highaltitude.log.20100215

[00:07] <MikeMc68> night
[00:11] edmoore|away (~836ff570@gateway/web/freenode/x-sytrpbbzcxuqfjtw) left irc: Ping timeout: 252 seconds
[00:17] <fergusnoble> fixed landing prediction
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[01:12] <SpeedEvil> Tomorrow, I am going to embark on a shitty path loss predictor.
[01:13] <Randomskk> isn't path loss fairly well defined as far as humidity, distance, frequency etc go?
[01:14] <SpeedEvil> yes
[01:14] <SpeedEvil> I meant over terrain
[01:14] <Randomskk> aah, okay
[01:14] <SpeedEvil> so given two lat/lon/alt positions, it looks up elevations and does the sums.
[01:15] <SpeedEvil> It's somewhat hacky as it involves parsing 180M files in awk for every sum.
[01:16] <Randomskk> a lot
[01:17] <Randomskk> does it take long?
[01:18] <SpeedEvil> bout a second on a c2d laptop
[01:18] <Randomskk> nice
[01:18] <SpeedEvil> for some preliminary 'how bad might this be' tests
[01:18] <SpeedEvil> without the actual sums - which are easy
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[08:39] <juxta> MikeMc68, you around
[08:39] <juxta> ?>
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[08:41] <juxta> hi rjharrison
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[08:57] <rjharrison> Hey juxta
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[09:30] <rjharrison> ping edmoore
[09:31] <edmoore> hi
[09:31] <rjharrison> http://www.robertharrison.org/listen/poll.php?callsign=horus&missionid=86&lastid=1
[09:31] <rjharrison> This is the polling script
[09:31] <edmoore> nice
[09:32] <edmoore> (save for newlines! )
[09:32] <rjharrison> If you look at the id and change it at the end it will pull back only new data
[09:32] <rjharrison> Yep I thought about that but this is for machine use so \nl is better than <BR> I'm guessing
[09:33] <rjharrison> I guess it could be processed out the <BR>
[09:33] <edmoore> sure
[09:34] <rjharrison> Any thoughts do you think the BR should be there
[09:35] <rjharrison> missionid=0 or just not there is the current mission
[09:35] <rjharrison> the simplest is http://www.robertharrison.org/listen/poll.php?callsign=atlas
[09:36] <rjharrison> This will give all the data from the current launch for atlas
[09:36] <rjharrison> now technically i should be quite easy to say http://www.robertharrison.org/listen/poll.php?callsign=horus&format=kml
[09:37] <rjharrison> This could then be viewed in google maps
[09:37] <rjharrison> Is there a need for that ?
[09:40] <rjharrison> edmoore I guess this data can be pulled into the predicitor to give continuous predictions for landing
[09:41] <rjharrison> Well say updated every five minutes
[09:41] <edmoore> sure. though the predictor can run pretty fast
[09:41] <edmoore> perhaps once per status packet
[09:41] <rjharrison> 5 seconds fine my me
[09:41] <rjharrison> by
[09:41] <edmoore> 5 mins is a bit slow, especially suring descent when you want really up-to-date data
[09:41] <rjharrison> Yep
[09:42] <rjharrison> Ajax on a google map constantly plotting a new landing spot would be good
[09:43] <rjharrison> This should open the data up. I'm going to add a whole load of fields to this in a bit fixed ones such as temp_int, temp_ext, pressure and custom_1...custom_10
[09:44] <rjharrison> The frixed fields are usefull for comparisons between all launched where data is available
[09:44] <rjharrison> The custome 1-10 can contain what the hell you like
[09:53] <edmoore> right, lectures. going to only be sporadic today
[09:53] Nick change: edmoore -> edmoore|lectures
[09:59] <rjharrison> hey fergusnoble
[09:59] <rjharrison> How are you doing?
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[09:59] <rjharrison> Not well obv. :)
[10:00] <Laurenceb> I've added some stuff to the line of sight calculator
[10:01] <Laurenceb> so you can enter horizon elevation now
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[10:45] <MikeMc68> hey juxta
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[11:01] <juxta> hey MikeMc68, rjharrison
[11:01] <juxta> back now, was making/eating dinner :)
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[11:26] <rjharrison> juxta np
[11:26] <rjharrison> How is it going>
[11:26] <rjharrison> ?
