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. 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. > > >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. > Never said it would be easy... > > Stef > > -- > http://www.piclist.com hint: To leave the PICList > mailto:piclist-unsubscribe-request@mitvma.mit.edu > -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu