highaltitude.log.20070420

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[16:45] <msweeney> afternoon?
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[18:35] <msweeney> evening
[18:40] <edwardmoore> hi
[18:42] <msweeney> I got my GPS this week!
[18:42] <edwardmoore> ooooh
[18:42] <edwardmoore> fun
[18:43] <msweeney> yeah. Well it would be if I could have something to plug it into. Couldn't order from gumstix in the end :|
[18:43] <edwardmoore> hyperterminal on the pc?
[18:43] <edwardmoore> wire it up to the serial port and see what it spits out
[18:43] <msweeney> well there is that, but y'know ;-)
[18:43] <edwardmoore> :)
[18:43] <msweeney> I also need an antenna
[18:44] <edwardmoore> arse
[18:44] <msweeney> they included one, but with the wrong fitting
[18:44] <edwardmoore> which gps did u get?
[18:44] <msweeney> (which they did advertise as such, but its a bit crap)
[18:44] <msweeney> erm Rockwell jupiter
[18:44] <edwardmoore> sounds like a nuclear missile
[18:44] <msweeney> heh almost
[18:45] <msweeney> jcoxon doesn't rate it highly, but itll do for playing for now
[18:45] <edwardmoore> sparkfun are good for gps porn
[18:45] <msweeney> sparkfun?
[18:46] <edwardmoore> sparkfun.com
[18:46] <edwardmoore> it's like heaven
[18:46] <edwardmoore> all the electronic components a tinkerer needs
[18:47] <msweeney> I love the dollar rate at the moment ;-)
[18:47] <edwardmoore> http://www.sparkfun.com/commerce/categories.php?cPath=4_17
[18:48] <edwardmoore> the em-406 is particularly good
[18:49] <msweeney> hrm, does it have a serial connection without having to hack wires to the board?
[18:49] <edwardmoore> yeah it's great :) 1:2 is my kinda language
[18:49] <msweeney> 1:2?
[18:49] <edwardmoore> yes it comes with a 5 pin connector. but you'll have to do some solvering to get it to talk to a gumstix i think
[18:49] <edwardmoore> 1 pound = 2 dollar
[18:51] Action: msweeney apologises for being so slo
[18:51] <msweeney> w
[18:51] <edwardmoore> lol, np :p
[18:51] <msweeney> long day
[18:51] <edwardmoore> yeah. i have to pack in a minute
[18:52] <edwardmoore> heading back tomorrow
[18:52] <msweeney> whereya off?
[18:52] <edwardmoore> where or when?
[18:53] <msweeney> both?
[18:53] <edwardmoore> lol, sorry misread
[18:53] <edwardmoore> uni, tomorrow morn
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[18:53] <msweeney> oh, still off for easter? I've been back a week
[18:53] <msweeney> evening
[18:53] <edwardmoore> yep still off
[18:53] <edwardmoore> but no longer
[18:53] <edwardmoore> hi steve
[18:53] <rocketboy> hi guys
[18:54] <msweeney> that programmer, steve...did you post it to Martin sweeney or Lawrence sweeney? Its not arrived yet, but there is a parcel for someone called lawrence sweeney, who i've never heard of around here
[18:54] <rocketboy> ms - I havn't sent the PIC programmer off yet in case you are wondering
[18:54] <edwardmoore> lol
[18:54] <msweeney> heh fair enough
[18:55] <rocketboy> I'm still serching round for the power supply
[18:55] <msweeney> (I just searched for him on facebook and found him)
[18:55] <msweeney> what cable was it that I needed?
[18:55] <rocketboy> thought I at least test it first to check it still works
[18:56] <rocketboy> you will need a parallel port extender cable - 25way D male to 25way d femaile
[18:57] <msweeney> hrm, not sure if I have one of them
[18:58] <edwardmoore> get that ribbon cable out
[18:58] <rocketboy> yeah - I'll see if I can find one
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[23:40] <Laurenceb> Hi all
[23:41] <rocketboy> hi lb
[23:41] <rocketboy> I had a q to ask
[23:41] <Laurenceb> I'll post off your radio tomorrow
[23:41] <Laurenceb> sorrym was busy with collections
[23:41] <rocketboy> yeah no probs - sounds a bit mashed
[23:42] <Laurenceb> collections=start of term exams
[23:42] <rocketboy> Ah Ok - so here is my Q
[23:43] <rocketboy> with a GPS - it is outputting position, speed and direction one per second (for the 1Hz type)
[23:44] <rocketboy> so when is that - an average over the second or
[23:44] <rocketboy> some point between the two samples
[23:44] <rocketboy> any ideas - based on what you did for the glider?
