Electrical Engineering Stack Exchange
Electrical Engineering Stack Exchange

Questions tagged [ldr]

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

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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 unit lux and is not equal to lux. TL;DR: How can…
Niklas E.
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Plugging a LDR into GPIO pins of a Raspberry Pi

I want to connect a LDR into the GPIO pins of my Raspberry Pi, I know that Raspberry Pi doesn't have an analog-to-digital converter so what I want to do is to signal a HIGH signal (3.3v) on the GPIO when there is low resistance on the LDR (something…
Tarantula
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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 little, so they're not as bright. The…
polemon
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Will there be any effects on a signal in a long wire?

I am going to need a large length of wire from my microcontroller analogue input to a LDR or similar sensor. The length of wire is likely to be about 100m so will it have any affects on the reading the ADC? Is there anyway I can reduce the effects?
Dean
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Please help me understand the following light-controlled relay circuit

I used the following circuit to control the outdoor light, and it works as I wanted. I am trying to understand the circuit and it looks like a comparator circuit, but I don't understand the use of 100 kOhm feedback resistor. Also how to choose the…
vtc
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Why use a pull-down resistor with a LDR and microcontroller?

I am looking at this: http://learn.adafruit.com/photocells/using-a-photocell It's connecting VCC <-> LDR <-> resistor <-> GND. And the analog input is between the LDR and the resistor. I understand than a resistor may be necessary to control the…
Weboide
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How to interface LDR with microcontroller?

I need to interface an LDR with a microcontroller. While searching for some circuit ideas on the internet, I came across two different ideas: One was using a voltage divider circuit with another resistor and input that into the ADC port of a…
gopal
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measuring time between extremely fast laser beam breakage using LDRs

I am conducting a scientific experiment to approximately measure the entering velocity and the leaving velocity of a magnet through an electromagnetic coil. Beside the coil are two lasers and two LDRs as depicted by the figure below. I expected this…
Denis
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Does an LDR age?

I have had a twilight switch lying in my basement for 5 years after it was used in my garden for about 5 years. This week I took it apart to convert it for (solar) use from 230VAC to 12VDC. What is left (for sake of this discussion) is a resistive…
jippie
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Relay? No clue how to breadboard?

I've got a circuit diagram I'm working from, this one: And I'm currently trying to breadboard it, as seen here: I've been trying to search google on how to wire a Relay, and am not yielding any viable results. I've got a omron 5VDC with 5 pins, 2…
John B
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What colors or wavelengths are photoresistors sensitive to?

Using an LDR or photoresistor, are they more sensitive to one color or wavelength compared to another, or are they consistent with any light? Why?
Passerby
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12v LED Strip Lights controlled by PIR *Want to add LDR to project*

I want to add an LDR (Light Dependent Resistor) to my Motion activated stair lights, then On/Off switch can be removed as well as the single Led (On Indicator Only) from my project (I want the LDR to control the On/Off). This is basically the first…
Ridach
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7555 timer replacement

I want to build this circuit but I do not have a 7555 low power timer so wondered if I can use a NE555? Also can I use a 2N2222 trasistor instead of a BC108? I don't want to try and build it without making sure I won't damage some components. Here…
Andrija Andrijašević
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Designing an op-amp circuit to generate a digital pulse from LDR

I am trying to design an op-amp circuit to generate a digital pulse when an LDR is quickly obscured from ambient light (like when you pass your hand over it). This is the circuit I built - a differentiator: And here is the output when I pass my…
M-V
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How do I control the sensitivity range of an LDR-controlled LED?

I'm trying to make an LED dim according to the ambient light (darker ambient -> brighter LED), through use of an LDR. I'm using a voltage divider with an NPN transistor (BUL38D). I've tried multiple values for each of the resistors shown, but always…
Guilherme Gaspar
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