# Of Resistances and Bending Them

Resistances employed in electronic/ electrical circuits are of the carbon resistor variety and hence small in size, prompting the use of coloured bands to specify the value of the resistor in question. Colour-coding is standardised by the Electronic Industries Association (EIA). Use the Resistor Colour Code Chart (above) to understand how to use the colour code system. When looking at the chart, note the illustration of three round resistors with numerous colour code bands. Depending upon the actual value of the resistor, there will be different number of coloured bands present. Moreover, differing number bands imply different amount of information being provided. For instance, a 10k ‎Ω resistor will have 2 bands for 2 digits of its resistance value, 1 band for the multiplier to that value and 1 band to indicate its tolerance value; in contrast a 276 ‎Ω resistor will have 3 bands for 3 digits of its resistance value, 1 band for the multiplier (which is 1 in this case), 1 band for its tolerance value and 1 band to indicate the temperature coefficient of the resistor.

How to read a typical 4-band, 5-band and 6-band resistor:

4-Band: Reading the resistor from left to right, the first two colour bands represent significant digits , the third band represents the decimal multiplier, and the fourth band represents the tolerance.

5-Band: The first three colour bands represent significant digits, the fourth band represents the decimal multiplier, and the fifth band represents the tolerance.

6-Band: The first three colour bands represent significant digits, the fourth band represents the decimal multiplier, the fifth band represents the tolerance, and the sixth band represents the temperature coefficient.

Definitions of colour bands: The colour of the multiplier band represents multiples of 10, or the placement of the decimal point. For example: ORANGE (3) represents 10 to the third power or 1,000. The tolerance indicates, in a percentage, how much a resistor can vary above or below its value. A gold band stands for +/- 5%, a silver band stands for +/- 10%, and if there is no fourth band it is assumed to be +/- 20%. For example: A 100-Ohm 5% resistor can vary from 95 to 105 Ohms and still be considered within the manufactured tolerance. The temperature coefficient band specifies the maximum change in resistance with change in temperature, measured in parts per million per degree Centigrade (ppm/°C).

Example (from chart): Lets look at the first resistor on the chart. In this case, the first colour band is BROWN. Following the line down the chart you can see that BROWN represents the number 1. This becomes our first significant digit. Next, look at the second band and you will see it is BLACK. Once again, follow the line down to the bar scale; it holds a value of 0, our second significant digit. Next, look at the third band, the multiplier, and you will see it is ORANGE. Once again, follow the line down to the bar scale; it holds a value of 3. This represents 3 multiples of 10 or 1000. With this information, the resistance is determined by taking the first two digits, 1 and 0 (10) and multiplying by 1,000. Example: 10 X 1000 = 10,000 or 10,000 Ohms. Using the chart, the fourth band (GOLD), indicates that this resistor has a tolerance of +/- 5%. Thus, the permissible range is: 10,000 X .05 = +/- 500 Ohms, or 9,500 to 10,500 Ohms.

Once you have understood the colour coding scheme elucidated above, it becomes convenient identifying resistor values. In case there is ambiguity or confusion as to what colour the bands are, it is preferable and easy to utilise a multi-meter to find the value of the required resistance.

In order to understand how to use the resistor bender, check out the video given below:

You never know which resistance you will need when you are making stuff with electronics or just tinkering with some stuff. MakersBox sells a Resistor Box, that has 18 Different Values from 4.7 Ohms to 10 Mega Ohms, and comes with a 3d Printed Resistance Bending Tool, you can buy it from Amazon. Each of these resistances are rated for a 1/4 Watt and have a Tolerance of 5%. The Box also contains a Quick Guide on How to read the Resistances

In case you have a 3D Printer and would like to 3D Print your own Resistance Bending Tool, check out the design by Dan Newman at Thingiverse, Download the STL file and get printing (It takes about 30 minutes for this print) http://www.thingiverse.com/thing:26025

While you wait for your own 3D Print to come out, why not enjoy a timelapse of how we printed this on our printer

Credits:

 Resistor Color Code Chart – ITLL, University of Colorado at Boulder

 Resistance Bending Tool – Dan New Man, Thingiverse