[23:44] <Laurenceb> for a sirf2, its an average of approx 300ms
[23:45] <Laurenceb> at the start of the period between each "report"
[23:45] <Laurenceb> sent through the serial by nmea
[23:45] <Laurenceb> so as its about 300ms of nmea before we get $GPRMC
[23:46] <rocketboy> yeah - when I guess 80 characters takes about 80ms to send at 9600baud
[23:46] <Laurenceb> we can treat it as lag of 1 second when we get each report of heading into the micros sram
[23:46] <rocketboy> so thats 80ms of the 300
[23:46] <rocketboy> and some time to do the calculations
[23:46] <Laurenceb> well its hard to do the approximation
[23:46] <Laurenceb> I ran back and forth across the street
[23:47] <rocketboy> I have a rate gyro working now - so i was going to try to correlate the two readings
[23:47] <rocketboy> (gyro vs GPS)
[23:48] <rocketboy> also - any idea of a minimum speed for the heading to be accurate?
[23:49] <Laurenceb> wel for sirf2, its +-1 ms^-1
[23:49] <rocketboy> Ah ok thats not too bad
[23:49] <Laurenceb> anything less than 1m/s is treated as zero
[23:51] <rocketboy> I was going to store rate gyro readings (at 10Hz) - then choose a point in time prior to a GPS reading to add them to
[23:51] <rocketboy> so I'll start with 300ms before the reading
[23:51] <Laurenceb> yep, I thought of that as well
[23:51] <Laurenceb> no 1 second, sorry
[23:51] <rocketboy> ??
[23:51] <Laurenceb> I should do a timing diagram
[23:52] <Laurenceb> it takes 300ms for message to come out of gps
[23:52] <Laurenceb> an that was recorded over a period 700ms to 1 second before the nmea string started to be transmitted
[23:52] <rocketboy> ah ok - so the timing point is 1.3 seconds before a message come out?
[23:53] <Laurenceb> yes
[23:53] <rocketboy> Ok thats not too much of a problem
[23:53] <Laurenceb> but the fact its recorded over approx 300ms takes that down to about 1.15 s
[23:53] <rocketboy> only 13 samples
[23:53] <rocketboy> 12
[23:53] <Laurenceb> so for the sake of convenience Id treat it as 1s
[23:54] <Laurenceb> then fiddle about to get it working better
[23:54] <rocketboy> I can start with 10 samples back and try forward and backwards from there for the best match
[23:54] <Laurenceb> yep good plan
[23:55] <Laurenceb> I'd be wary of high rate gps
[23:55] <rocketboy> I'm only planning on using 1Hz
[23:55] <Laurenceb> the antaris I tried was no better than sirf2
[23:55] <Laurenceb> even though it was 4hz
[23:55] <rocketboy> since I have the rate gyro
[23:55] <Laurenceb> there was probably more lag, and overshoot
[23:56] <Laurenceb> looking at the datasheet, it filters it with a kalman filter
[23:56] <rocketboy> there everywhere
[23:56] <Laurenceb> which is not good, we can do that better in the micro
[23:57] <Laurenceb> sirf2 is nice, lag+noise is all there is
[23:57] <Laurenceb> antaris, its a mess
[23:58] <Laurenceb> I was thinking of having the gyro stuff in a timer interrupt
[23:59] <Laurenceb> which would also handle temperature compensation with a look up table
[23:59] <rocketboy> yep - that how mine works more or less
[23:59] <rocketboy> there is an interrupt every 95ms
[00:00] --- Sat Apr 21 2007