[11:26] <juxta> good good
[11:26] <juxta> still playing around with ideas for this board in eagle
[11:26] <juxta> not sure if I should try to put everything on the one board or perhaps seperate it a bit
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[11:28] <rjharrison> juxta both approaches have adv / diss
[11:28] <juxta> hm
[11:28] <rjharrison> Not much help I know
[11:28] <juxta> I planning on having an AVR for the main processor
[11:28] <rjharrison> :)
[11:28] <rjharrison> My favorite
[11:28] <juxta> and something else which I can offload telem too
[11:29] <juxta> probably just another atmega, but maybe an attiny
[11:29] <rjharrison> the 328p's are cool
[11:29] <rjharrison> Yep the tiny is fine too
[11:29] <juxta> yeah, the 328 is what I have here
[11:29] <rjharrison> I think I'm going that way too something to drive the radio
[11:29] <juxta> that way I can get data etc more frequently
[11:29] <juxta> as it'll be logging to SD
[11:30] <rjharrison> This leaves the avr available for logging and keeping an eye on the sensors
[11:30] <rjharrison> :)
[11:30] <rjharrison> Yep
[11:30] <juxta> I dont have any attinys though
[11:30] <rjharrison> One could ask how often do you need the data logged but I like the approach
[11:30] <juxta> and I dont have an AVR programmer
[11:30] <juxta> so I might just use another 328
[11:30] <rjharrison> AVR programmer = quite cheap
[11:30] <juxta> cause I have lots of them
[11:31] <rjharrison> 328's are cool that's what I have on icarus
[11:31] <rjharrison> icarus III
[11:31] <juxta> rjharrison, yeah, but serial on an attiny is probably going to be a pain, I dont know what the situation with libraries is on those chips
[11:31] <juxta> I've only used the 328 with the arduino libraries
[11:32] <juxta> do you have a photo of icarus III btw? I think I saw one once, it's all SMD, right?
[11:32] <rjharrison> http://www.robertharrison.org/images/various/Icarus%20III%20-%20Breadboard%20Prototype.JPG
[11:32] <rjharrison> That's the prototype
[11:32] <rjharrison> On sec and I'll take a recent picture
[11:33] <Laurenceb_> what pressure senor are you using?
[11:35] <juxta> I was going to ask the same thing :)
[11:35] <rjharrison> http://www.robertharrison.org/svn/filedetails.php?repname=the-icarus-project&path=%2FIcarus+III%2Fdatasheets%2FFreescale-Diff-PSensor-MPXV5004DP.pdf
[11:36] <juxta> ah
[11:36] <juxta> I've been looking at a similar one - the MPX5100D
[11:37] <juxta> yours has a better range though
[11:37] <Laurenceb_> interesting
[11:37] <Laurenceb_> I was thinking of using it for a pitot sensor
[11:38] <Laurenceb_> but decided the drift was too high
[11:38] <juxta> oh wait
[11:38] <juxta> 0-3.92 kPa?
[11:41] <juxta> rjharrison, still about?
[11:42] <rjharrison> yep
[11:42] <rjharrison> http://www.robertharrison.org/images/icarus3/Icarus%20III.JPG
[11:42] <rjharrison> Bit big but this is it
[11:43] <rjharrison> Yep it's a differential pressure sensor
[11:43] <juxta> ah brilliant!
[11:43] <juxta> rjharrison - what's the go with differential sensors, how do they work exactly?
[11:43] <rjharrison> I want to measure the difference between the balloon internal pressure and the local atmos.
[11:43] <juxta> how do you convert that to a useful range?
[11:43] <juxta> ohh
[11:43] <juxta> I okay
[11:43] <juxta> I see*
[11:44] <Laurenceb_> where the pcb from?
[11:44] <rjharrison> Olimex
[11:44] <Laurenceb_> ah
[11:45] <juxta> so you have 5v and 3v3 power onboard I guess rjharrison
[11:45] <rjharrison> Yep
[11:45] <rjharrison> Hence the two power connectors
[11:45] <juxta> and you just send the atmega 5v to the ref voltage pin?
[11:45] <rjharrison> Though they can me linked and powered from a single source
[11:46] <rjharrison> Actually I use a divider to move it down to 3.3v
[11:46] <rjharrison> and ref on 3.3
[11:46] <juxta> ah okay
[11:46] <juxta> is there a limitation that stops you from using 5v as the reference voltage?
[11:47] <rjharrison> Yep
[11:47] <juxta> or is the divider for simplicities sake?
[11:47] <rjharrison> Vref can't me more than 0.3 Vcc IIRC
[11:47] <rjharrison> http://www.robertharrison.org/svn/filedetails.php?repname=the-icarus-project&path=%2FIcarus+III%2Feagle%2FIcarus+III%2FIcarus.pdf
[11:48] <rjharrison> Right I need to feed my kids back in a bit
[11:48] <Laurenceb_> whats vref?
