hi Marcel, Marcel van Lieshout wrote: >Stef, > >----- Original Message ----- >From: "Stef Mientki" >To: >Sent: Wednesday, November 12, 2003 11:00 PM >Subject: Re: [EE:] GPS vs LPS > > > > >>Marcel van Lieshout wrote: >> >> >> >>>My ultimate goal is a range of at least 5 meters with a repeatable >>> >>> >accuracy > > >>>of 1 millimeter. Yes, I know one should have goals that can be met ;-) >>> >>> >>> >>I like that attitude, ... >>... but ever calculated what the wavelength of a 40 kHz sound wave is ? >>340 m/s , 40 kHz ---> ...... ;-( >>And then I don't even talk about the change of sound speed due to >>temperature and humidity ! >> >> > >Yes, I know that it would be better to choose a higher frequency. I know >that I'm trying to achieve a better accuracy than the wavelength makes >possible. I think it may be possible. > Yes, it's possible, when you're signal to noise ratio is low enough you achieve 0.05 wavelength (I did it once ;-) So that's enough for you. > It's a tradeoff between price, area >coverage, and resolution. The higher the frequency, the better resolution >but the ultrasound travels shorter distances and the transducers are more >costly. For the moment I keep this higher frequency in the back of my head. > >As for the fluctuation in the speed of sound: The beacons are at fixed >positions. Measuring the TOF (time of flight) of the sound between two >beacons at a well known distance let's me calculate the current sound speed. >This measurement is done frequently (eg. once a minute). The result is >(through rf) broadcasted to all interested objects. > Aha, that's a new point (or I missed it), very good. >>>BTW it's my first PIC project (exept for the blinking led thing), even >>>worse: it's my first embedded project. >>> >>> >>> >>And of course you are going to program it in assembler ? >>And program the PIC with a selfmade programmer ? >> >> > >I will write everything in C. Required optimizations might be rewritten in >assembler. BTW I'm a experienced C-programmer. The use of assembly is not >unknown to me (no PIC's though). My programmer is bought, has a usb >connection and is, next to being a programmer, also an ICD. > > Oh that's 'sounds' different, no doubts anymore, you'll probably succeed ! Maybe I can even hear the sound, in the neighboorhood of Nijmegen ;-) >Never said it would be easy... > > I'ld love to see your results ! Stef -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu