Need help with a Cub Scout project

Dave H

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Aug 6, 2009
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I am a webelos den leader and one of the things we need to complete for the engineering pin is to construct a simple working electrical circuit using a flashlight battery switch and light. I always like to go above and beyond. I would like each boy (8) to build their own flashlight. I would love for each boy to their own quality flashlight but the budget gets in the way. I was looking at components on DX but not really satisfied with what I found. I saw on ebay I could buy some cheap single AA battery flashlights for about a dollar a piece. I was wondering if I bought those ripped out the cheap led and replaced with a higher quality LED. Is that possible? The boys have soildered before. It would be awesome if we could add a two mode driver. Any advice on where I can get inexpensive materials and just how much I can do? I am trying to keep the flashlights in the $5 to $10 price range each. Any advice would be greatly appreciated.
 

wyager

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Great idea! I can't really help much as I have never DIY'd a light, but your best bet might just be to take apart a bunch of cheap-o DX lights and have them learn what all the parts do and put them back together again.
 

AnAppleSnail

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To keep it within that cost AND be a built-from-scratch light, you might have to go with a 5mm LED over a power LED. Those are plenty for working in the dark. You'll have them making a Cub-Paklite, powered by a 9v battery. For real fun, add glow-powder on the epoxy so that you can find the things when they get set down.

I'm suggesting a 9v battery because voltage-boosting electronics are, at cheapest, just under $2 apiece. I'll talk about a voltage-boosting design later.

LED: You might go with Super Bright LEDs (the 5mm ones from Sparkfun worked well for a project here) because these are cheap, and just give each Scout up to two for his light. If you want power LEDs, you get into needing heatsinking and stuff.

Get a pack of resistors
Buy a 9v battery connector for each. (Radio shack has these, at least)
Get a little slider switch for each - a "Single Pole Double Throw" gives 2 settings (and Off). Rocker switches are easier to waterproof.
Get some of those LEDs.
Each scout will be making a 2-speed light by choosing 1 or 2 LEDs, and a resistor value for each mode. To calculate how bright the LEDs will be, you need to know the current. That's calculated like this:

Battery voltage = (all LED Forward Voltages) + Resistor Voltage
9v = (about 3.2v per LED) + (resistor value) * current in amps
9v - 2*3.2v = resistor*current

A 5 ohm resistor would give
2.6v = 5*current
current = .52 amps

For a 5mm LED this is way too high - you want them down at 0.03 amps (30 milli-amps) - resistor values around 90 ohms are good for 'high,' and around 100 times that for 'low.'

Once wired, you can put epoxy on the wires, 9v plug, LEDs, and switch body. Glow powder in the epoxy will charge from sunlight and the LEDs. Once this is stuck on a 9v battery it'll run for a looong time. The 9v connection might rust, but getting wet won't hurt it too much as water isn't usually very conductive. A slide switch will self-clean as long as it doesn't get stuck.


=====================================================================
Power LED flashlight.
Needs power LED
Voltage-boosting driver
Heatsinking
Switch
A reflector or optic is nice



For a power LED light you'll probably want a voltage-boosting circuit. This is one I've used in a helmet light: I have in mind for you. It won't deliver a lot of current, but that's ok - 200 mA is plenty for a flashlight. This one is single-mode, but there are other options, like You wire the outside ring to battery (-), perhaps the flashlight tube; and the nub on the front of the battery goes to the middle circle.

With power LEDs comes the need for heatsinking. If you can't get metal bodies on the lights donated or cheap from some local metal shop, you can always use a half-inch copper pipe end cap for a metal head. This'll work well with a PVC battery tube, although I'm not sure how well you can bond the two together. You'll need to drill one or two holes in the end cap for the LED's wires. Thermal epoxy will make the LED give its heat to the copper, and the end cap will hold a reflector or optic nicely.

You'll need a place for the LED to sit, a spot for the driver (The top of the battery tube near the LED works best), and a way to hold the battery and switch the driver off and on. Never connect an LED to a powered driver.

I'll add some diagrams so you can see what I'm talking about.