[11:57] <Laurenceb_> http://media.armadilloaerospace.com/2009_11_03/2009_11_03_2959_ft_boosted_hop.wmv
[11:57] <Laurenceb_> ^ nice
[12:01] <MikeMc68> WOW!!
[12:20] <rjharrison> boo
[12:24] Action: SpeedEvil wants one.
[12:30] <juxta> whoa, that's nice
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[12:33] <juxta> Laurenceb_: where is that?
[12:48] <Laurenceb_> texas
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[12:56] <Laurenceb_> bbl
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[13:03] <rjharrison> Hey juxta you still outthere
[13:03] <juxta> sure am
[13:05] <rjharrison> Been playing with extracting data from the listener
[13:05] <juxta> ah right, with the socket?
[13:05] <rjharrison> I'm hoping to be able to allow people to pull data into there own apps
[13:05] <rjharrison> Well via http atm
[13:06] <rjharrison> for example
[13:06] <juxta> oh, from the listener, i see, I thought you meant fldigi :)
[13:06] <rjharrison> http://www.robertharrison.org/listen/poll.php?callsign=horus&missionid=86&lastid=61937&format=html
[13:06] <juxta> yeah I saw a big page of coords before
[13:06] <rjharrison> This is your flight data
[13:06] <juxta> ahh, nice :D
[13:07] <rjharrison> There is a bit of early data in there which I need to pull out
[13:07] <rjharrison> If you pass in a lastid you will only get more recent data back than your last id
[13:07] <rjharrison> Does that make sense?
[13:07] <rjharrison> the id is the first column
[13:07] <juxta> yep
[13:08] <rjharrison> http://www.robertharrison.org/listen/poll.php?callsign=horus&missionid=86&lastid=62550&format=html
[13:08] <rjharrison> This gives teh last 10 ish data points
[13:08] <juxta> yeah
[13:08] <juxta> what's the ID? just a sequential number?
[13:08] <rjharrison> Yep
[13:09] <rjharrison> Given by the server
[13:09] <juxta> ah right
[13:09] <juxta> it would be handy to have a way to grab say the most recent 5 packets etc
[13:09] <SpeedEvil> If I take two lat/lon pairs - if I take a point x% along each difference between lat-lon - does this describe a great circle?
[13:11] <rjharrison> Yep good point
[13:11] <juxta> hey rjharrison - why did you omit the mounting holes on icarus 3? didn't end up using them?
[13:11] <rjharrison> Will work on that too
[13:12] <rjharrison> juxta yep I never used them
[13:12] <juxta> I'm thinking I probably wont use mounting holes either, so I'll forgo them I think
[13:12] <rjharrison> You can't mount to polystyreene very easily
[13:13] <rjharrison> Sure you could stick sime balsa wood in there but I quite like to take the board in and out
[13:13] <juxta> also - that ham Adrian who's been helping me has a bunch of etching gear, a lighbox to expose boards, might give it a shot and see if I can make it manually - just gotta drill all the holes after
[13:13] <juxta> yeah, I'd rather just wedge it in with a bit of foam or something
[13:14] <rjharrison> Yep the word fuck that come to mind :)
[13:14] <juxta> btw - what sort of filter do you use in front of your cam?
[13:14] <rjharrison> But go for it
[13:14] <juxta> haha
[13:14] <rjharrison> Just a uv filter
[13:14] <juxta> yeah it seems a little tedious
[13:14] <juxta> a decent hoya? or just a cheapo?
[13:14] <rjharrison> I would like to remove some blue light (haze) too
[13:14] <rjharrison> Perhaps a blue filter on a launch in the future
[13:15] <juxta> I used a $5 ebay job on mine, i'm thinking it may not have helped with the reflections of the cam itself
[13:15] <rjharrison> All the pictures come back very blue to me
[13:15] <rjharrison> I think flush with He next time and put less He in the balloon You'll get the pics you want
[13:15] <rjharrison> A hoya
[13:15] <juxta> yeah
[13:16] <juxta> either that or leave the cam open to the atmosphere I guess
[13:16] <rjharrison> It was clearing nicely just b4 burst
[13:16] <juxta> yeah it was, bit of a shame :(
[13:16] <rjharrison> You going to launch again soom?
