Definition: What is a Resistor?
A resistor is an electrical component with two terminals that is used to limit or regulate the flow of electrical current in electronic circuits. Its purpose can be varied, as resistors are used to reduce current flow or lower/raise voltage levels in a portion of the circuit. A resistor is also meant to regulate the actual load on the system, meaning that it consumes some amount of electricity and dissipates it as heat, thereby reducing the amount of electricity (current) flowing out of it by specific amounts related to the resistance value.
Explaining a Resistor
The resistor is one of the most important components in an electronic circuit as it allows the designer to precisely control the amount of current and voltage flowing at certain areas in the circuit. Therefore, it is an absolute requirement to ensure that sensitive electronic components such as integrated circuits (ICs) receive the precise amount of power that they require and nothing more, as an incorrect load often leads to degradation or outright burnout of ICs.
A resistor, though very small, is often made up of copper wires coiled around a ceramic rod and an outer coating of insulating paint. This is called a wire-wound resistor, and the number of turns and the size of the wire determine the precise amount of resistance. Smaller resistors, those that are designed for low-power circuits, are often made out of carbon film, which replaces the wound copper wire, which can be bulky.
Pull-Down/Pull-Up Resistor
A pull-down resistor's primary function is to serve as a drain for excess charge or current within a circuit. The excess charge or current is drained to the ground (GND) voltage of the circuit. For example, if a circuit's voltage is measured while a push-button circuit is closed and that push-button is connected to a voltage supply of 5-Volts, the voltage will read 5-Volts at the input. When the push-button circuit is opened, the 5-Volt supply is no longer connected to the input, and the excess charge in the area of the circuit being read will be drained through the resistor until the voltage at the input reads 0-Volts.
A pull-up resistor works in the same manner, but instead of being referenced to the ground (GND) voltage, it pulls the signal value "Up" to the supply voltage (Vcc) and the push-button example above would connect the input to the ground (GND) voltage.
Current Limiting Resistor
A current limiting resistor's primary function is to limit the current drawn by a component within a circuit or from a voltage output. Some components, like LEDs, must have their current draw limited or they will consume more power than intended and damage themselves. Other devices, such as microcontrollers, have a maximum current that their output pins can supply. For these devices, current limiting resistors restrict the amount of current any device on that circuit can draw from the output pin, thereby protecting the microcontroller from becoming damaged.
Resistor Values
The outside of the resistors found in Tech-Box.io kits are marked by four bands of different colors equidistant to each other and a fifth band slightly farther from the fourth compared to previous spacing. The combination of the colors represents the value of the resistor in ohms. The bands are read from left to right, with the first three color bands representing the base value as individual digits, while the fourth is a power multiplier and the last is a tolerance indicator (because manufacturing processes limit the preciseness of the value). If there are four bands, as on some resistors not supplied in Tech-Box.io kits, the first two represent the base value, whereas the last two still represent the multiplier and tolerance, respectively. The color-value key for determining resistor value is listed below.
Color value representation:
- 0 = Black
- 1 = Brown
- 2 = Red
- 3 = Orange
- 4 = Yellow
- 5 = Green
- 6 = Blue
- 7 = Violet
- 8 = Grey
- 9 = White
Tolerance:
- Brown = +/- 1%
- Red = +/- 2%
- Gold = +/- 5%
- Silver = +/- 10%