The Tech Blog

Last week, we dove into the fundamentals of resistance, exploring what it means and how it works. Continuing on that, folks starting out on electronics need to know how to read through resistors by appearance.

For through-hole resistors, a color code band system was introduced a century ago by the Radio Manufacturers Association (RMA) in the U.S. It became widely standardized as part of military requirements during World War 2. The first two (or three, in precision resistors) bands denote significant digits, the next one is a multiplier, and the final band represents tolerance. For example, a resistor with bands of brown, black, and red corresponds to 1, 0, and a multiplier of 100, making it a 1,000-ohm resistor (or 1 kΩ)

To make this easier to memorize, we use the classic mnemonic like: BB ROY of Great Britain had a Very Good Wife, which stands for Black, Brown, Red, Orange, Yellow, Green, Blue, Violet, Gray, White, representing the digits 0 through 9. The tolerance band is typically gold (±5%), silver (±10%), or none (±20%). Precision resistors can include additional bands for tighter tolerances.

SMD resistors use alphanumeric codes instead of color bands due to their compact size. There are different types here. In the Three-Digit Code type, the first two digits represent the significant figures, and the third digit is the multiplier. E.g, a resistor marked 472 means 47 × 10² = 4,700Ω. For a four-digit code, you get more range in resistors with the first three digits representing the significant figures, and the fourth digit being the multiplier. Eg. 1634 means 163 × 10⁴ Ω. Another type is EIA Codes(E6, E12, E24, E48, E96, E192) Which indicate value by 2 digits and letter as tolerance(Check images). The most common one is the E96 Code which defines 96 distinct resistance values within each decade(10-100 Ω, 100- 1 kΩ etc). 96 values in a decade are derived via a formula such that any resistor in the series is within ±1% of its nominal value.

Understanding these details isn’t just academic, it can be a lifesaver in the field, especially during troubleshooting. Take the time to learn them!

Ok, I wanted to create this for a long time but never got around to sitting down to compile my thoughts on it. I know this is as basic as it gets, but I still wanted to put out a series of posts on everything I know about resistors. Hey, for most in my circle, this might not be the most exciting series, but believe me, while researching this topic, I stumbled upon a few things I didn’t know even after 18 years in this field!

Let’s start then. At its core, resistance is the property of a material that opposes the flow of electric current. But what does that mean from first principles? Imagine a river flowing downstream. If there’s no obstruction, the water flows smoothly. Now add rocks, debris, and narrow passages, the flow slows down. In an electrical circuit, electrons are the water, the material of the conductor is the riverbed, and resistance is the obstruction caused by the material’s atomic structure.

Electric current flows because electrons are pushed through a conductor under the influence of an electric field. However, as these electrons move, they collide with atoms and other particles within the material. These collisions are what create resistance, converting some electrical energy into heat. More frequent the collisions, the higher the resistance.

This phenomenon is beautifully captured by Ohm’s Law, which states that V=IR, where V is the voltage difference, I is the current, and R is the resistance. It tells us how much current will flow for a given voltage across a resistor(Applicable only if the temperature is constant). Now Resistors are just physical devices specifically designed to exhibit and control this property. They are put in circuits to intentionally control current flow and divide voltages.

So, as simple as the concept of resistance may seem, it’s at the heart of almost everything in electronics. Everything on the planet has resistance. Hopefully, in the coming posts, I will like to explore resistors from every angle that I know of.

BTW: Did you know that the smallest resistor ever made is less than a nanometer in size and made of a single molecule?