[13:16] <rjharrison> Son
[13:16] <rjharrison> Soon even
[13:17] <juxta> hoping to
[13:17] <juxta> might make up a payload tomorrow if I have some time
[13:17] <rjharrison> Ooh
[13:17] <juxta> no photos on this one I dont think, just a small one
[13:17] <rjharrison> Tracker then
[13:17] <juxta> yeah
[13:17] <juxta> tracker for sure
[13:18] <rjharrison> Be interesting to see if you can resist the temptation to send the camera
[13:18] <rjharrison> I have done one launch without so far
[13:18] <juxta> I think I will also put something with CHDK onboard in next time
[13:18] <juxta> triggering manually is a bit of a pain, also you dont have the option for video etc so easily then
[13:18] <rjharrison> Yep that is cool and even better you can control the camera via USB pulses
[13:19] <juxta> yeah that would be cool
[13:19] <juxta> I'll see if my friend will sell me his a570 :)
[13:20] <juxta> rjharrison - did you get your board layout right first time around? or did you have to have it re-made at all to fix errors?
[13:21] <rjharrison> Well there is one error on the pcb but yep right first time
[13:21] <rjharrison> But build a prototype
[13:21] <juxta> will do
[13:22] <juxta> what error is there?
[13:22] <rjharrison> I was missing an R to ground
[13:22] <rjharrison> But I fixed it by soldering one to a GND via and the point where I need it
[13:23] <juxta> ah okay
[13:23] <juxta> did you manually route yours boards too?
[13:23] <rjharrison> Back to the F that
[13:23] <rjharrison> edmoore|lectures swares by it and he's right
[13:24] <juxta> yeah natrium was telling me not to autoroute too, haha
[13:24] <rjharrison> But I just manual route the bits I don't like and let autorouter to the rest
[13:24] <juxta> that's what i've been doing so dar also
[13:24] <juxta> far*
[13:24] <rjharrison> Life is too short
[13:25] <rjharrison> I used a groun plane on this board which is a good thing I believe
[13:26] <rjharrison> You can see the fix on the image top left of the atmega chip there is an R at an angle
[13:27] <juxta> yeah, and it looks like a resistor/cap soldered in at a funny angle?
[13:28] <rjharrison> Yep R
[13:29] <rjharrison> Lucky the via was there
[13:29] <juxta> hehe
[13:29] <rjharrison> This pulls the current off the FET to allow it to turn off again
[13:29] <juxta> did you solder the atmega by hand?
[13:29] <rjharrison> I fixed the design file though
[13:30] <rjharrison> There are a few other things I want to do. Like break out the rest of the pins
[13:31] <juxta> I'm thinking I'll do that also
[13:33] <juxta> rjharrison, I bought a couple of ublox modules to use by the way
[13:39] <rjharrison> Cool JC rate them and I like them too
[13:39] <rjharrison> Exp that one with the antenna on it
[13:40] <juxta> this is the one I got:
[13:40] <juxta> http://www.esawdust.com/product/egps-fsa03-module/
[13:47] <rjharrison> Very nice
[13:47] <rjharrison> I want one of those :)
[13:48] <rjharrison> The lassen is fine but that has everything on it
[13:49] <juxta> yeah
[13:49] <juxta> well priced too
[13:49] <rjharrison> Yep very its 40 quid here in the uk
[13:53] <juxta> hmm
[13:53] <juxta> the autorouter seems to fail on some very trivial things
[14:00] <juxta> rjharrison, if you're still there, what's the part name for those screw terminals in eagle?
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[14:23] <rjharrison> Ahh I made them
[14:23] <rjharrison> They are in my eagle file in the svn
[14:28] <rjharrison> ping juxta
[14:28] <juxta> cheers rjharrison
[14:29] <rjharrison> Paste this into the google map search box
[14:29] <rjharrison> http://www.robertharrison.org/listen/poll.php?callsign=horus&missionid=86&format=KML
[14:29] <juxta> nice work :)
[14:30] <juxta> in hindsight we were pretty luck that didn't cross the river before landing
[14:30] <juxta> lucky* even
[14:31] <juxta> there are only 2 places cars can cross - Murray Bridge (south), or Mannum (north)
[14:35] <rjharrison> Ooh
[14:35] <rjharrison> Lucky
[14:36] <rjharrison> This will allow us to some fun things with the data in the future hopefully
[14:39] Nick change: edmoore|lectures -> edmoore
[14:40] <rjharrison> Yo edmoore
[14:40] <rjharrison> polling working now
[14:41] <rjharrison> if you paste this into google maps you will get the path of horus http://www.robertharrison.org/listen/poll.php?callsign=horus&missionid=86&format=KML
[15:05] <rjharrison> edmoore et al http://ukhas.org.uk/projects:dlistener#server
[15:06] <rjharrison> New info about getting data from the server via http
[15:11] <edmoore> ok cool, awesome work
[15:11] <edmoore> sorry for being unresponsive btw, just in the lab doing project
[15:17] <rjharrison> edmoore np
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[16:10] <Lunar_Lander> hello
[16:11] <rjharrison> hi Lunar_Lander
[16:11] <rjharrison> ping ei7ig ei7ig_laptop
[16:12] <rjharrison> You have left your pc on still running fldigi if you havn't realised :)
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[16:32] <ei7ig_laptop> hi rjharrison
[16:32] <ei7ig_laptop> was in a meeting.