Drivers: Look for ones like these (DX used because they have many things, not because they are good). Cheap LED drivers will usually have more power with higher voltage. That also means that as the batteries die, the lights will get dimmer and draw less power, so it lasts a bit longer. Also, adding a resistor between the driver and the battery makes a handy 'low' mode on single-mode drivers.

[url=http://www.dealextreme.com/details.dx/sku.4451]1.5v, 300 mA single-mode

1.5-4.2v ~200 mA single-mode
1.5-4.2v ~600 mA single-mode
 

Nedtheshred

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Nov 23, 2004
Messages
221
Location
California
To keep it within that cost AND be a built-from-scratch light, you might have to go with a 5mm LED over a power LED. Those are plenty for working in the dark. You'll have them making a Cub-Paklite, powered by a 9v battery. For real fun, add glow-powder on the epoxy so that you can find the things when they get set down.

I'm suggesting a 9v battery because voltage-boosting electronics are, at cheapest, just under $2 apiece. I'll talk about a voltage-boosting design later.

LED: You might go with Super Bright LEDs (the 5mm ones from Sparkfun worked well for a project here) because these are cheap, and just give each Scout up to two for his light. If you want power LEDs, you get into needing heatsinking and stuff.

Get a pack of resistors
Buy a 9v battery connector for each. (Radio shack has these, at least)
Get a little slider switch for each - a "Single Pole Double Throw" gives 2 settings (and Off). Rocker switches are easier to waterproof.
Get some of those LEDs.
Each scout will be making a 2-speed light by choosing 1 or 2 LEDs, and a resistor value for each mode. To calculate how bright the LEDs will be, you need to know the current. That's calculated like this:

Battery voltage = (all LED Forward Voltages) + Resistor Voltage
9v = (about 3.2v per LED) + (resistor value) * current in amps
9v - 2*3.2v = resistor*current

A 5 ohm resistor would give
2.6v = 5*current
current = .52 amps

For a 5mm LED this is way too high - you want them down at 0.03 amps (30 milli-amps) - resistor values around 90 ohms are good for 'high,' and around 100 times that for 'low.'

Once wired, you can put epoxy on the wires, 9v plug, LEDs, and switch body. Glow powder in the epoxy will charge from sunlight and the LEDs. Once this is stuck on a 9v battery it'll run for a looong time. The 9v connection might rust, but getting wet won't hurt it too much as water isn't usually very conductive. A slide switch will self-clean as long as it doesn't get stuck.


=====================================================================
Power LED flashlight.
Needs power LED
Voltage-boosting driver
Heatsinking
Switch
A reflector or optic is nice



For a power LED light you'll probably want a voltage-boosting circuit. This is one I've used in a helmet light: I have in mind for you. It won't deliver a lot of current, but that's ok - 200 mA is plenty for a flashlight. This one is single-mode, but there are other options, like You wire the outside ring to battery (-), perhaps the flashlight tube; and the nub on the front of the battery goes to the middle circle.

With power LEDs comes the need for heatsinking. If you can't get metal bodies on the lights donated or cheap from some local metal shop, you can always use a half-inch copper pipe end cap for a metal head. This'll work well with a PVC battery tube, although I'm not sure how well you can bond the two together. You'll need to drill one or two holes in the end cap for the LED's wires. Thermal epoxy will make the LED give its heat to the copper, and the end cap will hold a reflector or optic nicely.

You'll need a place for the LED to sit, a spot for the driver (The top of the battery tube near the LED works best), and a way to hold the battery and switch the driver off and on. Never connect an LED to a powered driver.

I'll add some diagrams so you can see what I'm talking about.



Drivers: Look for ones like these (DX used because they have many things, not because they are good). Cheap LED drivers will usually have more power with higher voltage. That also means that as the batteries die, the lights will get dimmer and draw less power, so it lasts a bit longer. Also, adding a resistor between the driver and the battery makes a handy 'low' mode on single-mode drivers.

[url=http://www.dealextreme.com/details.dx/sku.4451]1.5v, 300 mA single-mode

1.5-4.2v ~200 mA single-mode
1.5-4.2v ~600 mA single-mode

Very nice advice and info, love that photo also
 

AnAppleSnail

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Joined
Aug 21, 2009
Messages
4,200
Location
South Hill, VA
Here's a vague diagram. I forgot to note that the green strip is the LED constant-current driver you pick. The wires included with the DX ones go to the LED + and -.

