Soldering

Tools that will be used for this project are a soldering iron (with solder) to combine electrical components, wire strippers, and optional use of a helping hands utility or vise as a stabilizing tool for materials being soldered.

Components being used are 1 red, yellow, or green LED, 1 300 Ω resistor, about 6 inches of insulated wire, 2 AA batteries, a dual-AA battery holder, and 1 push button.*

If you do not have access to a dual-AA battery holder, some tape can hold together the AA batteries in a pinch, although this is not recommended.

*A full schematic of the following instructions is included at the bottom of this page.

*WARNING*

Soldering irons melt solder by becoming VERY hot (400 °F)! Hold the soldering iron like the picture to the left, only on the insulated handle. NEVER touch the metal heating rod before, during, or after plugging in and turning on the soldering iron.

Do not place the soldering iron on anything flammable or meltable. Most soldering irons come with a small metal stand; place the hot iron directly on the metal stand when not in use.

Always solder in a well ventilated area with lots of space to ensure no mishaps occur. Do not directly inhale burning solder fumes.

If you have not yet used your soldering iron, you will need to tin, or prepare, it. To do this, heat up your soldering iron (10-15 minutes depending on the brand), touch a piece of solder to the iron head, and clean off excess solder using steel wool.

If you have already tinned your soldering iron, continue to the next step: Solder the Button.

A push button has four legs, each in a pair on one side of the button. Circuits flow across these pairs, meaning for the button to have effect, the components attached to it must be on the same side of the button. Using your wire strippers, cut your wire into two equal pieces (each about 3 inches) and strip a half inch of insulation off of each end to expose the metal wire inside. Affix your wire to one side of your helping hands and the button to the other side. Move the helping hands contraption until the the wire touches one leg of the button. Heat up solder on your soldering iron until a small sphere of solder is on the end of your soldering iron. Touch the soldering iron, with additional solder near by, to the wire and button's leg until the two have become covered. Remove the soldering iron. The solder should harden within seconds. Give a light tug to your two components to ensure the pieces are securely attached to one another.

A resistor is a nonpolar electrical component that resists the flow of a circuit and limits current. Being nonpolar, it does not matter which leg of the component is soldered to which side of the circuit. Using the soldering steps previously stated, solder the resistor to the button leg that is on the same side as the wire.

An LED, or Light Emitting Diode, is a polar component. Therefore, the leg that you solder to your circuit is VERY important or it will not light up. One leg of the LED is longer than the other, this is denoted as the "postitive" leg, while the shorter leg is the "negative" leg. If the legs are the same lengths (which would only be the case if the LED had been cut), the positive side will be flat at the base of the LED. Solder the positive LED leg to the remaining leg of the resistor.

At this point, we have created a polar circuit. The side with the wire currently attached (leading in to the positive LED leg) is the positive wire. This is where our battery's positive terminal will attach to our circuit (positive to positive). Strip (about half an inch on each side) and solder the remaining 3 inches of wire to the negative leg (short leg) of the LED. This wire will be denoted as the negative wire. If you think you may get confused, grab a sharpie (of a different color than your wire) and make a line on the positive wire. Additionally, the button goes before the LED in the circuit, and therefore the wire touching the button is the positive wire.

Most circuits with a battery will use a battery connector which holds the battery and allows its terminals to be accessed through a positive and negative wire. If you have one of these components, skip to the next step. Otherwise, you will have to create a makeshift battery holder. Take a piece of electrical tape and affix the two batteries together to create one long battery. Make sure that one negative side connects to one positive side in the battery (the flat side (-) to the raised side (+)). You now have a single (double) battery for your circuit! Use more tape to affix the positive wire to the raised side of your battery (+), and the negative wire to the flat side of your battery (-).

If you created your own battery holder, skip this step. Otherwise, place two AA batteries into the connector. Solder the red wire (positive) to the positive wire of the circuit and the black wire (negative) to the negative wire of the circuit.

Give the button a press and the LED should light up! If it does not light up, check your soldering joints, the direction of your LED, the direction of the battery connector, and the battery within the connector.

Within the instructions, it was told that a red, yellow, or green LED must be used with this circuit. This is because each LED color actually has different voltage requirements due to the color they emit. A combination of two AA batteries (1.5V each), is a total of 3V. A red LED has a forward voltage of 2.0V, yellow 2.1V, and green 2.2V. Blue has a forward voltage of 3.5V and white has a forward voltage of 3.2V, both of which are too high for our power supply. Of course, these LEDs could still be used within this circuit, they would just produce a much dimmer light than the former colors.

As per the resistor, you must use Ohm's law to find the resistance necessary. In my case, I had two resistors that I could use: a 300Ω resistor or a 10KΩ resistor. Ohm's Law states that Voltage (V in volts) / Resistance (R in Ohms Ω) = Current (I in amps (A)). We know that we have 3 Volts, and most LEDs require a current between 10 and 30 milliamps (mA). Let's try each of our resistors with the equation:

• 3V / 300Ω = 0.01A or 10 mA
• 3V / 10,000Ω = 0.0003A or .3 mA

Therefore, to attain our 10-30 mA, we must use our 300Ω resistor.