What? A flashlight? What does that have to do with rocketry? Nothing! Our first construction project is simple, on purpose. More complex, rocket-applicable ones are coming. The LEDlite will ease beginners into working with electronic parts and soldering, AND yield a useful, novel item as well.
Up to the 1970's, thousands of people enjoyed electronics tinkering...ham radio, kitbuilding, and circuit hacking. The advent of the PC (about 1980) killed Heathkit (the largest kit maker) by creating a new "soft-ware hobby" for Techies. The number of electronic hobbyists today is probably 15% of what it used to be. BUT, it's coming back! People are getting tired of playing PC games and cruising the Internet...some yearn for the good old days of tube audio amps, and "homebrew" equipment. The Robot Wars has created an army of electromechanical hackers who are also hip to embedded controllers! Fire-fighting and Sumo wrestler robots are also in vogue.
The LEDlite uses 3 white LEDs running on 3 AA alkaline cells. Very high in efficiency, with an almost unlimited life, these LEDs output pure white light. For comparison, a $1 Chinese flashlight that also uses 3 AA cells was tested. It ran for 4 hours before depleting the alkaline cells. The bulb uses 0.5 Amps. It was 2 or 3 times brighter than the LEDlite, but the battery life is 10 times shorter
White LED's run at 3.6V, 30mA. Three AA cells in series provide 4.5V. So, a 27 ohm, 1/4W resistor will be put in series with each LED. The calculation is R = E/I = (4.5V - 3.6V) / 0.03A. If you plan on using NIMH (Nickle Metal Hydride) rechargable cells that are 1.2V each, use 15 ohm resistors instead of 27 ohm
Three LED's draw a total current of 90mA. Due to the lower drain (compared with a bulb), and the fact that the LEDs still provide usable light output at 5mA, the LEDlite will run for 40 hours...and even about a day longer at less light output! Before getting into the construction details, let's review a little history of the incandescent bulb to understand why it is such a "power-hog".
Edison mass-produced light bulbs in 1880 with carbonized sewing-thread filaments. See some examples at www.edisonian.com. Check out the antique bulb collector at www.maxmon.com. Improved filaments are used today, such as tungsten, but the original Edison screw-in bulb base persists to this day! Most of the energy is converted to heat and IR, only a few percent comes out as light. That's why the "China light" only runs 4 hours. Semiconductor Light Emitting Diodes use an entirely different means to convert electricity to light, and do not have any of the drawbacks of Edison's light bulb
You can obtain the parts from the vendors directly, or buy a complete kit from Transolve (contact johnf@apk.net for current kit price). This kit includes a pre-drilled case, and the resistors are presoldered to the LED's. If you get the case from Mouser, use a ruler and scribe to mark the LED hole centers. The centerline of the 3 LEDs is 7/32" down from the top of the case. The center LED is 7/16" from the left side of the case. The leftmost and rightmost LEDs are 1/4" away from the LED in the center. Carefully centerpunch the hole centers (don't crack the case), and drill 1/16" pilot holes. Then drill each LED hole with a #11 bit. Use a drill press if available, or your LEDs may be crooked!
The longer lead of the LED is the anode (+). The short lead is the cathode (-); also marked with a flat on the case. Cut the longer lead down to 1/8" in length. Trim one end of each resistor to 1/8". Carefully solder the short end of each resistor to the + lead of a LED. It's easy if you put the LED in a vise. Lay the 1/8" leads of the LED and resistor next to one another (not end to end), and carefully apply solder. Hold steady while it cools. Do not heat for more than 3 sec., or the LED may be damaged. If rework is necessary, let it cool, and try again
Insert the 3 LED/resistor assemblies into the LED holes in the case. Position as shown in the photo. It helps to apply a tiny amount of epoxy (from inside the case) to hold each LED in. Don't get any on the leads! Bend the lead of a resistor (not the center one) at 90 degrees and position to contact the other 2 resistor leads. Solder and trim. Bend one of the LED - leads at 90 degrees to contact the other LED - leads. Solder and trim. KEEP A LOW PROFILE SO THAT THE LID WILL FIT! Trim the black wire from the case so that it will reach the junction of the 3 LED - leads. Strip and tin the end of the black wire, and solder to the LED - "bus". The red wire has to be fed thru the hole at the bottom of the case, near the LEDs. Pull it thru, and trim to about 1" long. Strip and tin the end. Solder the red wire to the resistor "bus".
Ready for testing!
Install 3 AA alkaline cells (or carbon zinc to save money, but with half the life). Turn on the slide switch, and you should see the light! If all 3 don't come on, check all connections. You may have a short, open, or bad solder joint. After checkout, you can apply some RTV silicone rubber behind the LEDs to add strength. Install the back cover and screw
CONCLUSION
Your LEDlite will fit in a shirt pocket, and put out enough light to read a newspaper in the dark, or change a car tire at night. You can proudly display your accomplishment to your friends...but watch out...they will want one
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