0.1 Discrete components  (Page 3/6)

E = I x R

Power = E x I = E^2/R = (I^2) x R

You can avoid the second error by applying a good engineering practice: always double the calculated (or measured) power by 2 to get the wattage for the resistor. Simply stated, a ¼ watt resistor should never see more than ⅛ of a watt of power through it.

Picking a resistor

Resistors are usually commonly stocked in the lab. In many cases, they are typical ¼ watt, 5 percent carbon film resistors. This is where the color-code chart becomes handy: to make sure you actually have the resistors you need. Your lab may also have surface-mounted resistors. These are great to use when you need a smaller footprint for the resistor and you have the tools to properly attach them to the printed circuit board.

Color-code chart

Figure 3 Shows a typical resistor color-code chart.

There are many others available if this one doesn’t suit you. You can find more charts here: https://www.google.com/search?q=resistor+color+code+chart&hl=en&tbo=u&tbm=isch&source=univ&sa=X&ei=2XvwUJ_RDcjm2AW084GwDA&ved=0CC4QsAQ&biw=1680&bih=890 .

Digi-Key part numbers

Obtaining resistors for your project should be relatively easy. They are usually stocked in the lab. But if they are not, there is a quick way to order them from Digi-Key while you are ordering other parts.

The part number you will need for any ¼ watt resistor from Digi-Key is put in an easy format. The 1-ohm through 9.1-ohm resistors have part numbers with the form of 1.0QBK-ND through 9.1QBK-ND. The 10-ohm through 91-ohm resistors have part numbers with the form 10QBK-ND through 91QBK-ND. Table 2 lists the general forms for each decade:

Capacitors

There are many capacitors to choose from; that makes it easy to get thoroughly confused when trying to select them. To keep our discussion relatively straightforward, I will describe only a few of the more popular versions.

First, capacitors come in many shapes and sizes, such as:

• Ceramic.
• Electrolytic.
• Tantalum.

They are also used in many different applications, such as:

• Power supplies.
• Bypass capacitors.
• Simple oscillators.

For the purposes of your senior project, these parameters should be adequate. I will assume that you know the theory necessary to be able to use them in a circuit.

This discussion will focus on the real-world use of capacitors in a circuit, or at least the ones you will most likely face while designing your senior project.

Shapes

It is generally easy to determine the type of capacitor by its shape. The two most common shapes are a cylindrical device with two leads, either on each end or both out the same end. In most cases, there will be markings to let you know which side is the positive side and which is the negative side. It is important that you make the positive and negative connections properly or the capacitor could blow up.