[16:32] <ei7ig_laptop> yup. I was using it for CW decoding this morning before I came to work.
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[16:55] <Lunar_Lander> hello again
[16:55] <MikeMc68> hi
[16:55] <Lunar_Lander> laptop simply shut down
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[17:49] <Lunar_Lander> hi jcoxon
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[17:50] <jcoxon> hey Lunar_Lander
[17:51] <Lunar_Lander> how's life?
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[17:55] <rjharrison> Ping jcoxon
[17:55] <jcoxon> hey rjharrison
[17:55] <jcoxon> Lunar_Lander, not bad thanks
[17:55] <rjharrison> ei7ig have you turned off your fldigi?
[17:55] <rjharrison> jcoxon you got 5 4 a call
[17:55] <Lunar_Lander> mine too
[17:56] <jcoxon> rjharrison, yup
[17:56] <rjharrison> Skype or normal
[17:56] <Lunar_Lander> I tried out BalloonTrack by EOSS
[17:56] <Lunar_Lander> it also looks interesting as a prediction program
[17:57] <rjharrison> jcoxon skype or normal
[17:58] <jcoxon> skype is no problem
[17:59] <hsmith> Hi James
[18:00] <jcoxon> ?hello hsmith
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[18:55] <Hiena> 'evening!
[18:55] <Hiena> How the thing goes up?
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[19:16] <jcoxon> hey Hiena
[19:16] <jcoxon> evening edmoore
[19:16] <edmoore> hi
[19:17] <jcoxon> fully recovered from the ball?
[19:17] <edmoore> yep thanks
[19:17] <edmoore> was fine on sat
[19:17] <edmoore> berocca is the key
[19:19] <jcoxon> :-)
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[19:53] <rjharrison> Evening all
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[20:05] <Lunar_Lander> evening rjharrison
[20:06] <rjharrison> hehe
[20:06] <rjharrison> Hows it going
[20:06] <Lunar_Lander> fine and you?
[20:06] <rjharrison> Yep looking forward to getting my own payload up again
[20:06] <Lunar_Lander> nice
[20:07] <Lunar_Lander> I have a physics exam tomorrow
[20:07] <rjharrison> oooh
[20:07] <edmoore> Lunar_Lander: bad luck :(
[20:07] <edmoore> what sort of stuff is it on?
[20:08] <rjharrison> edmoore do I need to liase with anyone re the polling of data
[20:08] <edmoore> probs not. or at least, no one else is organized enough to through cycles at it yet :)
[20:08] <edmoore> brain cycles, that is *
[20:08] <rjharrison> hehe ok cool
[20:09] <rjharrison> Basically the data is there and ready now for use in a real time predictor
[20:09] <Lunar_Lander> it is Experimental Physics 1
[20:09] <Lunar_Lander> so it is mechanics and some thermodynamics
[20:10] <rjharrison> Given most sentences take 30 seconds to come in I woudl suggest an initial poll of 60 secons
[20:11] <edmoore> Lunar_Lander: i don't enjoy you. I was never much good at either mechanics or thermodynamics
[20:12] <edmoore> s/enjoy/envy
[20:12] <Lunar_Lander> yes
[20:12] <Lunar_Lander> I wonder how it will be
[20:12] <Lunar_Lander> they'
[20:13] <Lunar_Lander> they'll give 10 tasks, each worth 12 points
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[20:13] <Lunar_Lander> and 36 are required to pass
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[20:32] <Laurenceb_> hello
[20:32] <SpeedEvil> Hello_.
[20:32] <Laurenceb_> hi SpeedEvil_
[20:33] Action: SpeedEvil just found out his phone won't get a wifi signal in the oven.
[20:33] <SpeedEvil> (I was pondering using it to observe bread rising.
[20:33] <Laurenceb_> I was looking at anemometer stuff some more - the vishay 0603 pt100 is made of alumina
[20:33] <Laurenceb_> heh
[20:33] <SpeedEvil> On balance it was probably a silly idea.
