Resistor in a Circuit: Values, Wiring and Live Demo

At a glance

The Resistor in brief

What it is, and every setting the properties panel gives it.

A resistor has no idea which way around it is wired. Each of its two pins is driven from whatever the other pin sees plus the drop its own current sets, which is Ohm’s law applied with no special cases: the same part is a pull-up to the supply, a pull-down to ground, the top half of a voltage divider, and the series limiter in front of an LED. It does not need a shared solve to behave, so on its own it never forces anything else on its net into one; wired next to a capacitor or into a 555’s timing network it joins that solve properly, as a plain conductance. There is no destructive limit modeled: pick a value far too small and the part reports a current a real resistor could not survive, rather than failing, which is a safe way to see the mistake on the probe without losing a part.

Family: Basics
Pins: 2
value: 1000; the resistance in ohms. 220 for an LED, 10 000 for a pull-up, whatever a divider or a timing network calls for.
power: 1/4 W (or 1/8 W, 1/2 W, 1 W, 2 W, 5 W, 10 W); the power rating, from 1/8 W to 10 W. The common through-hole resistor, and the default, is 1/4 W.

Pins

2 pins

Named as the editor names them, so a wire lands where you expect it.

What it does

1

Either end. There is no "in" side.

2

The other end.

How to use it

How to pick and wire a resistor

A resistor sets how much current flows for a given voltage: current = voltage / resistance, Ohm’s law. Its most common job next to an Arduino is limiting an LED’s current. With 5 V on the pin, about 2 V across a red LED and 220 ohms in series, (5 - 2) / 220 is about 14 milliamps, bright and safe for both the LED and the pin.

A resistor has no polarity, so either way around is fine. Its value is in the color bands, or in the properties panel in the editor. The other two jobs you will meet early are pull-ups and pull-downs, which hold an input at a known level, and voltage dividers, which scale a voltage down for an analog pin.

Part pin

Board pin

Either leg

Pin 13

The other leg

The LED’s anode; the LED’s cathode to GND

The resistor goes in series with the LED on any board. For 3.3 V logic the same arithmetic, (3.3 - 2) / 100, gives 13 milliamps from a 100 ohm resistor.

Arduino Uno: first blinklive0.000 s 0.00x

Click to open it in the editor

This is the simulator itself, running here. Click anything to open it in the editor.

Open this project in the editor Read the full tutorial

How it is modeled

What is true about the Resistor, here

In its help article’s own words: what the simulation gets right, and where it stops.

Modeled

A resistor does not need a matrix to behave, so on its own it never creates an analog island. But when one reaches it (the series resistor of an RC network, the two timing resistors of a 555), it joins the island and is stamped as a conductance instead of passing a Thevenin equivalent along, and its current probe still reads the same current either way.

Not modeled

No tolerance and no temperature coefficient: its value does not drift as it warms. No Johnson noise, no parasitic inductance or capacitance, and no preferred-value grid: any positive number is a resistor, where a real bin holds E12 or E24 values only.

From Resistor, in full.

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