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Damsel in distress

 
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lochnessie233
Semi Newbie


Joined: 22 Feb 2007
Posts: 6

PostPosted: Thu Feb 22, 2007 8:24 am    Post subject: Damsel in distress Reply with quote

Hello one and all!

I am a product design student at university and our latest project requires us to make a working prototype of a battery-powered light. I have chosen to use LEDs but am not sure where to buy them, if i need a kit, if i will have to wire it all myself, or how to work it.

I have never worked with electronics before so the most straightforward option would be great. I simply want a small (has to be under 70mm by 70mm wide and less than 20mm tall) white or cream coloured LED light that attaches to a battery pack. Ideally the device will turn on and off by pressing against the material (a soft rubber) at one spot with a clicking button. What kind of batteries should I use? Do you know of any kits that I can buy to ease my troubles? Any and all advice is appreciated! Thanks so much!

Vanessa
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BronzeG3
HG Master


Joined: 30 Apr 2006
Posts: 134

PostPosted: Thu Feb 22, 2007 9:11 am    Post subject: Reply with quote

You can get LED's here.

What kind of battery pack are you using? You will need a resistor to limit current, and that depends on the voltage being supplied by the batteries.
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lochnessie233
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Joined: 22 Feb 2007
Posts: 6

PostPosted: Thu Feb 22, 2007 10:56 am    Post subject: Reply with quote

Hey,

It is a relatively small bedside lamp/nightlight so I want it to have a nice glow. I am open minded about what kind of batteries I use. What do you suggest? How high of a current will I need for such a small light?
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Nginuity
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Joined: 13 Nov 2006
Posts: 224
Location: Dallas, Texas

PostPosted: Thu Feb 22, 2007 5:20 pm    Post subject: Reply with quote

lochnessie233 wrote:
Hey,

It is a relatively small bedside lamp/nightlight so I want it to have a nice glow. I am open minded about what kind of batteries I use. What do you suggest? How high of a current will I need for such a small light?


Hello. if you are only powering one superbright LED, like, say this one for instance:
http://alan-parekh.vstore.ca/product_info.php/products_id/29

It allows voltage operation at 3.4 volts and the current draw is 30mA. Three AA batteries in series should give you 4.5 volts. That is what I would use. Others may use something different.

For the current limiting resistor, you would need to calculate the value. You can do so with this calculator if you don't want to bother with the math:

http://alan-parekh.com/led_resistor_calculator.html

According to the calculator, you need to put a 39 ohm resistor in the circuit before you connect the LED.
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lochnessie233
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Joined: 22 Feb 2007
Posts: 6

PostPosted: Fri Feb 23, 2007 3:23 am    Post subject: Reply with quote

Thanks for your advice!

Any ideas on how to make the light activated by squeezing it?
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BronzeG3
HG Master


Joined: 30 Apr 2006
Posts: 134

PostPosted: Fri Feb 23, 2007 3:38 am    Post subject: Reply with quote

I think that depends on what kind of case you are putting it in. You could mount a toggle button in a cardboard tube, decoarte the tube, and when you squeze the tube, it hits the switch and toggles the lights on and off.
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Nginuity
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Joined: 13 Nov 2006
Posts: 224
Location: Dallas, Texas

PostPosted: Fri Feb 23, 2007 5:23 pm    Post subject: Reply with quote

BronzeG3 wrote:
I think that depends on what kind of case you are putting it in. You could mount a toggle button in a cardboard tube, decoarte the tube, and when you squeze the tube, it hits the switch and toggles the lights on and off.


Or, take a pushbutton switch that is normally open, and put it inside of a hollow rubber ball.
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lochnessie233
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Joined: 22 Feb 2007
Posts: 6

PostPosted: Tue Mar 06, 2007 6:12 am    Post subject: Reply with quote

Okay! I figured out how to encase the lighting so it doesn't break, and how to activate it but here is my problem.