[20:33] <SpeedEvil> alumina and win!
[20:33] <SpeedEvil> interesting.
[20:34] <Laurenceb_> the conductivity/heat capacity figure is very good
[20:34] <Laurenceb_> compared to the glass the leaded sensors use
[20:34] <SpeedEvil> What is the roder of magnitude if you use something crap - say a solid 0603 thermistor
[20:34] <SpeedEvil> Have you done the numbers for that?
[20:34] <Laurenceb_> yes
[20:34] <Laurenceb_> its works ok just stuck on a pcb
[20:34] <Laurenceb_> ~15hz bandwidth
[20:35] <Laurenceb_> but you need to surround it with a ground plane to mop up the stray heat
[20:35] <SpeedEvil> hmm
[20:35] <Laurenceb_> the tricky bit is getting accuracy and reducing power consumption
[20:35] <SpeedEvil> possibly time to try a pcb with several approaches on.
[20:35] <SpeedEvil> and see which works best
[20:35] <Laurenceb_> yeah
[20:36] <SpeedEvil> how much are the 0603 pt100s?
[20:36] <Laurenceb_> £1.49 in single unit
[20:36] <SpeedEvil> not bad at all
[20:37] <SpeedEvil> are there any thin-film thermistors?
[20:37] <SpeedEvil> but I suppose savings once you get at that level are pointless mostly
[20:37] <Laurenceb_> thermistors tend to have poor tolerance
[20:37] <SpeedEvil> at least for a first run
[20:37] <Laurenceb_> compared to pt100
[20:37] <SpeedEvil> yeah - but if you're servoing the resistance, you don't care
[20:37] <Laurenceb_> also nonlinear
[20:38] <Laurenceb_> you want to keep it x degrees above air temperature ideally
[20:38] <Laurenceb_> not at just x degrees
[20:38] <SpeedEvil> ah
[20:38] <Laurenceb_> that way the heat loss by conduction through the pcb is constant
[20:38] <SpeedEvil> I see.
[20:39] <Laurenceb_> at the moment I'm thinking two pt100 sensors in a bridge with high tolerance resistors
[20:39] <Laurenceb_> or a 0401 resistor with a mini thermocouple glued onto the bottom
[20:40] <Laurenceb_> the second approach gives really low current draw
[20:40] <Laurenceb_> <1ma @3.3v
[20:40] <SpeedEvil> hmm
[20:40] <SpeedEvil> but is fiddly
[20:40] <Laurenceb_> yes
[20:40] <SpeedEvil> easy if you have a nice little machine making 100k of them
[20:41] <SpeedEvil> noit so much if you're swearing at it under a microscope
[20:41] <Laurenceb_> with two pt100 sensors I'm worried about resistor drift
[20:43] <Laurenceb_> the delta temperature is limited by how much current you can use
[20:43] <Laurenceb_> about 1K/ma @3.3v in the 0 to 15m/sec airspeed range
[20:43] <SpeedEvil> presumably at some point they'll get nonlinear - due to assymetric heating
[20:44] <Laurenceb_> pt100 is about 3100ppm/K
[20:44] <Laurenceb_> so say 10K is the delta T, thats 3.1%
[20:44] <Laurenceb_> so you need at least 0.1% resistors for decent performance
[20:45] <SpeedEvil> why
[20:45] <Laurenceb_> and I'm not sure how much they drift
[20:45] <SpeedEvil> if you've got a micro uin there
[20:45] <SpeedEvil> in
[20:45] <Laurenceb_> yeah you can calibrate
[20:45] <Laurenceb_> but resistors drift as they age
[20:45] <SpeedEvil> but you can calibrate that out if you have a zero wind mode surely?
[20:46] <Laurenceb_> maybe, ideally you want a few calibration points
[20:47] <Laurenceb_> I was just thinking thermocouple avoids these problems entirely
[20:47] <SpeedEvil> thermocouples have their own issues of course
[20:48] <Laurenceb_> at least its measuring temperature difference directly
[20:48] <Laurenceb_> you can calibrate out the nonlinearity using a micro with an onboard temp sensor
[20:48] <SpeedEvil> yeah
[20:48] <Laurenceb_> and use published results
[20:48] <Laurenceb_> avoiding the need to calibrate by hand
[20:49] <Laurenceb_> use one of the AD opamps and you can get good results at <0.1K delta temperature
[20:50] <Laurenceb_> 5nv/C bias drift ftw
[20:50] <SpeedEvil> I suspect dissimilarity in your circuit junctions may annoy you more than the opamp drift
[20:51] <Laurenceb_> yes
[20:51] <SpeedEvil> Anyway - going to sleep for a bit. Good luck.
