Why is this useful? Well if the signal is continually on (HIGH) 25% of the time and off (LOW) 75% of the time repeatedly, and HIGH is a 5V level and LOW is a 0V level, then on average the output will be 25% of the HIGH value. In one sentence, think of pulse-width modulation as a square wave with a variable relative “width” of the HIGH and LOW portions of the wave but keeping the width of the combined wave-shape the same. As described in “ Secrets of Arduino PWM” it can even be generated “by hand” by turning IO pins on and off at the right moment, but the real strength of a microcontroller is having this kind of facility built right into the hardware. The Arduino, or more specifically the ATmega328 on which it is based, has several options for creating pulse-width modulation (PWM) signals. I’ve used my Arduino PWM Output Filter Circuit and connected it to a small portable amplifier and speaker. The audio output will be happening on pin 9, so that pin needs to be connected to your output device (speaker and resistor, or output circuit), then connect the return or GND signal to GND on the Arduino. Optional oscilloscope to observe the outputs.Optional Arduino PWM Output Filter Circuit.1x 220Ω resistor and 8 ohm speaker or old headphone speaker.If you are new to Arduino, see the Getting Started pages. Working with Atmel AVR Microcontroller Basic Pulse Width Modulation (PWM) Peripheral.Sparkfun What is Pulse-width Modulation.These are the key Arduino tutorials for the main concepts used in this project: I am not responsible for any damage to expensive instruments! Warning! I strongly recommend using old or second hand equipment for your experiments. There is a design for an output shield in this post here.In Part 2 there is an alternative version using a different pin for the Arduino.Up to this point I’ve been using a range of audio output options, of varying fidelity, including outputting “PWM” using the Mozzi synthesis library, but I haven’t actually experimented with PWM, or Pulse Width Modulation, itself directly so thought it was time I looked into it a bit more.
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