highaltitude.log.20091113

[00:00] --- Fri Nov 13 2009
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[10:34] <juxta> evening all
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[11:21] <rjharrison> hey juxta
[11:21] <rjharrison> Hows it going
[11:21] <rjharrison> The weekend was fun with the tracker going
[11:21] <rjharrison> Will have to do another launch soonish.
[11:38] <juxta> nice rjharrison - what sort of launch?
[11:42] <russss> I was watching it on my iphone, it worked surprisingly well
[11:51] <rjharrison> russss cool
[11:51] <rjharrison> juxta The next launch will be an experimental one
[11:52] <juxta> rjharrison: world record attempt?
[11:52] <rjharrison> using 869Mhz and 434Mhz both TX
[11:52] <juxta> ah, right
[11:52] <rjharrison> juxta Def. if the wx(weather) is good
[11:52] <rjharrison> January / February for that
[11:53] <rjharrison> PIng RocketBoy
[11:53] <juxta> for altitude? or for an atlantic crossing?
[11:54] <rjharrison> Altitude
[11:54] <russss> ah cool, I can try and decode the 869 with my USRP :)
[11:54] <rjharrison> The atlanic crossing may well kick off around then too
[11:54] <rjharrison> USRP ?
[11:54] <rjharrison> http://www.lprs.co.uk/product_info.php?products_id=109
[11:54] <rjharrison> RocketBoy ^^^^^^^
[11:54] <russss> http://en.wikipedia.org/wiki/Universal_Software_Radio_Peripheral
[11:55] <rjharrison> hey russss that should do it
[11:56] <russss> I only have the 800MHz-2.4GHz daughterboard so I can't pick up the 434
[11:57] <russss> although I really should have bought the 50-870MHz too :P
[11:57] Action: SpeedEvil passes russss a 400MHz oscillator, and a diode mixer
[11:57] <russss> lack of time ;)
[11:57] <russss> I want to try and replicate the decoder using GNU Radio too
[12:01] <russss> it's quite cool: http://www.joshknows.com/images/grc/grc_dial_tone.png
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[12:17] <MikeMc> sfternoon
[12:21] <rjharrison> Hi MikeMc
[12:22] <rjharrison> MikeMc did you manage to track at the w/e?
[12:24] <MikeMc> Your launch?
[12:24] <MikeMc> Yes I did - Which surprised me considering I had an indoor whip in a room facing South plus I was 120km away
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[12:41] <Laurenceb> hi
[12:44] <MikeMc> hi
[12:51] <rjharrison> MikeMc yep radio is magic
[12:51] <rjharrison> When you consider that there are only 4 AA batteries and the comms distance is phenominal
[12:52] <MikeMc> The signal was very noisy - but fldigi decoded it reasonably OK
[12:52] <MikeMc> with the antenna mounted outside on the roof and with a clear view North it would have been much cleaner
[12:54] <rjharrison> Yep I can listen in from up here quite easily
[12:54] <rjharrison> Esp. with the Yagi
[12:54] <rjharrison> I'm going to have a shot on 869Mhz soon and see how that goes
[12:55] <MikeMc> that should be interesting
[12:55] <MikeMc> to see how the distance/power ratio compares to the 433MHz equipment
[12:56] <rjharrison> It will make the antenna alot smaller on the payload too
[12:56] <MikeMc> yeah
[12:56] <Laurenceb> with a yagi it wont be as good
[12:56] <Laurenceb> but the antenna will be smaller and you can use more power
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[12:58] <rjharrison> Laurenceb why won't it be as good with a yagi?
[12:58] <rjharrison> Hey Randomskk
[12:58] <rjharrison> Hey RocketBoy
[12:58] <RocketBoy> yo
[12:58] <Laurenceb> rjharrison: free space loss
[12:58] <rjharrison> http://www.lprs.co.uk/product_info.php?products_id=109
[12:59] <rjharrison> RocketBoy this looks like it might do the business
[12:59] <Laurenceb> yeah thats not going to match 434
[12:59] <rjharrison> Laurenceb The Tonna does that for me
[12:59] <RocketBoy> yeah - I had seen this but we could really do with one a bit longer
[13:00] <rjharrison> But 10 db is not too bas
[13:00] <rjharrison> d
[13:00] <rjharrison> I agree a one meter on would be nice
[13:00] <RocketBoy> like Laurence is saying free space path loss is higher on 868 - so you need to compensate with more antenna gain
[13:00] <rjharrison> Hence the 1m
[13:02] <RocketBoy> yeah - http://www.lprs.co.uk/product_info.php?cPath=3&products_id=108 will be approximatly the same gain as the 1m ones we use on 434
[13:03] <RocketBoy> A one meter long 868MHz will be about 3db up on that
[13:03] <RocketBoy> (assuming its been designed right)
[13:04] <Laurenceb> 868 has the advantage you can use higher power
[13:04] <Laurenceb> also there are some interesting chip antenna for 868
[13:04] <russss> will the higher power compensate for the free space loss then?