[20:51] <Laurenceb_> another idea is a single pt100 and a micro with onboard temp sensor
[20:51] <Laurenceb_> cya
[20:52] <Lunar_Lander> are you discussing electric thermometers?
[20:52] <Laurenceb_> anemometers
[20:52] <Laurenceb_> for measuring uav airspeed
[20:52] <Laurenceb_> accurately at low speeds <10m/s
[20:53] <Laurenceb_> and over large temperature ranges - its an interesting problem
[20:53] <Laurenceb_> theres no neat solutions avaliable atm
[20:53] <Laurenceb_> so I'm trying to build one
[20:56] <Lunar_Lander> ah
[20:56] <Laurenceb_> basically a hot something or other gets cooled by the airstream, you try to keep it at x degrees above the air temperature, and measure the power required
[20:56] <Laurenceb_> kings law is roughtly that P=A+Bv^0.45
[20:57] <Laurenceb_> where A represents loss by conduction away from the element into its supports, and v is the stream velocity
[20:57] <Lunar_Lander> yeah
[20:57] <Laurenceb_> A and B are constant
[20:57] <Lunar_Lander> yes
[20:57] <Laurenceb_> so you solve for v
[20:57] <Lunar_Lander> yeah
[20:59] <Laurenceb_> the obvious solution is hot wire sensors but they are fragile and a pain to make, so I'm trying to design something that fits completely on a pcb
[21:00] <Laurenceb_> but you have to optimise for low power, fast response, low cost, small size, easy to build, and rejects air temperature changes
[21:00] <Laurenceb_> which is _hard_
[21:00] <Lunar_Lander> yes
[21:00] <Lunar_Lander> I can imagine that
[21:02] <Laurenceb_> if the pcb is embedded in the wing say, with just a 0603 or 0402 surrounded by ground plane, then by heating the component to some temperature above the ground plane and measuring the power required you can apparently get good results
[21:03] <rjharrison> edmoore can you remember the fat library for avr?
[21:03] <rjharrison> ans in bloatware ans dos it's the same thing :)
[21:03] <rjharrison> as
[21:03] <Laurenceb_> * 0603 or 0402 surrounded by ground plane protruding on the upper side
[21:03] <Laurenceb_> rjharrison: elm-chan?
[21:04] <Lunar_Lander> good night
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[21:06] <rjharrison> Laurenceb_ perhaps a bit mor avr specific
[21:06] <rjharrison> eveing jcoxon
[21:06] <jcoxon> evening
[21:06] <Laurenceb_> rjharrison: he has example code
[21:06] <Laurenceb_> hi jocoxon
[21:07] <Laurenceb_> er jcoxon
[21:11] <rjharrison> Laurenceb_ Thanks for that looks just the ticket for writing to my sd card
[21:11] <rjharrison> Humm actually might be a bit big
[21:11] <rjharrison> Thinking atmega328p here
[21:12] <rjharrison> + my code
[21:23] <Laurenceb_> yeah
[21:23] <Laurenceb_> but fat is rather big
[21:24] <rjharrison> I need lean mean fat. Perhaps just wrtingot an existing file that is the cheap way iirc
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[21:39] <rjharrison> Hi fergusnoble
[21:39] <rjharrison> I just missed you this morning
[21:40] <rjharrison> Hope all is well
[21:40] <rjharrison> I have been working on a way to export data from the listener to pump to the predictor for auto landing update
[21:41] <rjharrison> http://ukhas.org.uk/projects:dlistener#server
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[22:05] <rjharrison> ping RocketBoy
[22:06] <rjharrison> Just read your email and funnily enough JC and I just agreed to put CRC in place
[22:10] <junderwood_> Is this the one we used last December or a new one?
[22:16] <MikeMc68> evening
[22:40] ei7ig_laptop (~j0n@2001:770:132:dead:217:f2ff:fec4:58a4) left irc: Quit: Probably gone asleep
[22:42] <Laurenceb_> http://www.taosystem.com/products/LAS.html
[22:44] <SpeedEvil> Laurenceb_: I suppose condensation is really bad?
