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This may sound like a very dumb question and I apologise in advance.

I've gone through reading about PWM and working on some example sketches to control PC fan speeds using PWM and Arduino.

In all documents I read, it is mentioned that "PWM is a signal".

My questions:

  1. Is PWM really a signal? To me, it looks like an electric current turned on and kept on for a certain time, then off for a while repeatedly. What makes this a "signal"?

  2. If PWM is a signal, why do we need to connect the Ground from Arduino to the ground of the device to which "PWM signal" is being sent to?

This is confusing me because in my mind, for example, radio signals do not need a ground connection. The signal comes and gets read.

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  • The ground wire going from my h bridge to arduino worked itself free recently (bottom left wire connection in the image) while my project was running. The arduino was sending PWM output to the h bridge at the time. The board overheated and died a permanent death in about 2 minutes. I assume this lack of grounding caused the board to overheat?!h bridge wiring
    – robster278
    May 6, 2019 at 20:40

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Is PWM really a signal? To me, it looks like an electric current turned on and kept on for a certain time, then off for a while repeatedly. What makes this a "signal"?

At the most basic, it is a signal because we call it such. Even a constant voltage can be a signal, signalling that e.g. a window has not been broken. A PWM signal indicates that we want to apply a certain fraction of full power to a load.

If PWM is a signal, why do we need to connect the Ground from Arduino to the ground of the device to which "PWM signal" is being sent to?

Because it is a voltage-based signal, and ground serves as the reference for this voltage. Voltage only exists between two points.

This is confusing me because in my mind, for example, radio signals do not need a ground connection. The signal comes and gets read.

Radio signals are photon-based; the oscillation of photons at a given frequency being broadcast from a location are what define the signal. Since frequencies are absolute, they can be discriminated without a (relative) reference.

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  • Even in radio, the signal voltage is the instantaneous antenna voltage referenced to ground.
    – JRobert
    Dec 21, 2014 at 13:49

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