Resistor Reference
Fixed-value through-hole resistor. Used to limit current into LEDs and other components, or to pull signal lines HIGH/LOW.
Pin names
| Name | Description |
|---|---|
| 1 | First terminal |
| 2 | Second terminal |
Resistors are non-polarised — either terminal can be connected to either end of the circuit.
Attributes
| Name | Description | Default |
|---|---|---|
| value | Resistance in ohms. Accepts plain numbers ("220") or SI suffixes ("1k", "4.7k", "1M") | "1000" |
Common resistance values
| Value | Typical use |
|---|---|
"220" | Current-limiting for a standard LED at 5 V |
"330" | Current-limiting for a standard LED at 5 V (slightly dimmer) |
"1k" | Pull-up / pull-down, base resistor for BJT |
"4.7k" | I²C pull-up |
"10k" | Pull-up / pull-down on digital inputs |
Usage
The most common use is limiting current through an LED. Without a resistor, too much current flows and the LED burns out in real hardware.
Formula: R = (Vsupply − Vf) / If
For a standard red LED at 5 V:
- Vf ≈ 2.0 V, If = 15 mA → R = (5 − 2) / 0.015 ≈ 200 Ω → use 220 Ω (next standard value)
// Pin 13 → 220 Ω resistor → LED anode → LED cathode → GND
const int LED_PIN = 13;
void setup() {
pinMode(LED_PIN, OUTPUT);
}
void loop() {
digitalWrite(LED_PIN, HIGH);
delay(500);
digitalWrite(LED_PIN, LOW);
delay(500);
}Examples
| Description | Attrs |
|---|---|
| 220 Ω (LED current limiting) | { "value": "220" } |
| 1 kΩ | { "value": "1k" } |
| 4.7 kΩ (I²C pull-up) | { "value": "4.7k" } |
| 10 kΩ (pull-up/pull-down) | { "value": "10k" } |
See also
- LED — always use a resistor in series with an LED
- Pushbutton — pull-down resistor keeps the input stable when the button is open