Resistors are the most common component in electronics. The better you understand them, the easier learning everything else in electronics will be.
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Basic electrical properties
- Limits current to series components, from power supply, etc.
- Divides voltage.
- Pulls up/pulls down voltage.
- Generates heat (power). Must be able to safely dissipate that heat (wattage rating).
Resistors have resistance. That means that they limit current based on the voltage across them.
- Ohms: (Ω symbol) – The unit used to indicate the amount of resistance.
Resistors also get hot due to current being forced through them.
- Wattage rating/Power (P): The ability of a resistor (or other component) to dissipate heat. Most resistors are 1/4W (one quarter watt). Wattage should actually be kept 1/2 of the rated value, so 1/8W (0.125W) or less for a 1/4W (0.25W) rated resistor. Multiply the voltage across the resistor by the current flowing through it to find the watts …. P = V/I
The primary role of the resistor component is to limit current. Here is one way to build a circuit on a breadboard where a resistor limits current going through an LED.
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More detailed resistor information
Terminology and other general properties.
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- Through hole resistors, which hobbyists mostly use, are usually blue (sometimes beige), with 5 stripes/bands (4 for beige) that indicate it’s rated value and tolerance.
- Ohms: The unit of resistance. Higher value resistors result in less current for a given voltage.
- Tolerance: Percentage higher or lower than the rated value that can be expected. Typically 1% for blue resistors and 5% for beige resistors.
- Ω (Greek letter Omega) is the symbol used to indicated resistance in ohms. 1KΩ is one thousand ohms (one kilohms). Also commonly just referred to as a 1K resistor.
- Schematic symbol is almost always a jagged line when drawn by someone in the US, while it is often drawn as a rectangle elsewhere. The recommended value is usually written next to it (in the rectangle). It’s usually safe to assume that a 1/4W resistor will be work unless a different wattage is noted.
- From time to time, you will see a resistor value written like 1K5. That indicates that it is a 1,500Ω (1.5K) resistor. The K for Kilo is sometimes used to replace the decimal point because it is easy to not see the decimal point.
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Main resistor topics
- Current limiting (Ohms law) Resistor limiting current – Ohms law . Very important!
- Voltage division Voltage divider – Setting a fractional voltage
- Power/Wattage (heat) generation and dissipation.
- Series Series resistors
- Parallel Parallel resistors
- Color code
- Pull up/down
Other basic components
- LEDs (light emitting diodes) Light Emitting Diodes – Indicator LEDs
- Switch (push button) Momentary tactile push button switch on prototype breadboard
- Capacitors Capacitor component
- Rectifier diodes
- Trimmer potentiometer (trimpot) Trimpot – Trimmer potentiometer – Voltage divider – Variable resistor
- Light Dependent Resistor (LDR)/Photoresistor Light Dependent Resistor LDR component – Photoresistor
- NPN Bipolar Junction Transistor (BJT) NPN Bipolar Junction Transistors (BJTs)
- PNP Bipolar Junction Transistor (BJT) PNP BJT switch – Bipolar Junction Transistor – 2N3906
- Zener diodes
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