I'm trying to make a simple light sensor. Just a AAA battery, a 5mm LED, and light sensor.

I bought some ambient light sensors from Radio Shack and made it work.

I bought some LDRs online and it's not working with one of them in place of the ambient light sensor.

The LED I'm using:
"E-Projects - Clear Yellow / Amber 5mm LED - Wide Angle Light"
Clear Yellow/Amber 5mm LEDs - Wide Angle Light
Max Current: 20mA
Forward Voltage: 1.8 - 2.1
Max Reverse Current: 10mA
Power Angle (deg): 160 - 180
MCD: 4000 - 5000

The LDR I'm using:
"Photo Light Sensitive Resistor Photoresistor Optoresistor 5mm GM55399 5539"
Maximum Voltage: 150 Volt DC
Maximum Wattage: 100mW
Operating Temperature: -30 ~ +70 deg C
Spectral Peak: 540nm
Light Resistance (10 Lux): 50-100 Kohm

The battery I'm using:
Radio Shack AAA

Again, it worked with a 5mm ambient light sensor I bought from Radio Shack, but not with the LDR.

I watched a video of somebody doing this, but his LDR was bigger than mine.

I'm completely new to this. If I'm leaving out important information, please let me know.

I'm open to using any other suggested components. I just need the LED to turn on when light hits the sensor and turn off when the sensor is covered.

Any help is greatly appreciated. Thank.

 

Forward Voltage: 1.8 - 2.1

Radio Shack AAA
[/QUOTE]
I'm a bit surprised the led light at all with only 1.5v.
Try again with 2 x aaa (3v)

 

Thanks for the reply.

Just tried it. Same thing.

Works with the ambient light sensor, but not with the LDR.

 

Hello,

Can you provide a schematic of the current set-up?
You can upload a schematic using the "Upload a File" button.

Bertus

 

I just realized that I was using 2 AAA batteries before also.

You're right. One battery won't light the LED.

 

Bertus, I tried figuring out how to draw a schematic. I'm afraid it's a bit over my head at this point.

I can describe it and hope that works. It's pretty basic.


Battery positive goes to light sensor.
Light sensor goes to LED.
LED goes to battery negative.

When the light sensor is the ambient light sensor it works.
When I substitute the LDR in it's place, it doesn't work.

I hope this helps.

 

Alright...

I bought a 9v battery and a resistor.

I hooked them up and got the LDR to light.

But, it behaves just like the ambient light sensor.

It's brighter depending on the amount of light present.

I want the LED 100% on when there is light and 100% off when there isn't.

Anybody?

Thanks again.

 

Can you measure your LDR with different light conditions. Different LDRs vary wildly in specs.
Examples: Bright window, ambient, & dark,
2k, 10k, 1M
7k, 38k, 1M
50, 130, 10k
1.2k 7k, 200k

 

With a comparator you can make LED light at any selected light level.

 

Bernard,

I had to Google how to measure it. It says to use a multimeter. I don't have a multimeter. I can gain access to one Monday.

Is there a certain measurement I'm hoping for? If so, can I just find LDRs online that fit that criteria and buy them?

 

Thanks for all the replies.

What I'd really like is for somebody to tell me in laymen's terms how to make this.

I need a simple circuit that fully lights an LED when there is light present and turns it off when there isn't.

The simpler, the better.

 

With comparator, just about any LDR will work; with a choice , would pick a mid range around 10k. LM393N is fairly common if available to you.It is late, back Monday.

 

Thanks Bernard. I'll read about comparators.

 

Hello,

On this page of the EDUCYPEDIA you will find some circuits for light sensors:
http://educypedia.karadimov.info/electronics/circuitssensorslight.htm

Bertus

 

here's some good info on the topic.
http://www.bristolwatch.com/ele/vc.htm

 

Please see this thread http://forum.allaboutcircuits.com/threads/741-problem-in-light-sensitive-switch.107306/ it uses a comparator and 12 volt battery but it does work. Not my original post but the one Mike helped me with.

 

What is the Radio Shack "ambient light sensor"? Part number, physical description, anything...

ak

 

cornishlad - Thanks. I'll check it out,

RodneyB - Thanks. I'll check it out.

AnalogKid -

• Model: 2760325
  
• Catalog #: 2760325

RADIOSHACK® 3MM AMBIENT LIGHT SENSORS

 

It's a phototransistor.

 

If you go thru the user's comments on RS site someone linked to the data sheet. It's an Everlight ALS-PTP144-6C/L451. At first glance it is not suitable for this project as it will only pass a few milliamps at full brightness when there is 5V across it.

Seems the good old CDs cells are now banned by the ROHS directives. I don't have any good alternatives to offer that you can get at Radio Shack.