[13:04] <Laurenceb> you could experiment with some micro trackers
[13:04] <Laurenceb> easily as you can go up to 500mw
[13:04] <Laurenceb> but its nicer to be able to use lower power
[13:05] <Laurenceb> less heat, smaller batteries, easier power supply, less risk of RFI
[13:05] <MikeMc> What kind of range would be anticipated with 500mW?
[13:05] <Laurenceb> similar to with 434 with that antenna
[13:05] <Laurenceb> maybe twice the range if you were lucky
[13:05] <MikeMc> So what's the benefit of even bothering then?
[13:06] <Laurenceb> its debatable
[13:06] <Laurenceb> but if we have a decent ant then its certainly worth it if you need high data rate
[13:07] <RocketBoy> well here are the numbers - free space pathloss is 6db worse on 868 than 434
[13:07] <RocketBoy> but antennas are smaller
[13:07] <RocketBoy> for the same gain
[13:07] <SpeedEvil> 6dB for what distance?
[13:07] <RocketBoy> any
[13:07] <SpeedEvil> that sounds unlikely.
[13:07] <RocketBoy> beleive me
[13:08] <RocketBoy> go do the sums
[13:08] <Laurenceb> yeah thats right
[13:08] <SpeedEvil> If I have a 10cm gap - it's not going to attenuate a 868 signal over 4 times a 434
[13:08] <Laurenceb> but theres more background noise at 868?
[13:08] <SpeedEvil> Or am I confused again.
[13:08] <RocketBoy> there is a difference between near filed and far field
[13:08] <SpeedEvil> And quantisation noise
[13:09] <SpeedEvil> RocketBoy: sure.
[13:09] <RocketBoy> so don't think about 10cm
[13:10] <RocketBoy> like I say belive me and look it up
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[13:10] <SpeedEvil> RocketBoy: I have a 1KW transmitter 10m away. Surely I get ~0.8W/m^2 (assuming omnidirectional ant.
[13:10] <SpeedEvil> If I get ~0.2W/m^2 - why?
[13:10] <RocketBoy> is your antenna size the same?
[13:11] <SpeedEvil> Oh - right - I was assuming dishes on both ends.
[13:11] <RocketBoy> right - nd you will find the same size dish on 868 has 6db of gain over the same one used at 434
[13:12] <SpeedEvil> Ok - it's a definition thing then.
[13:12] <RocketBoy> so like I was going to say - you can compensate for the increased path loss with antenna gain
[13:12] <SpeedEvil> As it's not really path loss - but it's loss due to teh antenna capturing a smaller area of signal
[13:12] <RocketBoy> (but it becomes more directional)
[13:12] <SpeedEvil> the w/m^2 stays the same.
[13:13] <RocketBoy> thats a way of looking at it
[13:13] <SpeedEvil> But if you use a similar design of antenna, and scale it, the capture area drops as the freq rises.
[13:13] <RocketBoy> correct
[13:13] <RocketBoy> but the radiation pattern remains the same
[13:14] <SpeedEvil> yeah.
[13:14] <RocketBoy> (if you scale it)
[13:16] <RocketBoy> Anyway - 868MHz allows 500mW of output power - i.e. 17db up on 10mW of 434MHz
[13:17] <SpeedEvil> Also - old sat dishes are cheap.
[13:17] <RocketBoy> on the downside there is 6db more free space path loss
[13:17] <SpeedEvil> ~1.2m dish gives a nice amount of gain.
[13:17] <RocketBoy> dishes on 868 would be a bit unweildy
[13:17] <SpeedEvil> And isn't too unwieldy.
[13:17] <SpeedEvil> (if not mobile)
[13:19] <RocketBoy> a similar length yagi gives 3db back
[13:19] <RocketBoy> 868MHz is worse for drift than 434 (ppm crystal)
[13:20] <SpeedEvil> You can get remarkably inexpensive accurate crystals.
