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I think that is what he was doing. No need to get snooty.please ask questions.
3) The speed of the person divided by the speed of sound in air (about 300 m/s) determines the Doppler shift. The round trip distance for the sound is actually increasing/decreasing at twice the rate of the person's movement. So if the person is moving at 1 m/s the Doppler shift is 2/300. Multiply this figure by 40 kHz and you have a shift (40,000*2/300), about 270 Hz. (1 m/s is probably the fastest you'll see someone move indoors; 0.05 m/s is probably a good lower bound, or 13 Hz.)
I think that is what he was doing. No need to get snooty.
And as I stated, I was not sure about the formula. I found it on the net, it stated C as being speed of light, as wavelength formula is lambda x freq = C (speed of light) I can see the relationship.
Since Doppler works in the electro magnetic spectrum as well as sound. I am sure there may be several ways to calc doppler shift.
Without a filter, the transistor will turn on and turn off exactly like the gate does.
I see where you need more explanation. The XOR is fast and outputs the instantaneous state of the two signals. If the two signals are a different frequency, the waveform at the XOR output will vary between 0 (when the two signals are in phase) and 1 (when they are out of phase). At other times, the output will be 40 KHz of varying duty cycle.I thought the XOR gate only outputed high when inputs differed and remained low when inputs were equal.
Yes, there are many simpler ways... some are very good. I guess I got carried away with the Doppler idea.
You can still use your Usonic devices. Send carrier from TX to RX. If someone walks by RX level drops below a threshold and triggers a person walking by condition.
It would be something like ~~~~~~----~~~~ where the dashes are break in carrier.
It would not be a mere go/no go condition as the soundwaves would be bouncing around, so you would have to look for a drop in RX signal level, rather than 1 or 0.
Something like that. Get what I mean?
But will this work with a setup that has both usonic transducers on the same side? I do not want to have to put one pointing at the other. I want everything to be in one enclosure (one usonic transducer next to the other).
That's why Doppler based detection fascinates me so much.when someone steps inbetween, the signal is interrupted. This is not what I want