In this course we will see what is a resistor, how to calculate its value and to know which resistor is adapted to your project.
Then we will see a software from our application “Arduino factory” to calculate the value of a resistor.
It’s composed of a ceramic rod to limit the current. The both pins connect the resistor to the circuit thanks to nickel capsules. Finally, there is a spray to protect the resistor and display the rings of color.
Therefore there is a bette stability of the temperature and a tolerance from 0.5% to 2%.
We can now take the example of a circuit of a led and an arduino board. This is the characteristic of the red LED:
Vled = 1,6 V and Iled = 8 mA
This is the mesh equation:
The value of the resistor is calculated according of the color of its rings: 2 rings for the value, one ring for the multiplier and one ring for the tolerance.
We will see now how to calculate the value of a resistor with its rings.
First of all, you have to know that each resistor has a different number of color’s ring:
Furthermore each ring as a different meaning :
Here is some examples:
Example
1st ring: blue -> 6
2nd ring : yellow -> 4
3rd ring: orange -> 103 Ω
4th ring : red -> ± 2 %
Conclusion
The value of the resistor is: 64 x 103 = 64 000 Ohm = 64 kiloOhm
The tolerance is ± 2 %
Example
1st ring: blue -> 6
2nd ring : yellow -> 4
3rd ring: red -> 2
4th ring: orange ->103 Ω
5th ring: green -> ± 0,5 %
Conclusion
The value of the resistor is: 642 x 103 = 642 000 Ohm = 642 kiloOhm
The tolerance is ± 0,5 %
Example
1st ring: blue -> 6
2nd ring: yellow -> 4
3rd ring: red -> 2
4th ring: orange ->103 Ω
5th ring: green -> ± 0,5 %
6th ring: violet -> 5 ppm/C°
Conclusion
The value of the resistor is: 642 x 103 = 642 000 Ohm = 642 kOhm
The tolerance is ± 0,5 %
The temperature coefficient is 5 ppm/C°
A resistor has at minimum 4 rings but sometimes the last ring is missing. It doesn’t affect the accuracy of the value of the resistor because it miss only the tolerance. Therefore we will take the largest tolerance, which is 20%.
The multiplier:The multiplier ring is used to know at which power of 10 you need to multiply the significant digits. In fact, there are 220 ohms resistors or even 10 000 ohms. Thanks to the multiplier ring you know which power of 10 is situated the resistor.
The tolerance: When the resistor is made, the manufacturer give it a value. Nevertheless the value can change a little bit even if there is the same rings. That’s why there is a tolerance to notify the user that the value of the resistor may vary a little bit.
Do you think that calculate the value of a resistor is difficult and fastidious? We have created an android application which will do it by itself!
This application can be useful in all your project. You can find in it a resistor calculator, some course about the components and a remote control to control all your projects with bluetooth!
Don’t hesitate to download Arduino factory Application: https://play.google.com/store?hl=fr&