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

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Best way to amplify the photoresistor signal

I have the following schematic. simulate this circuit – Schematic created using CircuitLab And it graphs to an almost stratight line. It is supposed to be a heartbeat sensor. From what I ...
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3answers
98 views

How to use photoresistor for counting passing objects

Can photoresistor be used for counting passing objects?## Heading ## Hello i'm new to the electrical things I wanted to ask if i can use the photoresistor sensor for counting passing objects if ...
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96 views

Choosing resistance in series with a photoresistor for best light-measurement resolution

simulate this circuit – Schematic created using CircuitLab I have a photoresistor, R1, and as a voltage divider a fixed resistance, R2. There is a voltage of 5V over these two, and the voltage ...
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0answers
71 views

How to make a sound-controlled variable resistance?

So I have those old analog video equipements (Panasonic WJ-AVE5, Videonics Video Equalizer) and I'd like to have some of the parameters (video crossfade, superimpose function, brightness level, etc.) ...
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175 views

High voltage voltage controlled linear variable resistor

I have some high voltage (300v+) analog circuits that I want to control digitally which requires the use of a voltage controlled linear resistor that can withstand the high voltages. I don't expect ...
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4answers
1k views

Why do I have to use an additional resistor with a photoresistor?

I'm totally new to electronics and I wonder why we need to put a resistor in series with a photoresistor to measure the variation of light? I mean, photoresistor is already a resistor, why do we have ...
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57 views

Is there a certain type of LDR that will be most effective in a circuit that senses the heartbeat at a fingertip?

I haven't had much experience with LDRs, and was not sure of the different types that will work best in a circuit like that.
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1answer
180 views

On/off circuit using photo-resistor (LDR)

I am not afraid of the work but do not know how to do the math to calculate what I need for components. I am trying to create a photo resistor circuit to control some LED model street lights. I have ...
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44 views

Photoresistors detection

If I have a 2cm*2cm square and drill a really small hole in the middle thats barely visible for the human eye, and I place a photoresistor below , will the photoresistor be able to detect any light ...
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1answer
132 views

My previous theory was wrong, so why does this work?

Hi I am new to electronics, and I have made a light tripwire using an Arduino Uno. I made this on the idea that electricity follows the path of least resistance, which I now know to be false (http://...
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1answer
56 views

Having trouble with light activated circuit.

R1 = 10K 1/4W Resistor R2 = Photoresistor (any type) R3 = 2M2 1/4W Resistor R4 = 1M 1/4W Resistor C1= 10µF 25V Electrolytic Capacitor C2 = 100nF 63V Polyester Capacitor D1 = 1N4148 75V 150mA ...
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1answer
121 views

How can I use multiple Arduino-read photo resistors without interference between them? [closed]

I'm working on a prototype that utilizes a combination of photo resistors and LEDs to simulate a "tripwire" to detect when a coin falls through a clear tube. When using one tube, one photo resistor, ...
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4answers
208 views

How accurate is a photoresistor?

I'm doing a school project in which I need to measure the amount of light emitted by a specific object. The first thing that came to my mind was to use a photo resistor hooked up to a voltage meter ...
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2answers
341 views

how to reverse a photoresistor

Ive made up a laser security sytem that uses a pnp and npn transistor. Everything is going well except for the LDR. When there is no light the led will stay off. And once there is light it will turn ...
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1answer
90 views

deciphering schematic and diagnosing fault in cine camera circuit

I'm trying to understand part of this schematic in order to diagnose a fault with the light metering on an old (circa 1974) Nizo super 8 cine camera (other functionality appears to be ok). I ...
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2answers
461 views

What is RadioShack 276-0326?

It says it is an ambient light sensor, but is it a phototransistor? Something else? It has Vcc and Vout pins. Bonus points if you include a data sheet.
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1answer
69 views

How to delay the transistor turning on using a photoresistor?

I am a beginner in electronics, my project is the following: I am trying to build a simple circuit to switch on and off my garden lights according to the brightness level. More to the point, I'd like ...
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1answer
226 views

Photocell and Relay switch not working properly

I am trying to build a simple circuit to switch on and off my garden lights according to the brightness level. More to the point, I'd like the lights to turn on when it's dark and off in the morning. ...
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3answers
260 views

dimming led with photoresistor

I want to dim a led in a circuit if there's less light. However, the Photoresistor I'm working with reduces the resistance when there's more light. How can I achieve the opposite effect on resistance ?...
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3answers
808 views

How to avoid Relay buzzing noise? (LDR dependent)

I have the following circuit where I'm switching a relay based on whether it's day or night. I made a voltage divider using a pot and an LDR, which leads to the NPN transistor. So when it's dark the ...
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3answers
391 views

Violin bow position tracking with SMD LEDs and photoresistors

Objective: Marking labels indicating the positions of the violin bow on an acoustic signal, for example, a single musical note played by a full-length bow. The following video shows the example I am ...
3
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2answers
263 views

Component to detect the state of an external LED

I need to detect the state of an LED in a machine that I cannot connect to in any electrical way. So I would like to measure the light emitted from this LED. The conditions: The ambient lighting is ...
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2answers
182 views

light dependent 5V switch

I wired up this light dependent switch which works fine. when in daylight and covered. how can i make it work when the light source is dimmer? ie is it a case of changing 1 of the resistors?
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1answer
318 views