[22:44] <Laurenceb_> yeah but you probably wont be flying in those conditions
[22:45] <Laurenceb_> oh wow
[22:45] <Laurenceb_> http://www.google.co.uk/url?sa=t&source=web&ct=res&cd=9&ved=0CCMQFjAI&url=http%3A%2F%2Fwww.aeroindiaseminar.com%2FFeedback-pdf_Speakers.aspx%3Fcid%3D21&ei=7815S7bdL4bw0wT2-smtCg&usg=AFQjCNHhQk-Ejx_UNaUM4dB6YRYOEpXwtA
[22:45] <Laurenceb_> page 4
[22:45] <Laurenceb_> freaking awesome
[22:46] <SpeedEvil> how large is it?
[22:47] <Laurenceb_> Fig 1.1
[22:48] <SpeedEvil> ah - loaded
[22:48] <Laurenceb_> Fig3 is epic
[22:48] <Laurenceb_> never mind alloy wheels, thats what I want on my car
[22:49] <Laurenceb_> UAV launcher
[22:49] <SpeedEvil> :)
[22:50] <Laurenceb_> " there is no safety standard for UAV design and operation" lol
[22:52] <Laurenceb_> SpeedEvil: I think I overestimated metal film resistor drift with aging
[22:52] <Laurenceb_> 0.01% is possible cheaply, not 0.1%
[22:52] <SpeedEvil> :)
[22:53] <Laurenceb_> if 10ma or so current isnt bad, then pt100 is probably easiest
[22:53] <Laurenceb_> the vref and ADC on avr is pretty good - around 0.1%
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[22:56] <jcoxon> ping rjharrison
[22:56] <Laurenceb_> the resistors in the bridge need to be pretty good as the temp coefficient for pt100 leads to a shift of only about 3%
[22:56] <SpeedEvil> that's quite high
[22:56] <SpeedEvil> good resistors aren't that much
[22:56] <Laurenceb_> yeah
[22:56] <Laurenceb_> but 0.1% resistor shift would be a significant error
[22:57] <jcoxon> fail whale on twitter!
[22:57] <Laurenceb_> so it needs pretty decent metal film
[22:57] <SpeedEvil> Laurenceb_: surely only in speed?
[22:57] <SpeedEvil> Laurenceb_: I mean appearing as a constant ratio in speed
[22:57] <Laurenceb_> well itd be a bias drift
[22:57] Action: SpeedEvil thinks
[22:57] <SpeedEvil> oh - no
[22:57] <SpeedEvil> it's nonlinear isn't it.
[22:57] <Laurenceb_> as the delta T would be different
[22:58] <Laurenceb_> so the power draw would change
[22:58] <Laurenceb_> P=A+Bv^0.45
[22:58] <Laurenceb_> A and B are constants that are related to delta temperature
[22:58] <Laurenceb_> P is power
[22:58] <SpeedEvil> how are you doing the sensing again?
[22:59] <Laurenceb_> keeping temperature of the 0603-air temperature constant
[22:59] <SpeedEvil> I wondered about something simple - PWM them directly across the supply
[22:59] <Laurenceb_> then measuring the power use in mw
[22:59] <Laurenceb_> P=power
[22:59] <SpeedEvil> then measure impedence during off-time
[22:59] <Laurenceb_> v=air velocity
[22:59] <Laurenceb_> yeah, thats my idea too
[23:01] <SpeedEvil> what about something simple - apply pwm of K to first, 2K to second, measure the delta-t
[23:01] <SpeedEvil> oh - right - constant temp
[23:02] <Laurenceb_> gpio -> 100ohm -> adc -> pt100_cold - > adc/pwm -> pt100_hot ->gnd
[23:03] <Laurenceb_> when the pwm is off, apply vcc to the first gpio for a very short time and measure the voltages, then tristate it
[23:04] <SpeedEvil> hmm
[23:04] <Laurenceb_> adjust the pwm to keep the delta temperature constant
[23:05] <Laurenceb_> then work out the power input
[23:06] <Laurenceb_> and apply the equation to find airspeed
[23:08] <SpeedEvil> http://www.popularmechanics.com/technology/industry/1612252.html
[23:08] <SpeedEvil> (unrelated)
[23:08] <SpeedEvil> sounds sane
[23:09] <Laurenceb_> need to make the adc a little noisy to reduce effect of quantisation
[23:10] <SpeedEvil> not normally a problem
[23:13] <Laurenceb_> http://electronicdesign.com/content.aspx?topic=low-power-thermal-airspeed-sensor6292&catpath=components
[23:13] <Laurenceb_> ^ a good explanation
[23:14] <SpeedEvil> I get the idea.
[23:17] <Laurenceb_> thats actually quite impressive performance for the parts used
[23:17] <SpeedEvil> yup. It's potentially quite simple
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[23:26] Action: Laurenceb_ zzzz
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[00:00] --- Tue Feb 16 2010