voltage supply from raspberry pi like on the schema below: Purpose of this circut is to detect light as a dawn detection ...
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3 votes
1 answer
87 views

Radioactivity counter

I am designing a Geiger counter which measures radioactivity. I am planning to this using the photoelectric effect. The band gap of insulators is pretty big and only gamma particles are energetic ...
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2 answers
523 views

What options exist for a for low-latency (<1ms) photosensor?

I'm wanting to build a computer keyboard-to-display lag measuring tool using an Ardunio: User places the photosensor right-up to their computer monitor. User presses a button on the Ardunio. The ...
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1 answer
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Reading full photocell range with ADC

I am trying to use PDV-P8103 photocell as a sensor for LCD dimming circuit. The application requirements are to have comfortable brightness level from almost total darkness up to direct sunlight. The ...
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149 views

Proper phototransistor for detection of small object

I am attempting to detect a falling objects 6mm in diameter, falling every 160ms. The object to be detected will be confinined to a black tube, void of light, 18mm wide x 35mm long, my plan is to ...
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1 answer
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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1 vote
1 answer
499 views

Convert a Dusk-to-dawn outlet device to Dawn-To-Dusk? [closed]

I recently purchased a Dusk-to-dawn outlet sensor (https://www.amazon.com/dp/B00002NB2X?ref_=pe_2640190_261118450_302_E_DDE_dt_1), but I'm wanting to convert this thing into a Dawn-to-Dusk device ...
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4 votes
1 answer
1k views

Using op-amps to read real-time resistance values over a wide range

Background I have been using a simple inverting op-amp circuit and Arduino to measure the resistance of a photoresistor (light 5k, dark 200M), like in the schematic below. This provides linear data ...
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5 votes
4 answers
1k views

Why do LDR photocells use CdS and CdSe?

Basically what the title says. Cadmium is a toxic, environmentally harmful heavy metal that's banned under the RoHS directive, and even before RoHS its toxicity was well known. What makes cadmium ...
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7 votes
3 answers
3k views

Understanding basic photoresistor circuit

I'm new to electronics, so I just can't wrap my head around how this photoresistor circuit works. I understand the following: the photodiode can be understood as a variable resistor (i.e. works in ...
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0 votes
1 answer
272 views

MSP-EXP432 "Analog In" pin taking voltage from circuit [duplicate]

I am building a circuit consisting of a voltage divider (with a fixed resistor and a LDR or photoresistor) outputting voltage to an ADC. I want to measure the voltage going to the ADC using an MSP-...
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2 votes
0 answers
845 views

PV cells (photovoltaic) I-V curve plot simulation

I am trying to plot the I-V curve using python because that helps me in understanding PV cells / solar panels (and diodes as a general thing). I know the formulas ...
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1 vote
0 answers
125 views

phoresistor vactrol tremolo noise

I made an optocoupler by shrink tubing a generic photo resistor and a cold white led. Then used it in the following setup to be able to control audio level to achieve tremolo effect: simulate this ...
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1 answer
484 views

how to wire together multiple photoresistors to make one big sensor?

I'm using an esp32 dev board, and a bunch of 5v laser diode emitters pointed an equal number of photocell resistors across a plane. The goal is only to detect when any two or more beams break at the ...
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1 vote
0 answers
399 views

How to identify different LDR photoresistors that have been mixed together?

I purchased a variety pack of LDR photoresistors from eBay which includes GL5506, GL5516, GL5528, GL5537, GL5539. The problem is that they all came in the same little bag and are visually identical. ...
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1 answer
107 views

Reduce active region of NPN transistor

I've got a small LED garden lamp, battery operated, that turns on with a switch. I am currently trying to use a photoresistor that I have to make it turn on when it gets dark (so I don't have to ...
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0 votes
2 answers
1k views

Solar powered LED via capacitor?

I am building a large garden peice in wood, which I hope to illumine from within, powered by a small, (perhaps 90x65, 6v, 0.6w 100mA as space is limited) solar panel. After testing, I noticed that ...
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5 votes
1 answer
1k views

Is my IC broken?

I'm making my first circuit for a line following robot. I already made the prototype, soldered it together, and now I'm at the assembly stage. Here is the circuit diagram I'm using: What should ...
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0 votes
5 answers
435 views

Photoresistor power switch for arduino, does this look correct

edit: uploaded schematic: I am a novice, this diagram may not be correct but should convey the attempt. I want to turn-on power to an arduino microcontroller when it is dark. I white-boarded an ...
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0 votes
1 answer
122 views

PCF 8591 switch using transistor

I'm using a PCF 8591 ADC for the sake of the photo resistor on it - here. The project doesn't seem too complicated for a software engineer like myself but I seem to need some help. I'm using an ...
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1 vote
1 answer
1k views

Photo resistor night light not working

I am completely new to this stack exchange and to electronics and general so please keep that in mind if my question is not up to par for this site. I've attempted to make a night light using a ...
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0 votes
1 answer
70 views

Night Activated Switch

I draw a schematic which uses LM741 and IRF830. The main function of the schematic is to light up a few leds (which consumes about 100mA in total) when the night comes. Please have a look at the ...
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1 vote
4 answers
278 views

Arduino sensor data erratic

I'm a noob just getting my feet wet in EE, so go easy on me, please. I bought an Arduino Uno and have been learning tons in the last couple weeks. I took an LM35 sensor, a generic thermistor (using ...
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0 votes
2 answers
1k views

Photo resistor is giving off an unsteady output, how can I fix that?

I just started out with Arduino, and for my first project, I need to use a photo resistor to get an accurate reading of ambient light in my room. Problem is, the photo resistor is not giving off a ...
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3 answers
118 views

Toggle "on/off" with small resistance change

I'm trying to make a small model car stop when it crosses a black line on the ground. My idea is to use a photresistor + some magic to do the trick. I'm here for the magic part... The resistor I have ...
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1 vote
1 answer
6k views

How to increase sensitivity of Light Dependent Resistor (LDR) [closed]

I am using LDR sensor in my project. The source of light comes from the different colour of images. As we know, the spectrum of each colour is different and it will produce a different intensity of ...
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0 votes
5 answers
710 views

Transistor Collector Heats Up

I used power transistor to drive high power LED (used in streetlights) I added resistor between the Transistor Collector and the LED to verify which part of the transistor causing too much heat, and ...
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3 answers
275 views

Clean water turbidity sensor

I'm working on a project to determine the water clarity, using a MCU with a turbidity sensor. I have tested sensors such as: Cheap Dishwasher sensor, and while it works for changes in turbidity in ...
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1 vote
1 answer
580 views

Photoresistor Transistor Circuit

I am teaching myself electronics. I designed this circuit to use a photoresistor to trigger a transistor when I hit the photoresistor with a laser pointer. On the Arduino side, I want it to look like ...
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