8 Ohm Speaker on Arduino: tone() Simulator

At a glance

The Speaker, 8 ohm in brief

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

The 8 ohm speaker in most Arduino kits is a 40 mm paper cone on a voice coil, with two tags and no polarity. Its low resistance is the whole lesson: an Uno pin wired straight across 8 ohms is close to a short, so the pin sags to about a volt while trying to source far past its 40 mA absolute maximum. The Arduino’s own toneMelody example puts 100 ohms in series for that reason, which here gives about 46 mA with the pin holding its voltage; for more volume, drive it through a transistor. Mokxi treats the coil as a real resistance, set by the ohms property, and times each push of the cone from the current through it, rising past 4 mA after falling under 2 mA, to report the note in hertz, however the pin or an H bridge drives it. tone() runs from a timer interrupt as on a real board, and on an Uno it takes timer 2, so PWM on pins 3 and 11 pauses while a note plays. Loudness, coil inductance and the power rating are not modeled.

Family: Outputs
Pins: 2
ohms: 8; the voice coil's resistance, 8.

Pins

2 pins

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

What it does

1

One tag.

2

The other. Either way around.

How to use it

How to use an 8 ohm speaker with an Arduino

Put 100 ohms in series: pin 8 to the resistor, the resistor to one speaker tag, the other tag to GND. That holds the current to about 46 mA with the pin’s voltage held up, where the bare speaker would drag the pin down to a volt. For a louder note, or to keep well inside a pin’s limits, switch the speaker with a transistor from 5 V.

tone(8, 440) starts a square wave from a timer and returns at once, and noTone(8) stops it. The music box here makes each note itself instead, toggling the pin with digitalWrite() and delayMicroseconds() for as long as the note lasts, so you can read exactly what a square wave is. Either way, the speaker shows the note it hears in hertz.

Part pin

Board pin

Tag 1, through 100 ohms

Pin 8

Tag 2

GND

On an Uno, tone() takes timer 2, so PWM on pins 3 and 11 pauses while a note plays. On the XIAO and the Uno R4, put the speaker on a PWM pin.

Arduino Uno: music boxlive0.000 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

A note on the speaker with tone()

#include "pitches.h"
void setup() {}
void loop() {
  tone(8, NOTE_A4, 200);   // an A for 200 ms on pin 8
  delay(400);
}

How it is modeled

What is true about the Speaker, 8 ohm, here

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

Modeled

The coil is a real 8 ohm load. With 100 ohms in series from a 5 V pin it takes about 46 mA and the pin holds its voltage; straight on the pin, the pin sags to a volt or so and would be sourcing far past its 40 mA absolute maximum, which a multimeter in series shows.

The note. The part times each push of the cone, the current through the coil rising past 4 mA one way after being under 2 mA, and reports the frequency in hertz. It counts a pin toggling against ground, against 5 V, or an H bridge driving both ends alike.

Not modeled

Loudness: the probe is a frequency and says nothing about level, which on a real speaker rises with the current and falls off at the bottom and top of its range. The coil's inductance, its power rating (usually half a watt) and burning out.

From Speaker (8 ohm), in full.

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