[13:20] <SpeedEvil> Used in phones.
[13:20] <SpeedEvil> Though you will need a PLL and stuff
[13:20] <RocketBoy> not with off the shelf modules
[13:20] <SpeedEvil> yeah
[13:20] <SpeedEvil> oh
[13:20] <SpeedEvil> it's type approved isnt' it
[13:20] <SpeedEvil> meh
[13:23] <RocketBoy> so I'm going to test a AFSK 868MHz setup shortly - AX.25 packet radio
[13:23] <SpeedEvil> Fun.
[13:24] <Laurenceb> nice
[13:24] <Laurenceb> how is it setup?
[13:24] <RocketBoy> I think the range will be at least 150Km based on the Nova1 flight
[13:25] <RocketBoy> then I'm going to try 9600baud packet
[13:25] <RocketBoy> the setup is more or less identical to Nova1
[13:25] <Laurenceb> need to finish my rtty code
[13:27] <RocketBoy> do you think it will be better than fldigi etc?
[13:29] <Laurenceb> certainly
[13:29] <Laurenceb> search for the callsign then initialise a DLL/FLL to decode the signal
[13:30] <Laurenceb> at some later date hopefully FEC and so on can be added
[13:33] <RocketBoy> FLL?
[13:33] <Laurenceb> frequency locked loop
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[15:33] Nick change: RocketBoy -> RocketBoy|Away
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[16:35] <Laurenceb> RocketBoy|Away: ping?
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[16:41] <RocketBoy|Away> Laurenceb: yep
[16:41] Nick change: RocketBoy|Away -> Rocketboy
[16:41] <Laurenceb> hi
[16:41] <Laurenceb> have you ever used the cesaroni classic propellant motors?
[16:41] <Rocketboy> yep
[16:42] <Laurenceb> how much smoke does it produce?
[16:43] <Rocketboy> a bit - its nowhere near as bad as the smokey type of propellant - but certainly worse than blue-thunder
[16:44] <Rocketboy> (blue streak? i cant remeber)
[16:44] <Laurenceb> interesting
[16:45] <Rocketboy> (yeah blue streak)
[16:45] <Laurenceb> theres different formulations of AP propellant
[16:45] <Rocketboy> yes
[16:45] <Laurenceb> the more smokey ones have greater Al content and a little more ISP
[16:45] <Laurenceb> some with very low Al are almost smokeless
[16:45] <Laurenceb> I was trying to work out what they use
[16:47] <Rocketboy> drop them a line (tell them what you are doing) - they won't tell you exactly what they use - but they might give you an indication
[16:47] <Laurenceb> yeah
[16:48] <Rocketboy> I'm sure they would be very interested in helping you use their products
[16:48] <Laurenceb> it doesnt make a huge difference to performance
[16:48] <Laurenceb> <1 second
[16:48] <Laurenceb> on the ISP. It looks like you can get 265seconds
[16:49] <Rocketboy> they certainly make quite a difference when you see them fly
[16:49] <Laurenceb> I mean the amount of aluminium
[16:50] <Laurenceb> you can test it with the USAF lab ISP code
[16:52] <Rocketboy> I wouln't get too hung up on squeezing the maximum out of everything to start with - optimize it when you have got it going
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[16:55] <Laurenceb> its not like I'm going to get anything built anytime soon
[16:55] <Laurenceb> CUSF could do something interesting with that level of performance
[16:56] <Laurenceb> you need a proper bell nozzle with a large expansion ratio of 35 or so
[16:58] <Laurenceb> I was thinking silica fabric ribbon wound on a mandrel, but if you wanted quick and easy you could use tufnol rod and a lathe
[17:00] <Rocketboy> Sorry - I haven't really been following the discussion on this here - are you talking about making space (100miles) - or orbit?
[17:00] <SpeedEvil> space is 'easy'
[17:00] <SpeedEvil> A moderate single stage solid on a balloon
[17:00] <Rocketboy> SSO from a balloon?
