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

learn more… | top users | synonyms

0
votes
2answers
116 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.
1
vote
3answers
110 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 ...
0
votes
1answer
393 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 ...
2
votes
1answer
192 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 ...
-1
votes
1answer
58 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 ...
1
vote
2answers
202 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 ...
4
votes
2answers
217 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 ...
0
votes
2answers
109 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 ...
1
vote
2answers
168 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 ...
0
votes
0answers
98 views

XBEE's w/ Photo-resistor isn't making LED change brightness?

Below is a circuit draw up of my configuration. My problem i'm having is my LED is not changing in brightness as fast as I wanted. It seems there is a huge delay and I want to know why this is. Below ...
2
votes
1answer
90 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) = ...
2
votes
1answer
243 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 ...
-4
votes
1answer
363 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, ...
0
votes
2answers
175 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: ...
5
votes
2answers
5k 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 ...
1
vote
2answers
394 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 ...
2
votes
3answers
595 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 ...
11
votes
2answers
878 views

Not sure 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 ...
1
vote
3answers
730 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 ...
1
vote
2answers
280 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 ...
-1
votes
3answers
2k 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. ...
2
votes
2answers
1k 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
votes
2answers
335 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 ...