LED project for 9 year old… suggestions?

For a class project my daughter wants to build a LED flashlight.

She is to create product that she will sell to her classmates. She must make 1 prototype and 20 to 25 units to sell.

She insists that it must be an LED flashlight. Cookies, cupcakes, brownies are out.

She will be making the prototype and the other 20 units! I'm only helping on design and teaching her how to solder. Oh and can't forget financing it (ouch but can't say no to her making a bunch of lights).

The problem is the COST of the components specifically the case for the light. It would be nice to use an Altoids or similar box or some type of tube type case. My hope is to keep total cost around or under $40.

Because of cost we are not going to have a switch. On/off will be connecting and disconnecting the battery. Run-time should be plenty long.

Please share ideas on how to keep the cost as low as possible! :thinking:

The planned design and estimated cost per component is in the next post.

Thanks,


Shawn

Design:
Her current plan is to build something similar to the following but in a case:


Parts:
Hot glue to incase the resistor and LED leads. (open to suggestions here)
1 9volt battery ($1.00 each if bought in bulk)
1 snap connector for 9volt ($0.60)
1 resistor (? … I already have enough… I think)
1 5mm LED ($0.20 assorted bulk pack from Radio Shack)
1 Case. ($$$) This a problem as I haven't found anything cheep.

Cost: $1.80 + case($2-$4) puts me over the $40 mark. I'm ok being over 40 but all of the cases that I have found put me significantly over.


Specs on the LED:
LED (Red) Package: 5mm & 3mm Vf: 2.1V
LED (Green) Package: 5mm & 3mm Vf: 3.2V
LED (Yellow) Package: 5mm & 3mm Vf: 2.2V
LED (Clear/Amber Out) Package: 5mm Vf: 2.2V

[FONT=&quot]My plan is to run off a 9v and ~ 700 resistor so they will be running around 10ma.

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I wouldn't use 9V batteries since more than 70% of the energy will be wasted in the resistor.

Kind of being rushed out the door here, but a quick idea: PVC water piping for the flashlight body. Haven't thought how you could wire it yet though. You could also just get a bunch of 2x aa battery carriers and either have those be the body or put them in something like a PVC tube. Good luck to you and your kiddo!

_Shawn_ said:

For a class project my daughter wants to build a LED flashlight.

She insists that it must be an LED flashlight. Cookies, cupcakes, brownies are out.

Because of cost we are not going to have a switch. On/off will be connecting and disconnecting the battery. Run-time should be plenty long.

Shawn

Click to expand...

Anything with flexible sides allows a "switch". The photon light is a good example. If you buy a bunch of the cheap ones you will have batteries and LEDs for less than a buck each.
Screw on "switches" also cost nothing.

The idea of a one shot emergency light sort of fits her idea. Button cells, a LED, and a pull strip that turned the light on when pulled out would be easy to build. A while back people were making these without the strip and attaching them to buildings etc, just for fun.

Again, not a flashlight but I just bought 50 LEDs with resistors for about $10.00 and they run at 12-15 volts. On a piece of wire and hooked to a cigarette lighter plug they might prove handy.

The evil part of me says to get her a kit that emulates the sound of a cricket. She learns to solder and if her teacher gives her an A she shows where it is hidden in the class room.

I was thinking about using some copper pipe or possibly galvanized. The only problem with the PVC pipe is the wiring.


As for using a flexible case as a switch, had not thought about that one.


Good ideas....


The cricket, I've been wanting to get one of those for a long time. Now I can do it and say it's for the kids.

Hi, perhaps:
- 2 x AA alkaline batteries in one of those 2 cell battery holders
- 1 or 2 (in parallel) each 5mm red or red / orange LED hot glued to the end of the holder
- Small switch from cherry semi or similar

I made a case one time from tape. Wrap it carefully with some thick Al tape, then top it off with a colored tape, such as the mylar film that is used on model airplanes. You can get it in quite a variety of colors, and surprisingly, it looks pretty decent when finished.

With 5mm size LEDs and 2 alkalines, they will run for a very long time, so don't worry about battery replacement.

Sounds like a great father / daughter project you have there.

BTW - get some solder paste for the soldering work - it is so much easier to work with than wire solder.

Harry

edit - I forgot to mention - when you make the case from Al tape, first make it into a triple layer thickness, then put it onto the shape. This makes it lay down with fewer wrinkles.