[17:01] <SpeedEvil> No - not orbit - space
[17:01] <SpeedEvil> orbit - even from a balloon is tricky
[17:01] <SpeedEvil> 100 miles isn't very tricky
[17:01] <Laurenceb> I was actually thinking of 200Km orbit
[17:01] <Rocketboy> your not kidding
[17:01] <Laurenceb> using two stage
[17:01] <SpeedEvil> point rocket vaguely up, shoot through balloon, you're more or less done
[17:01] <Laurenceb> but the basic design was for >100Km
[17:01] <jcoxon> afternoon all
[17:02] <Laurenceb> if you get that working you can add a second stage
[17:02] <Rocketboy> yo jcoxon
[17:02] <Laurenceb> its not that bad getting 200km orbit
[17:02] <jcoxon> hmmm hot glue + surgical spirit over2 days - good result
[17:02] <Laurenceb> but a lot harder than martlet
[17:03] <Laurenceb> jcoxon: hmm I'm not convinced it will hold up to temperature changes
[17:03] <Rocketboy> a flight test is called for
[17:03] <jcoxon> indeed it is
[17:03] <Laurenceb> RocketBoy: basically the design was for a two spin stabilised 1.8Kg GLOW rocket launched from 32Km
[17:04] <Laurenceb> *two stage
[17:04] <Laurenceb> putting 10grams into 200km orbit
[17:05] <Laurenceb> RocketBoy: off the shelf CF tube with cesaroni reloads
[17:05] <Rocketboy> well it certainly is a worthwile objective
[17:05] <jcoxon> Rocketboy, i'm working as quick as i can to get a payload in hte air :-p
[17:05] <jcoxon> just its a lot more work then most payloads hehe
[17:06] <Rocketboy> jcoxon: np
[17:06] <Laurenceb> I havent really done any more work on it, but I got as far as 4D sim code
[17:07] <jcoxon> grrr rapid don't stock DS1820 temp sensors
[17:09] <Rocketboy> yeah - they are particularly void of sensors
[17:09] <Rocketboy> i got mine from rs
[17:09] <jcoxon> yeah just transfering my shopping list to rs
[17:10] <Rocketboy> farnell do them too I think
[17:10] <jcoxon> i dislike ordering from farnell
[17:10] <Rocketboy> why?
[17:10] <jcoxon> its always a challenge and their website is rubbish
[17:10] <Laurenceb> Farnell is the place for ICs
[17:10] <Rocketboy> oh - I prefer it to RS
[17:10] <naxxfish> their website it rubbish, but they do stock a lot of ICs
[17:11] <naxxfish> and charge £way_too_much for basic connectors
[17:11] <Laurenceb> RS has stupid prices for engineering supplies
[17:11] <Laurenceb> naxxfish: toby.co.uk
[17:11] <Rocketboy> rs used to have an excellent site - but now its pants
[17:11] <Laurenceb> for connectors
[17:11] <jcoxon> suggestions for what photodiode to get?
[17:11] <naxxfish> Laurenceb: cool! thanks
[17:11] <jcoxon> yeah toby is the best for connectors
[17:12] <naxxfish> ha, they're down the road from where my mate works
[17:12] <Rocketboy> you want one matched to the LED wavelength
[17:12] <Laurenceb> RocketBoy: would you need a manufacturing license to put a cesaroni reload on a lathe?
[17:13] <jcoxon> http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=6655331
[17:13] <jcoxon> ?
[17:13] <Rocketboy> nope - not to put it on the lathe - but if you were wanting to turn it
[17:13] <Rocketboy> ;-)
[17:13] <jcoxon> rated down to -40
[17:13] <Laurenceb> to trim the ends to hemispheres
[17:14] Action: Rocketboy has visions of laurenceb wanting to turn plutonium hemispheres on a lathe
[17:14] <Laurenceb> heh
[17:14] <Laurenceb> are you trying to say its stupidly dangerous?
[17:15] <jcoxon> Rocketboy, don't give him ideas!
[17:15] <Laurenceb> jcoxon: hemispheres are old school
[17:15] <Laurenceb> you want an egg shaped primary
[17:15] <Rocketboy> I imagine turning propellant is an act of manufacture
[17:16] <Laurenceb> yeah thats what I was wondering
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[17:16] <Laurenceb> would have to get someone in the states to do it
[17:16] <Rocketboy> if you want to put hemispherical ends on the combustion chanber then make packing pieces
[17:16] <Laurenceb> or cesaroni themselves :p
[17:17] <Laurenceb> RocketBoy: they are heavy
[17:17] <Laurenceb> for the second stage it works better to turn the propellant
[17:17] <Laurenceb> but yeah packing pieces just work if you use al honeycomb
[17:18] <Laurenceb> avoiding them would give a bit of extra performance
[17:18] <Laurenceb> anyway you have to cut a reload down to get the right propellant mass for the second stage
[17:20] <Laurenceb> jcoxon: are you using a photodiode for the level sensor?
