| This is a good beginner project for
soldering and circuit building. I had a screw that was
recessed about six inches inside a dark hole. I tried
shinning a light into the hole and I could see the screw
head but when I put the screwdriver inside it blocked the
light. I thought about it a while then decided that if I
could put a small light inside the hole, then I would be
able to see the screw head while I tightened it.
The Basic LED circuit is just a led, a
resistor, and a DC power source
The led I used was a white one from Radio Shack. I also
picked up a pack of 100 ohm resistors of the 1/2 watt type.
I looked around the house and found a big six volt square
battery. The value of the resistors used will depend on the
DC source and the type of LED. The LED from Radio Shack has
a voltage of 3.5 and an amperage of 20mA. The LED has two
legs with the longer one being the positive side. The
resistor(s) are soldered in series to the longer leg with
the shorter leg wired to the negative side of the battery.
The only thing we have to do is figure out the value of
resistor to use. The led draws 20mA and since it is in
series with the resistor, then the resistor will also draw
the same amperage. The led has a voltage drop of 3.5 volts.
The source is 6 volts, so the resistor must have a voltage
drop of (6 - 3.5) or 2.5 volts. Using ohms law (E=IR) and
substituting the values.
2.5 = .020 multiplied times
R or R = E divided by I. R = 2.5 divided by .020
R =125 ohms
The value is not critical in this application and a
single 100 ohm resistor will work. I you want to use a
12volt source, then the value of the voltage drop across the
resistor will be 12volts minus 3.5 volts or 8.5 volts.
R = 8.5 divided by .020
R = 425 ohms
I wired the resistor to the LED by just soldering one end
to the longer led of the led and then soldering some red
copper wire to the other end of the resistor. I used a piece
of heat shrinking tubing and covered up the bare metal of
the longer leg of the LED and then over the resistor and
bare metal of the wire. Heating the tubing shrunk it down to
provide insulation for that side of the circuit. I then
attached a black wire to the shorter led of the LED and I
put a bigger piece of heat shrinking tubing over all the
bare metal up to the head of the LED. This made it a stiff
insulated piece that I could drop down into the hole with
just the wiring sticking out going to the battery.
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