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 Dark detector with white LED
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By: gleasone (offline) on Monday, March 21 2011 @ 01:47 PM PDT  
gleasone

Awesome!!! Thanks for the fact and opinion! After reading your opinion, you're probably right about not getting much gain out of it. Maybe I'll skip the white led on the bot... But, knowing that it will work like I wanted it to, I can still use it on other projects. Thanks for your help and your patience with me, I appreciate it very much!


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By: Anonymous: Grainne () on Friday, March 25 2011 @ 09:45 AM PDT  
Anonymous: Grainne

Hi there,

First I'd like to tell you how much fun I've been having trying out these experiments for myself, love this site!

I was wondering if you would be so kind as to help me make a calculation. I am trying to modify the circuit to suit a 9V power supply, and so far I have been able to get my yellow LEDs working nicely with it and the other components mentioned in your instructions.

However, when I try to connect a white LED (with typ. forward V 3.2) the LED shows no sensitivity and just lights up. I've tried using resistor calculators online but to no avail. It calculated that a 220ohm resistor would work but I get the same result. I'm sure I'm leaving some important part of the equation out, but I can't figure it out.

I would really appreciate your input, this is driving me crazy!

Have a good weekend Smile

Grainne






       
   
By: Windell (offline) on Friday, March 25 2011 @ 09:50 AM PDT  
Windell

I was wondering if you would be so kind as to help me make a calculation. I am trying to modify the circuit to suit a 9V power supply, and so far I have been able to get my yellow LEDs working nicely with it and the other components mentioned in your instructions.

The circuit that we've discussed here does *not* work with 9 V. That rather suggests that you've modified the circuit somehow... and you haven't said how. That leaves me rather helpless to guess what the problem might be.


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By: Anonymous: gleasone () on Friday, March 25 2011 @ 01:57 PM PDT  
Anonymous: gleasone

As Windell discussed on page 1 of this discussion, try lowering your input voltage down to 3.5 - 4 volts (3 - AAA batteries in a series). Use the original schematic he posted and add the current limiting resistor (for the white led). That should make the white led work with the circuit as intended.

**Sorry Windell, not trying to step on any toes... Smile**





       
   



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