[17:20] <jcoxon> Laurenceb, yes
[17:21] <Laurenceb> jcoxon: have any op amps?
[17:21] <jcoxon> yes
[17:21] <Laurenceb> probably the best way to interface it
[17:21] <jcoxon> Rocketboy sent me 4 about 2 years ago
[17:22] <jcoxon> been sitting in my box of bits
[17:22] <Laurenceb> heh you cheapskate
[17:22] <jcoxon> my box of bits is amazing
[17:22] <jcoxon> i pretty much always order one more of things then i need
[17:22] <Laurenceb> the problem is the currents are quite small
[17:23] <Laurenceb> you can stick a low pass filter in there to reduce the noise
[17:23] <Laurenceb> but you want to turn the led on/off to remove stray light
[17:23] <Laurenceb> so maybe a few hundered Hz corner frequency or something
[17:24] <jcoxon> my ballast tank is black plastic
[17:24] <Rocketboy> that photodiode looks OK - a Red LED would be best
[17:25] <jcoxon> okay
[17:25] <Laurenceb> which photodiode are you using?
[17:25] <jcoxon> the one i linked to earlier
[17:26] Action: Laurenceb scrolls
[17:26] <jcoxon> grrr stupid rs - only selling LD1117V33 in packs of 50
[17:27] <jcoxon> guess a LF33CV will do
[17:27] <Laurenceb> jcoxon steady on there
[17:27] <Laurenceb> thats some serious photodiodery
[17:28] <Laurenceb> and long wavelenght operation but I'd be tempted to get something with a filter built in
[17:28] <Rocketboy> yeah its a bit overkill speed wise
[17:29] <Laurenceb> huge overkill
[17:30] <jcoxon> okay back to selecting
[17:31] <Laurenceb> http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=0195760
[17:32] <jcoxon> infrared?
[17:32] <Laurenceb> http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=6547921
[17:32] <Laurenceb> thats better
[17:32] <Laurenceb> yes
[17:32] <jcoxon> with an infrared led?
[17:32] <Laurenceb> yes
[17:33] <Laurenceb> to match the wavelenght of operation
[17:33] <jcoxon> and the silicon won't mind hte risk of getting wet?
[17:33] <Laurenceb> nope
[17:34] <jcoxon> good good
[17:34] <Laurenceb> but you dont want anything ionic on the pins
[17:34] <Laurenceb> as it will interfere
[17:34] <Laurenceb> best to have it at the top and the led at the bottom
[17:35] <jcoxon> yeah that was the current setup
[17:36] <Rocketboy> is the "Quantum yield" the senitivity of the photodiode? - ie the light to current transfer characteristic
[17:36] <Rocketboy> ?
[17:36] <Laurenceb> photon to electron
[17:37] <Laurenceb> % of absorbed photons promoting an electron across the depletion zone
[17:38] <Laurenceb> http://www.rlocman.ru/i/Image/2007/10/25/1.gif
[17:38] <Rocketboy> and therefore the transfer charactrisic - seems to suggest its linear
[17:38] <SpeedEvil> It is - fundamentally
[17:38] <Laurenceb> you want to stick a cap across that resistor
[17:38] <SpeedEvil> if you hold the voltage across a photodiode at zero, it's quite linear
[17:38] <SpeedEvil> If you don't, it's not really so much.
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[17:44] <rjharrison> Evening all
[17:46] <jcoxon> hmmm okay i think i'm ready to order
[17:46] <jcoxon> wow this has been a hassle
[17:46] <rjharrison> jcoxon what are you getting
[17:46] <jcoxon> just parts for ballasthalo3
[17:47] <jcoxon> such as more temp sensors and some photodiodes
[17:47] <jcoxon> crap forgot mosfet
[17:48] <MikeMc> evening
[17:48] <Laurenceb> heh write a list
[17:48] <jcoxon> recommended low power mosfets?