The Cree XR-E is very easy to solder to. Luxeons are hard. Generally you want nice large solder pads.

4981267465_ffcca2db29_o.png


Clear as mud? If I've lost you, let me know if you're interested in hearing more.
 

PCC

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Messages
2,326
Location
Sitting' on the dock o' The Bay...
You can cut costs on a 9V battery flashlight by digging through the battery recycle bins at work and digging out the 9V batteries. I do this and salvage the card with the connectors. Radio Shack sells these but they cost more if you buy them there. The ones that I make are really simple designs with four parts: two 5mm LEDs, one resistor, and one connector. No switch is needed as you can hang the unit onto one side of a 9V battery when not needed then swing it around to make contact to turn it on for momentary use. For constant on just clip it on. I use 2-ton epoxy with glow powder to pot the circuitry to make it more reliable.

Tektite sells a flashlight kit that includes everything needed to assemble a working LED flashlight. They have two different versions of the same light: one that is easy to assemble and one that requires soldering. The one that requires soldering is cheaper, too. http://www.tek-tite.com/src/products.php?c=2245
 

Dave H

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Joined
Aug 6, 2009
Messages
56
Thanks for the advice. I'm not sure about the 9 volt battery though. What sort of casing can I use for that? Also as mentioned quality 9 volt batteries can get expensive. I would prefer to stick with AAs just because they are common and cheap even for fairly high quality ones. I see on ebay I can get a noname single AA LED flashlight with an aluminum shell for about $1.50. Not sure if I can post links to ebay http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=280442891750&ssPageName=STRK:MEWAX:IT
I was thinking if I started with that I could add a driver and possibly heat sinking and upgrade the LED. I also found a an Ultrafire sigle AA for $7. I thought if I purchased 10 I could probably get 8 to work. I could just disassemble them then have the boys reassemble their own.

Any thoughts and or advice?
 

wyager

Flashlight Enthusiast
Joined
Feb 10, 2010
Messages
1,114
I was thinking if I started with that I could add a driver and possibly heat sinking and upgrade the LED. I also found a an Ultrafire sigle AA for $7. I thought if I purchased 10 I could probably get 8 to work. I could just disassemble them then have the boys reassemble their own.

Any thoughts and or advice?

This is what I would do. How much you want to disassemble them is up to you, you could go as far as removing the LED if you wanted, but I think it would probably make more sense just to unscrew everything and take out all the o-rings.
 

AnAppleSnail

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Joined
Aug 21, 2009
Messages
4,200
Location
South Hill, VA
Thanks for the advice. I'm not sure about the 9 volt battery though. What sort of casing can I use for that? Also as mentioned quality 9 volt batteries can get expensive. I would prefer to stick with AAs just because they are common and cheap even for fairly high quality ones. I see on ebay I can get a noname single AA LED flashlight with an aluminum shell for about $1.50. Not sure if I can post links to ebay http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=280442891750&ssPageName=STRK:MEWAX:IT
I was thinking if I started with that I could add a driver and possibly heat sinking and upgrade the LED. I also found a an Ultrafire sigle AA for $7. I thought if I purchased 10 I could probably get 8 to work. I could just disassemble them then have the boys reassemble their own.

Any thoughts and or advice?

With little 5mm LEDs (plenty for working in the dark), the 9v battery will last quite a while, especially with use of the 'low' setting. But they'd be more appropriate for in-tent lights than trail lighting.

Generally, any 1-AA LED flashlight already has a driver. Now, there's no telling how well the driver will work. As long as it gets the right voltage in it'll put some kind of power out that won't toast a power LED. And as long as the power LED has heatsinking it'll do its glowy thing.

I find that drivers make electronic design of flashlights extremely plug-n-play. With the last homebuilt light project I did, I added a switch for Off/Low/High, using a resistor to hobble the driver's power input. Partly because I like dim lights, partly because it would be boring otherwise.
 

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