Sunday, November 11, 2012

Resistor Color Codes

Most people dealing with electronics these days know how to read a Resistor Color Code Value Chart, but beginners probably dont. This tutorial should walk you through how to read a chart to determine resistors in your projects. So lets get started.

A resistor is a passive two-terminal electrical component that implements electrical resistance as a circuit element [1]. They come in many compositions, but there are three primary ones that people use: carbon film, metal film and wire-wound resistors. For more information about all other kids of resistors, as well as a detailed explanation of the three types mentioned here, refer to the Wikipedia page on resistors.

Classification of resistors consists of three main properties. Resistance, which is measured in ohms, is the actual value of the resistor. Without this, you cant tell one resistor from another. The second is the tolerance value, which is shown as a percentage, and is represented by a color band of its own. The last property is the power rating of the resistor, which is measured in Watts [2].

The value of the resistor, as well as the tolerance percentage can both be found by using the following chart.

Image Source:
For four banded resistors, the first band is the first number in the value of the resistor. The second is the second number in the value. The third is the number of zeroes behind the first two numbers, also referred as the multiplier. For example, Red-Red-Black, would be 220 Ohms. Similarly, 1K Ohms would be Brown-Black-Red.

For five banded resistors, the third band represents a third value, the fourth band is the multiplier, and the fifth band is the tolerance. These types of resistors are usually blue, green or brown, depending on the manufacturer.

The tolerance value represents what error the value known might be off from the actual value of the resistor. Most electronics use the standard 5% or 10% resistors, which is represented by a gold or silver band. Sensors and precision electronics require higher tolerances. Those come as actual color bands. Most precision resistors come with a 1% tolerance (Brown), though, other tighter tolerances can be found. So a 237 Ohm resistor with a 0.5% tolerance would take the 5-banded color code, Red-Orange-Violet-Black-Green.

The wattage rating of a resistor is determined separately by the size of the resistor. The larger the diameter and length of a resistor, the higher wattage it can handle.

Monday, November 5, 2012

ESD-Protective Bags & Packing Foam

So today I wanted to give folks a rundown of ESD-protective materials that are available for those who need to package, store or ship electronics, but just dont know what to get. As a hobbyist electronics person, I know how challenging and sometimes frustrating this can be. You can usually get away with using the little bits of ESD foam that come with your electronics, or even the ESD-protective bags they come in. Sometimes, this isnt enough, or the bags might be damaged, thereby defeating the purpose of using them.

When you are working on a project, small or big, you need to organize your project in bins so that you can constantly keep track of where everything is, and avoid an accidental static discharge that will destroy your precious electronics. I know people usually get lazy about this, and they tend to strew everything across their desk or the floor, as do I as well, but to progress from amateur to professional electronics project development, you have to improve your storage methods to better manage and care for your electronics. So explanation aside, lets get to the good stuff.

First, everyone knows about ESD-protective bags, they come in all sorts of colors and shapes. Some have zip locks and others dont. You've seen the silver ones, the pink ones and the blue ones. Maybe you've even seen the black ones. I'll explain what each is, and the application for it.

The pink/blue/green ESD-protective bags are Anti-Static bags made of low-charging material, meaning they will not create harmful static electricity charges when the bag surfaces rub together, but will not protect the item from electric fields. Depending on your application, you may or may not be able to store sensitive electronics in these. They come in both zip and non-zip styles. These tend to be the cheapest.

 A few things to note about Anti-static bags [1]:
  • Antistatic bags offer NO effective protection against a contact ESD!
  • They should only be used for NON STATIC SENSITIVE components, e.g. nuts, bolts, paper etc.
  • ORDINARY PLASTIC BAGS can generate and hold static charges in excess of 10,000v!
  • Antistatic bags deteriorate with time and wear, MONITORING them is VERY IMPORTANT.

The silver ESD-protective bags are Metalized Shielding bags made with anti-static plastic and a metalized film, which forms a Faraday cage around the item to be protected preventing any localized charges from being deposited onto the protected devices as the bags are handled. This allows them to shield sensitive electronics from outside radiation or radio waves.   A lot of electronics, especially IC chips will come packaged in this type of bag. They come in both zip and non-zip styles. These tend to be more costly than regular anti-static bags, but are used most often. 

A few things to note about Metalized shielding bags [1]:
  • DO NOT CREASE the bag, as this can breakdown the integrity of the metalized shield!
  • Metalized Shielding bags CAN DETERIORATE with use, MONITORING them for effectiveness is VERY IMPORTANT!

The black ESD-protective bags are Conductive polyethylene bags which are both anti-static and shielding. Unfortunately, since they are also conductive, if you build up a static charge by walking across a carpeted floor with shoes, and you hold this bag, everything inside will get damaged. So this bag is for use primarily when it will be grounded at all times, such as in storage. These are most expensive, but have drawbacks for general use, so arent used as often.

 A few things to note about Metalized shielding bags [1]:
  • It is POSSIBLE TO DAMAGE a static sensitive component inside a Black Conductive bag with a contact ESD!
  • Black Conductive bags, holding static sensitive components, should only be handled in an EPA and while the person is grounded in order to ensure that no potential difference occurs.
  • Black Conductive bags allow for a good path to Earth when used with other.

So now you know about ESD-protective bags. For more information on ESD-protective bags, visit Next, I will give a brief rundown on ESD-protective packing foam. Similar to ESD-protective bags, foam also comes in Anti-Static and conductive.

There are many types of ESD-protective packing foam, but the two most used are polyethylene and polyurethane. Polyethylene foam is "closed cell" foam, it has a smooth skin and it tends to be very hard. Besides hardness, it is less likely to retain moisture and more chemically inert than polyurethane [2]. This tends to be the black conductive foam [3].

Polyurethane is "open cell", and you can see the miniature bubbles in cross section.This is a soft foam, and it is good for cushioning [2]. This one tends to be the pink anti-static foam, however, you might find some polyethylene anti-static foam in packaging to secure devices from moving during transport [3].

So there you have it. A brief, quick rundown on ESD-protective bags and foam. For even more information about ESD-protective bags, visit The ESD Journal

I hope this helps your future ventures to storing and organizing your electronics projects.