[17:48] <jcoxon> i'm using 3.3v
[17:48] <Laurenceb> thats good
[17:48] <Laurenceb> what opamp do you have
[17:49] <jcoxon> LM324N
[17:52] <rjharrison> What do opamps do
[17:52] <rjharrison> I often seen them mentioned
[17:52] <Laurenceb> sigh
[17:52] <rjharrison> ICARUS III does not have one
[17:52] <Laurenceb> see when I was starting electronics opamps were the first sting you touched
[17:52] <rjharrison> I'm just starting
[17:52] <Laurenceb> well after transistors :P
[17:52] <rjharrison> :)
[17:52] <Laurenceb> freaking ardunios are to blame
[17:52] <jcoxon> been nice
[17:53] <jcoxon> be*
[17:53] Action: Laurenceb starts going crazy
[17:53] <rjharrison> I'm still doing transistors
[17:53] <Laurenceb> I'm joking
[17:53] <Laurenceb> op amps amplify the difference between their two inputs
[17:53] <Laurenceb> they have very high gain such that they are unstable
[17:54] <Laurenceb> you stabilise them using external circuitry, and that forms the device you want
[17:55] <Laurenceb> e.g. add, subtract, integrate differentiate analogue signals, or amplify and filter frequency wise
[17:55] <Laurenceb> pretty much anything analogue can be done
[17:55] <jcoxon> on a mosfet is the gate source voltage the trigger?
[17:55] <Laurenceb> anyway, LM324N is hardly brilliant, but I think its just good enough for this purpose
[17:56] <Laurenceb> you will need to turn the led on/off to calibrate out both stray light and bias currents
[17:56] <Laurenceb> jcoxon: yes
[17:56] <rjharrison> Laurenceb thanks for that
[17:56] <jcoxon> Laurenceb, then subract ledOFF from ledON
[17:56] <Laurenceb> yes
[17:56] <naxxfish> the first thing i did when i started my course was opamps
[17:56] <rjharrison> I will wiki some more info
[17:57] <Laurenceb> naxxfish: opamps are cool
[17:57] <jcoxon> rjharrison, pah just use an arduino - they solve all problems
[17:57] <jcoxon> haha just kidding Laurenceb
[17:57] <Rocketboy> the saving grace of the LM324 is that its amazingly cheap - I got a tube of them for £1
[17:57] <naxxfish> i try to stay away from analogue stuff as much as possible :p
[17:57] <Laurenceb> RocketBoy: neat
[17:58] <Laurenceb> its better than 741
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[17:58] <jcoxon> Rocketboy, i guess thats why you sent them to me, never really worked out why :-)
[17:58] <Rocketboy> that and they will run from a single 5V supply and are close to rail to rail
[17:59] <Rocketboy> yeah - I was trying to use the tube up ;-)
[17:59] <Rocketboy> still got about 20
[17:59] <naxxfish> 741's are useless really
[17:59] <naxxfish> unless you happen to have negetive rails on your project
[17:59] <Laurenceb> I guess most of you are very familiar with IRC, but heres an introduction http://www.youtube.com/watch?v=O2rGTXHvPCQ
[17:59] <Laurenceb> naxxfish: rail splitter
[17:59] <Rocketboy> 741 - also about 30 years old
[18:01] <naxxfish> and are omnipresent in any course that involves learning opamps :p
[18:01] <Laurenceb> they arent that bad
[18:02] <naxxfish> given the choice, i wouldn't use them :p
[18:02] <jcoxon> Laurenceb, hehe IRC hackers
[18:08] <jcoxon> Laurenceb, is it worth me getting another type of opamp - i'm ordering things right now anyway
[18:09] <Laurenceb> maybe
[18:09] <Laurenceb> is there a parametric product search?
[18:09] <Laurenceb> looks for cheap, dip8, low offset voltage, low bias current, 3.3v single supply and rail to rail
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[18:15] <Rocketboy> ti do some nice op-amps
[18:16] <jcoxon> http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=3568830
[18:16] <jcoxon> ?
