dtmf mod

[Dr_Doggy]

hey, eariler i was asking about using 2 antennas to track an fm source, problem is that rf travells too fast, so iv been thinking about using a dtmf encoder and decoder, but then bump the clock up to 40mhz (40xhigher), my thinkin is that then the dtmf sound would hit the khz range so it wouldnt be as annoying as hearing those touch tones,

i could then track the slower sound waves using propegation and volume levels for distance


would this work?

 

[Mr RB]

Well...
1) DTMF sounds in the "KHz range" would probably be even more annoying, unless you want to go ultrasonic.

2) It probably won't work as most of the DTMF decoder chips use analogue notch filtering internally to "decode" the actual frequencies used in the DTMF signal, so bumping up the chip clock xtal would probably just cause a fail.

If you want to build a tracking device it's best to start a thread stating all the things you need; ie range, size, power levels, type of use etc.

 

[Dr_Doggy]

well i was thinking of dtmf so that way i dont need to worry so much about filters, and random noise triggers, i just heard that it was ok as long as you matched the clocks, maybe from 3 mhz to 40mhz IS too much , i figure faster is better since i would do just a few pulses every few seconds, enough time for the device to receive the ping, id even be happy with a cricket sound, i dont think i want to use ultrasound since the waves are linear, and to just detect range by how loud it is, after differentiating the direction
i was hopeing to use piezo, since they are small cheap and light,
https://www.ebay.ca/itm/15-20mm-BRA...551?pt=LH_DefaultDomain_0&hash=item1c27f77ebf
but i looks like those are specific to a 6khz band, which may not work?

as for range and size i always like simple solutions, already packaged ic's if i can, they dont need to go far, nothing more than a bluetooth would, say 50-100 ft,

it could to help cut a step out if i could triangulate on a bluetooth signal itself, but like i was told, rf travels too fast to capture,

 

[audioguru]

An FM radio has the same volume level if the received signal is very strong or if it is fairly weak so volume level cannot be used with two receivers for direction finding.

 

[Dr_Doggy]

yah, thats why i want to do it on audio waves,

 

[audioguru]

Sound waves and radio waves are completely different.
Sound waves operate at a low frequency and travel much much slower than radio waves.
Sound waves do not go far. Radio waves go very far.

Your ears can hear the delay of a sound between your ears and different amplitudes at your ears then your brain determines the direction of a sound. You can't easily do that with radio waves. Your DTMF will be modulating a radio wave and is not a sound.

 

[Dr_Doggy]

YA, so what is the easiest way to do that with sound waves for a pic uc robot?

 

[audioguru]

With sound waves you can have two microphones spaced apart. A circuit detects which mic receives the sound first (sound travels about 768 miles per hour) and/or which mic receives the highest amplitude.
The sounds must be fairly close to the microphones or echoes will mess up the sensing.

 

[Dr_Doggy]

OK i think i would like to try that, if i space my "ears" at say 10 cm aprart, 34332cm/s so thats about 300us to travel from one ear to the other, 8mhz pic should be able to differ that,

what circuit would be good as the detector, also maybe i should think about filtering the audio to just a small f-response?

I was also thinking about the problem with echo, and maybe do a latch, hardware or software, so that after it gets the signal once it will stop listening, with one ear, then count delay to the second ear, then lock the second ear, so all echos are then ignored, untill software calls a reset to start listening again... ?

 

[Mr RB]

Duck quacks don't echo. I saw it on Mythbusters.

 

[audioguru]

Google has details for hundreds of circuits that work properly that you are just guessing about. Most use a digital signal processor (DSP) for speed and three microphones 120 degrees apart so they can sense a sound from any direction.

 

[Dr_Doggy]

YES, but i dont know what a good google circuit would be, or wat to search for) or which would work for me,, i just learned about pll's for decoding frequencies, that would be cool cos then i could read the frequency as an analog value


the dsp's i found i think are a little advanced for me an prolly expensive, plus i can't do surface mounts.

really im just thinking of something simple here