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Let There Be Light... and LED Gadgets
by Eric Wonhof


Face it, God got right down to business on that first day. It’s pretty cool stuff… waves… particles… whatever. Who doesn’t need a little glimmer when hiking out after the evening rise, breaking down the setup at the car, or I’ve heard even the very early morning.

There are a ton of specialty lamps on the market for sportsman from headlamps to tying lights. Many of them use LEDs (light emitting diodes) or can be made from them. You can easily make most of these yourself with a couple bucks for the electronics, some household/shop/office items, and a soldering iron. The homemade versions may not be as slick as the store bought types, but they’ll definitely light your way and blind your fishing buddy as well.

Cannibal Gadgets LED’s are small lamps that use little power, don’t burn out (without a lot of encouragement), don’t generate heat like other bulbs, aren’t delicate and in general, they’re cheap (like most components). One of the wonders of the electronic age, they’re used everywhere now; toys, vehicles, appliances, and a lot of other more serious gadgets. The light comes from electro-luminescence, zapping odd bits of material or gas that in turn give off the energy in the form of light. Initially dim and in limited colors, the last 15 years have brightened and broadened their range to the point where they’re replacing the old Edison filament bulbs in almost every small application. Reeling in my egghead fascinations, I’ll go over the basics for a simple LED gadget. Battery, switch, LED, a bit of wire, a resistor all wired in a loop, and that’s it!

There’s are a lot of great info on basic electronics and LED’s. A little research on LED’s in ‘serial’ (one after the next) or ‘parallel’ will allow multiple bulbs to be used.


The Components

The LED

This will be the toughest part to pick out. We’re looking for the high intensity types with a few particular specs. Yes, you have to look at the fine print.
Color: White (red for night vision?)
Intensity: Basically brightness, get the highest you can find for an illuminating device.
Measured in MCDs (thousandths of a candela), you need many thousand of them to really light your way. Through my technical experimentation, I’ve come up with these MCD results: a few hundred = it’s on, a couple thousand = somewhat bright, several thousand = I see spots, over 10,000 = ouch, this is what we want. This may be as high as you’ll find easily, but brighter LED’s are coming on the market daily. The total light generated is a combination of intensity and the angle it’s spread across. A bright narrow LED may not yield as much light as a dimmer but wider LED.
Viewing Angle: 15 to 60 degrees depending how broad you want your light spread.
Size: dependent on the above choices, 5mm and 10mm diameters are both easy to work with.
Forward Voltage (V): dependent on LED chosen, usually 3-4V. This value will strongly influence battery choice. Typical forward voltage is what’s needed to make it run per spec; max forward voltage is the limit you can supply without blowing it up (or cutting it’s life way down). If electricity were a river, voltage would be its speed.
Continuous Forward Current (mA): dependent on LED chosen, usually 20-40mA. If electricity were a river, current would be its size.

The Power Supply (Battery)

Whether watch batteries or small electronics batteries, voltage (V) is what’s most important here. The total voltage of the battery/batteries needs to exceed the LED’s Forward Voltage. Be generous, you can cut this back later with a resistor. You can add batteries together by putting them together in series (head to tail, one leading to the next); two 1.5V batteries add up to a 3V power supply, etc. Don’t send more voltage through the LED than its listed max forward voltage or it blows in a disappointingly small pop. If your battery is just a little lower than the LED forward voltage it will still work, but will be dimmer and drop from there. A battery holder/connector is really nice especially for the small batteries. Batteries are the most expensive component, but they’ll have a long life in these devices.

The Resistor

These are small blocks or filters that cut down the juice. The colored bands on them indicate their rating (decoders for the color code). Also online,“LED calculators” will supply the proper resistor ratings and some even generate basic drawings of your circuit. Just put the appropriate resistor inline after the power supply, and everything is ready for the LED. Don’t try testing an LED with voltage higher than its rated max, or you’ll have to run back to the store or worse wait for another to arrive by mail. Get a small combo pack of ¼ watt (and maybe ½ watt) resistors up to about 300 ohms. If you don’t have the exact ohm resistor, you can go a little lower and run the system hotter and brighter (might cut down LED life) or use a bigger resistor and be safe. There are also ways to combine resistors in parallel. You can always use a higher watt rating than specified (1/4 watt can always be substituted for an 1/8th watt).

The Switch

Not even a necessary part, you can leave bare wires and complete the connection by twisting the ends together. A ‘micro’ slider, toggle or push-button on/off switch will do fine. I pick the smallest available.

Other Tools and Bits

Soldering iron, snips, and maybe strippers. Nearly any wire will work as there is very little power drawn by the LED. Small single or paired conductor wire will do fine. Electrical tape, heat shrink tube or especially liquid electrical tape (like tool dip) is very nice for coating the small components. A hot glue gun (or epoxy), spring clips, and other stray bits from your tool drawer. Scavenge interesting pieces from other broken (or soon to be broken) gadgets.


Basic Circuits

Circuit Arrangement (Putting it all together)

Batteries are direct current (DC), so the electricity flows in a loop out through the components and back. Each component has 2 legs/ends/posts/leads. Connect them one into the next then return to first component. Following the circuit diagram, start at the positive battery post, to the resistor, to the switch, to the LED and back to the negative post of the battery.

This can be done in almost any order with one important exception. LED’s are one way; they only light up when power is put through them in a particular direction. The longer leg of the LED connects toward the positive post of the battery. It won’t blow if power is put through incorrectly unless your battery voltage is too high in which case it would have blown anyway but it will give you something to think about as you’re driving back to the store. Before soldering, I like to set up my circuit held together with clips to test everything. If it all works, solder it up, and you're set!

Here’s the Basic 1 LED Circuit

Basic Circuit

‘Bug Eyes’ 2 LED Pod Project

This is my favorite, and it fits in a small pocket where the eyes (on a bendable wire) stick out. I stuck some velco patches around the back of my truck for attachment points. Works as a flashlight as well. Cost about $6 (half of that was the batteries)

Bug Eyes LED Pod

9V LED Pod Project

Just made this. It’s very small, just the connector, a switch and 2 LED’s all held together in a lump of plastic from a hot glue gun. An elastic headband for a headlamp or strong pinch clip would also complete it well. Cost about $7 (over half was the battery).

9V LED Pod
 

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