I am electronic illiterate. If a computer part breaks I debug which part it was and swap it out for a new one. That is the extent of my electronics skills. For years I have been wanting to build a ground light kit for one of my bicycles. Years ago a purchased a bunch of parts, after talking with a clerk at a local Radio Shack. I’m finally settled enough to have dug everything out and it rekindled my desire to build this kit.

These are the parts I have:
2x Mini Toggle (rated 6A at 125VAC, 3A at 250VAC) #275-634

Pkg of 5 9V Battery Snap Connectors #270-324

1 spool Alpha Fry Electrical Repair Solder. Alloy 95% Tin 5% Antimony Solder with Rosin Flux Core. Melting point of 464F. #31955

100 Ft. (30.38m) Hook-up Wire. Rated 300 volts. 22-gauge. Solid. 80C. 1/64″ PVC #278-1215

Pkg of 10 Heat Shrink Tubing #278-1627B

1x Weller Complete Soldering Iron Kit. 25 Watt. 750F. SP23L Iron. MT1 1/8″ Chisel Shaped Tip. Soldering aid. Coil of lead-free solder and metal iron rest.

50 Green LEDs. 15000mcd 5mm. Wavelength 515-525. MCD 12000-15000. VF(V) 2.8-3.2max. Degree 20. From http://www.goodwillsales.com.

Assuming all of these parts will work for my basic needs, what I want to build is a small setup that will allow me to focus Green light onto the ground below my bicycle. I envision 2 LEDs pointing down towards the front wheel, 2 pointing down in the space between the wheels, and 2 pointing down towards the back wheel. I had assumed that I would need 2 9 volt batteries to power them because the package says they are 3.2v max. I saw myself wiring them up 3 to a battery with 1 switch for each of the 2 batteries. Beyond those basic assumptions, I’ve absolutely no idea what I am doing.

I need some advice and direction from our talent hardware experts to guide me on my way. I’m not really sure how to get started. How exactly to wire these up. If what I bought will work for this project. etc.. I am also do not really understand if I need resisters or how to pick the right ones? There are some that came packed in with the LEDs but all of the literature talks about 12 volts, I think they assumed you would use the LEDs in a car.

As far as tools, I have the basics. Wire cutters, an area I can work in. That is about it. Do I need to buy a multimeter for this project to find out any information before I start?

Thanks!

[RunnerPack]

For starters, you’re going to need some resistors to limit the current, or the LEDs will burn themselves out (leave it to a RatShack “expert” to forget that ;-)).

Secondly, with the resistors in there, and the three LEDs being so close to the 9V’s “nominal” voltage, it’s going to have quite a lot of power left when the voltage gets too low to light the LEDs. I would go with multiple parallel strings of two LEDs (and one resistor) each, and put the batteries in either series (18V) or parallel (9V).

You can find calculators online that will help you design LED circuits. Here’s a pretty good one that can do arrays like that I described above. I attached a pretty good one.

Third, since you have 50 LEDs, you might want to use more than six, which wouldn’t be very bright at all. Of course, you have to weigh desired brightness against battery life, so it’s up to you.

• This reply was modified 10 years, 6 months ago by RunnerPack.

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thanks runnerpack. i am still confused as where to start but you have given something more to research. i’m currently reading up on parallel vs. series and now to add in resistors into that.

the LEDs i got seem pretty bight when hooked up to two AA batteries. based on that i thought that 6 would meet my needs, but you are right, more might be better. i’m happy to use as many as i can to create as bright of a light as possible. i do have enough room on the bike to mount 2-4 9 volt batteries without issue.

Lester Knight wrote:
thanks runnerpack. i am still confused as where to start but you have given something more to research. i’m currently reading up on parallel vs. series and now to add in resistors into that.

If you look at the ASCII diagram I posted, the horizontal lines are supposed to be series strings of five LEDs and one resistor. The plus signs at the ends stand for a vertical wire connecting each of these series strings in parallel with one another.

the LEDs i got seem pretty bight when hooked up to two AA batteries. based on that i thought that 6 would meet my needs, but you are right, more might be better. i’m happy to use as many as i can to create as bright of a light as possible. i do have enough room on the bike to mount 2-4 9 volt batteries without issue.

Well, you might want to just make one string as in the diagram (mine, one you generate with the calculator, or any other) and hook it up to check its brightness in the environment it’s most often going to be running in. If it’s too dim, just make another string, put it in parallel with the first, and check it. Lather, rinse, repeat 😉 Also, since you have multiple switches, you could use them to set up “low and high beams” so you can balance brightness and battery life “on-the-fly”.

If you’ve never soldered before, here’s some advice:

1. The iron is not there to melt the solder. The iron’s job is to heat up the metal you’re joining (in this case, mostly LED and resistor leads, and a few wires) and it is this metal which should melt the solder.

2. The solder will attempt to flow toward the heat source, so add solder to the opposite side of a joint from where the iron touches it. The hissing noise is the flux boiling off, and it’s a good thing; no flux = “cold” (bad) joint. Also, contrary to the old saying, a “bigger blob” does not do a “better job” 😉

3. You don’t need to worry too much about polarity on the LEDs, as long as you keep the entire string pointed the same way. LEDs have two ways to show polarity: a flat spot on the plastic part, and one lead is longer than the other. Keep connecting the longer to the shorter (or the flat side to the round side) and add the resistor to either end. If it doesn’t light when you connect the battery, just swap ends (if it still doesn’t light, you have a bad solder joint or bad component).