I purchased the Spoka light from IKEA and took it apart. I bought four LEDs with a typical voltage of 3.5, if=20mA, up to 5 V http://www.maplin.co.uk/Media/PDFs/n21by.pdf (spec sheet for LEDs). Now the batteries I'm using are 3 AAA's with a voltage of 3.6.

first, is it possible to unsolder the old LEDs in it and add my new ones? How do i go about that?

secondly, if not-- then what kind of a circuit board do i need? resistor? can i reuse the batteries or should i swap them out for another kind? Please help me. I am a complete amateur so I beg of you to talk in layman's terms.

i would appreciate if you should show me the order to hook it up in as well, if i am not able to use 'Spoka'. Thanks so much!
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Nginuity
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Joined: 13 Nov 2006
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Location: Dallas, Texas

PostPosted: Tue Mar 06, 2007 8:00 am    Post subject: Reply with quote

To unsolder the led's, go get some copper braided solder wick, or use a solder sucker. If you get it from an electronics supply store, they will know what you are asking for.

Here is an article on how to desolder: http://www.aaroncake.net/electronics/desolder.htm

Using 4 LED's in parallel, you will need a 1 ohm (1/4 watt) resistor coming from the positive side of the battery, to the anode side of the LEDs (The round side, not the flat side). Then connect the flat side (cathodes) of the LED's together and connect that to the negative side of your battery pack.

Oh, I forgot, your switch. Add it in between your connection from the diodes cathode (flat side) to battery negative.
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lochnessie233
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Joined: 22 Feb 2007
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PostPosted: Tue Mar 06, 2007 8:43 am    Post subject: Reply with quote

Thanks so much for your help! That was really useful. Is that assuming I keep a 3.6 v battery(ies)? can i use a single, flat, round 3.6 v battery instead? also does it matter what size/amount of circuit boards i use? thanks!
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Nginuity
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Joined: 13 Nov 2006
Posts: 224
Location: Dallas, Texas

PostPosted: Tue Mar 06, 2007 11:01 am    Post subject: Reply with quote

lochnessie233 wrote:
Thanks so much for your help! That was really useful. Is that assuming I keep a 3.6 v battery(ies)? can i use a single, flat, round 3.6 v battery instead? also does it matter what size/amount of circuit boards i use? thanks!


That calculation should apply to any 3.6 volt battery. This means that as long as you have 3.6 volts between the + and -, it will work as designed. And yes, you can use the little 3.6v round flat battery, the CR2032, but it will severely cut down on the amount of time you will get out of the light.
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Alan
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Joined: 29 Jan 2006
Posts: 1399
Location: Winnipeg, MB

PostPosted: Tue Mar 06, 2007 11:56 pm    Post subject: Reply with quote

lochnessie233 wrote:
I purchased the Spoka light from IKEA and took it apart. I bought four LEDs with a typical voltage of 3.5, if=20mA, up to 5 V http://www.maplin.co.uk/Media/PDFs/n21by.pdf (spec sheet for LEDs). Now the batteries I'm using are 3 AAA's with a voltage of 3.6.


Sounds like a great project! I wonder if those batteries are not quite fully charged. If they are all in series it should be close to 4.5 Volts.
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lochnessie233
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Joined: 22 Feb 2007
Posts: 6

PostPosted: Wed Mar 07, 2007 3:06 am    Post subject: Reply with quote

actually, yes, it is a rechargable battery set. their is a plug for the light that is 4.8V, but I will be using it mainly on battery power. Will it short-circuit if I change the LEDs to 3.5v each (4) and plug it in?
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Alan
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Joined: 29 Jan 2006
Posts: 1399
Location: Winnipeg, MB

PostPosted: Wed Mar 07, 2007 8:46 am    Post subject: Reply with quote

lochnessie233 wrote:
actually, yes, it is a rechargable battery set. their is a plug for the light that is 4.8V, but I will be using it mainly on battery power. Will it short-circuit if I change the LEDs to 3.5v each (4) and plug it in?


Design the current limiting for a supply voltage of 5 volts and you should be fine.
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