Simple Light Sensor

Discussion in 'The Projects Forum' started by grplnxprt, Jun 6, 2015.

  1. grplnxprt

    Thread Starter New Member

    Jun 6, 2015
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    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.
     
  2. cornishlad

    Member

    Jul 31, 2013
    196
    25
    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)
     
  3. grplnxprt

    Thread Starter New Member

    Jun 6, 2015
    9
    0
    Thanks for the reply.

    Just tried it. Same thing.

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

    Administrator

    Apr 5, 2008
    15,649
    2,348
    Hello,

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

    Bertus
     
  5. grplnxprt

    Thread Starter New Member

    Jun 6, 2015
    9
    0
    I just realized that I was using 2 AAA batteries before also.

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

    Thread Starter New Member

    Jun 6, 2015
    9
    0
    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.
     
  7. grplnxprt

    Thread Starter New Member

    Jun 6, 2015
    9
    0
    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.
     
  8. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,176
    397
    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
     
  9. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    With a comparator you can make LED light at any selected light level.
     
  10. grplnxprt

    Thread Starter New Member

    Jun 6, 2015
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    0
    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?
     
  11. grplnxprt

    Thread Starter New Member

    Jun 6, 2015
    9
    0
    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.
     
  12. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,176
    397
    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.
     
  13. grplnxprt

    Thread Starter New Member

    Jun 6, 2015
    9
    0
    Thanks Bernard. I'll read about comparators.
     
  14. bertus

    Administrator

    Apr 5, 2008
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  15. cornishlad

    Member

    Jul 31, 2013
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  16. RodneyB

    Active Member

    Apr 28, 2012
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  17. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    What is the Radio Shack "ambient light sensor"? Part number, physical description, anything...

    ak
     
  18. grplnxprt

    Thread Starter New Member

    Jun 6, 2015
    9
    0
    cornishlad - Thanks. I'll check it out,

    RodneyB - Thanks. I'll check it out.

    AnalogKid -
    • Model: 2760325
    • Catalog #: 2760325
    RADIOSHACK® 3MM AMBIENT LIGHT SENSORS
     
  19. upand_at_them

    Active Member

    May 15, 2010
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    It's a phototransistor.
     
  20. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,395
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    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.
     
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