How to control a motor with a photoresistor

I have a little 2 to 5 volt hobby motor that I would like to control with a photoresistor aka photocell. What is the simplest way to control the circuit? Is there a photo resistor with enough range ...
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2answers
183 views

Night activated LEDs

I want to use a photo resistor to make a circuit like this But instead of light causing the led to turn on, I want darkness to cause the led to turn on.
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3answers
370 views

Separating Digital GND from Analog GND

I'm connecting CdS photoresitor and ADC (MCP3204) to the RPi. And MCP has DGND and AGND. I am about to connect both GNDs to the GND on RPi's GPIO, naively. Is that problematic if I want to read the ...
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1answer
2k views

Use a photoresistor to read an IR LED from an Itron energy meter

I want to read my meter at home with an Arduino board. My meter, an Itron C1S, has an IR emitter that pulses once (10ms width) every Wh. I want to know if it is theoretically possible to use a ...
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1answer
654 views

How can I detect when an LED changes color from red to green and quickly send a message to a PC to capture an image from a camera?

I am working with a 3rd party IR curtain system, and the only way to tell in real-time that something has pierced the curtain is an LED at the top of the sensor pole that changes from green to red ...
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1answer
69 views

Knowing the type of output signal

I have a digital photocell, where after dissembling, I see that it uses a ATMEGA88 chip(datasheet of the chip), but I do not have the schematic of the photocell. The whole photocell has only a pair ...
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2answers
3k views

What do Capacitors do in a System with a Speaker?

I made a circuit based on a diagram from my physics teacher. The circuit has a 555 chip connected to seven wires that make up a circuit. The circuit includes a photocell resistor that acts as a ...
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2answers
538 views

Are photoresistors reliable for light sensing applications?

I've used photoresistors for hobby projects before, such as this one: http://www.foxytronics.com/learn/electronics/kit-guides/starter-electronics-kit-guide/making-an-led-light-sensor However, now I'...
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177 views

How to light a LED using photo transistors output?

I built a circuit using RPR220 photo sensor to detect the surface displacement caused on a material when external force is applied. I could see the output on a CRO even when there are minute changes ...
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2answers
253 views

Simple circuit reacts to touching a node

I am trying to repeat a circuit from this post. For some reason it does not work properly, and trying to fix it I figure out strange behavior. LED turns on if I touch R3 with my finger or with ...
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1answer
128 views

circuit analysis of DC-source, inductance and modulated resistance

Here's an interesting problem. Consider a DC voltage source (for bias), an inductor (supply wires, for instance) and a resistor, which changes its resistance as a function of time: \$ R(t) = R_{offset}...
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1answer
974 views

Reversing a Photoresistor

I'm a total newbie at this, but I have a photoresistor set up so that it controls the shorting on an audio circuit. When light is on, it shorts and cuts the sound. When it is dark, it closes and ...
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1answer
1k views

How do I build a light-activated motor? [closed]

I'm trying to build a motor that is activated when light shines on a photoresistor/transistor (can anyone explain the difference?), but I'm totally lost right now. I can only utilize wires, batteries, ...
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2answers
411 views

Sensing Light Differences in Photo-Resistors

I'm planning to make a little device that detects when a path of laser light is broken. The device will have 3 photo-resistors and three corresponding lasers. Like so: ...
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2answers
11k views

Basic circuit to keep LED either on or off depending on night/day

How can I have a LED either on or off (not in between) depending on night or day with basic electronics? I have created the circuit below, but it only shines and in darkness it dims. The photo-...
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2answers
588 views

detect a change in state of voltage divider without using ADC

I am using a photoresistor for a laser trip wire setup to detect motion. I am a little short of adc channels here so would like to use a simple GPIO to read the state of the photoresistor ckt. I am ...
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3answers
899 views

Whats up with my photoresistors! (Wonky readings, non-stable, I'm missing something)

I'm working on a photoresistor array with my arduino, and I'm having a little trouble getting stable readings. I'm driving 7 rows one at a time with arduino's digitalWrite(pin,HIGH) command and ...
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2answers
1k views

How to name what this resistor is doing?

I have a basic circuit that uses a photoresistor powered by a five volt source. I had made this project to show my son about various sensors and had used a circuit I had found online. It looks ...
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3answers
1k views

Reading From a Large Array of Photoresistors

I'm an undergrad just starting to study Electrical Engineering. For the first hobby project I'm starting, I want to use a microcontroller to read analog voltage values from a very large array of ...
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2answers
398 views

Do LEDs Need UVLOs (Undervoltage-Lockouts)?

I'm currently working on a project involving (I think 3mm, 1.5VDC) Infrared LEDs. However, due to my photoresistor, I think the current, voltage, or whatever (forgot) will vary greatly to minuscule ...
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4k views

Zener Diode for Minimum Voltage Regulator

I forgot the name of it, but I remember one post where it said that you can use a zener diode as a "minimum voltage regulator". I don't think I used the right term for it, but here's what I'm doing. I'...
2
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2answers
2k views

I want to build an interactive LED Table. What are my options for a controller?

I have seen a couple of videos and instructables where people have created a matrix of LEDs controlled by photodiodes/photoresistors inside coffee tables, so that when you put your hand over the table ...
3
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2answers
501 views

Light detector linearity with varying wavelength

Given the same intensity of light, in varying wavelengths, which is typically more linear with their output: Cds (photo resistor) or a Photo transistor? I would assume that the junctions in the ...