3 ms·

keep in mind I don't know much about waves, so all of this could be wrong, but I think PWM works by modulating the width of the pulse, in other words, the "dura

keep in mind I don't know much about waves, so all of this could be wrong, but I think PWM works by modulating the width of the pulse, in other words, the "duration of the note" if you will, so the frequency of the square wave remains constant. You have a high pulse of width t to represent a zero and a high pulse of t*2 to represent 1. The human ear might hear this as a modulating frequency, but that's only because the pulses are changing faster than our brains can recognize pitch, if that makes any sense . I don't know what a t state is, but I suspect the number is the duration of the pulse in microseconds or something of the sort. I believe IR remotes work on a similar principle: a series of blinks of two different durations, which represent 0 and 1

MobiusHorizons 1y ago
What you are describing is basically CW which is how Morse code is transmitted over radio. It works well at the low data rates of Morse code. The higher the symbol rate, however, the higher resolution you need for measuring pulse length, which requires sharper edges from off to on. In practice it is usually easier to use different tones for each symbol (fsk) since the pulse length is less critical in that case. Quadrature modulation like bpsk is more efficient at the cost of additional complexity, and spread spectrum techniques allow for much better performance in noisy environments at the cost of using more bandwidth. So as usual in engineering, it’s a trade off that has to be decided on a case by case basis.
nomel 1y ago
The spectrum of the shorter pulses would have a higher frequency peak show up, which would also a slightly reduced carrier (PWM frequency) peak. This is why I say it's kinda like FSK: the spectral energy somewhat shifts between two frequencies (well, really a bunch of harmonics). To decode it, with a simple setup, you could just look at the amplitude of the higher frequency peak relative to the carrier peak. In fact, you don't even need the carrier! You can just look for changes in the amplitude of the higher frequency peak.

MobiusHorizons 1y ago

What you are describing is basically CW which is how Morse code is transmitted over radio. It works well at the low data rates of Morse code. The higher the symbol rate, however, the higher resolution you need for measuring pulse length, which requires sharper edges from off to on. In practice it is usually easier to use different tones for each symbol (fsk) since the pulse length is less critical in that case. Quadrature modulation like bpsk is more efficient at the cost of additional complexity, and spread spectrum techniques allow for much better performance in noisy environments at the cost of using more bandwidth. So as usual in engineering, it’s a trade off that has to be decided on a case by case basis.

nomel 1y ago

The spectrum of the shorter pulses would have a higher frequency peak show up, which would also a slightly reduced carrier (PWM frequency) peak. This is why I say it's kinda like FSK: the spectral energy somewhat shifts between two frequencies (well, really a bunch of harmonics). To decode it, with a simple setup, you could just look at the amplitude of the higher frequency peak relative to the carrier peak. In fact, you don't even need the carrier! You can just look for changes in the amplitude of the higher frequency peak.