[18:17] <Laurenceb> think I've used that before
[18:17] Action: Laurenceb checks the datasheet
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[18:18] <Rocketboy> the LM324s work down to 3V
[18:18] <Laurenceb> thats a very nice opamp
[18:19] <Laurenceb> may as well buy one or two for that price
[18:19] <jcoxon> ooo its out of stock
[18:20] <jcoxon> http://uk.rs-online.com/web/search/searchBrowseAction.html?method=retrieveTfg&Ne=4294958891&Ntt=opamp&Nr=AND%28avl%3auk%2csearchDiscon_uk%3aN%29&Ntk=I18NAll&Ntx=mode%2bmatchallpartial&N=4294955182+4294912089&Ns=stockPolicy_uk|1||new_uk|1&Nty=1&binCount=113&multiselectParam=4294955182&selectAttribute=DIP8#breadCrumb
[18:22] <Laurenceb> or something similar, that was a bit of an overkill
[18:23] <SpeedEvil> Rocketboy: It really doesn't work at 3V
[18:23] <jcoxon> Laurenceb, http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=6674506
[18:23] <SpeedEvil> In that the majority of the input range is unavailable
[18:24] <jcoxon> oh thats out of stock too
[18:24] <Laurenceb> doh
[18:24] <Laurenceb> they dont keep stock levels very well
[18:25] <jcoxon> okay final one
[18:25] <jcoxon> http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=6674534
[18:26] <Laurenceb> thats easily good enough
[18:26] <Laurenceb> should be able to lower the led current an make it nice and low power
[18:26] <Laurenceb> have you got an led and photodiode?
[18:27] <jcoxon> got leds
[18:27] <jcoxon> and am getting the photodiode in the same order
[18:27] <Laurenceb> IR leds?
[18:29] <jcoxon> yup
[18:29] <jcoxon> have a mixed pack
[18:29] <Laurenceb> neat
[18:30] <Laurenceb> leds are quite narrow
[18:31] <Laurenceb> - wavelenght wise
[18:31] <Laurenceb> you want a IR photodiode with a narrow filter then an led to match
[18:31] <Laurenceb> that way you filter out ambient light
[18:32] <jcoxon> okay order done
[18:32] <jcoxon> finally!
[18:32] <jcoxon> now to wait...
[18:32] <jcoxon> and write some code to recognise float...
[18:33] <Laurenceb> whats the plan with the 500ml of ballast?
[18:34] <jcoxon> tis a tough one to work out
[18:34] <jcoxon> i think i'm going to get float, wait 30mins then dump some
[18:34] <jcoxon> to test that the system actually works
[18:34] <Laurenceb> how do you "get float" ?
[18:34] <jcoxon> with a pinhole floater
[18:34] <Laurenceb> ah ok
[18:34] <jcoxon> so that'll cause it to rise, i guess
[18:35] <Laurenceb> so you could float for a while by dropping ballast
[18:35] <jcoxon> this is where it gets hard
[18:35] <jcoxon> so ballasthalo2 floated without ballast
[18:36] <Laurenceb> yeah as you get to thinner air the hole becomes less significant
[18:36] <jcoxon> so one scenario would be to redo ballasthalo2 and then just test the ballast tanks at high altitude
[18:36] <Laurenceb> to the point you pretty much reach stable float
[18:36] <Laurenceb> brb
[18:36] <jcoxon> or we could actually use the ballast tanks to extend flight
[18:37] <jcoxon> make a bigger hole so we actually start descending, dump ballast to reestablish float
[18:38] <SpeedEvil> I'm unsure the pinhole actually mattered in the case of halo2.
[18:38] <jcoxon> SpeedEvil, i think it only mattered at sunrise
[18:38] <SpeedEvil> I think all that happened is it floated due to a mild superpressure in the balloon
[18:38] <jcoxon> when it wasn't big enough to dump enough helium to cope with the temp rise
[18:38] <SpeedEvil> hmm, yes, true
[18:39] <jcoxon> i think the key is that we test the ballast tank at high altitude
[18:39] <SpeedEvil> I mean - without a pinhole, the trajectory would have been the same
[18:39] <SpeedEvil> Maybe a hair higher.
[18:39] <jcoxon> so we 'achieve' float, wait 30mins then dump a known volume
[18:39] <jcoxon> perhaps let it settle down
[18:39] <jcoxon> then dump a bit more
[18:39] <SpeedEvil> I did the sums ages ago based on 1mB of helium expanding all the way, and the total volume exhausted wasn't large
[18:40] <jcoxon> dump by float time rather then any thing fancy
[18:40] <SpeedEvil> Is this with a controllable dump valve oir itnternal?
[18:41] <jcoxon> not sure what you mean
[18:42] <SpeedEvil> I mean are you going to remote control the dump.
[18:42] <SpeedEvil> Or is it onboard controlled.
[18:42] <jcoxon> oh onboard - preprogrammed
[18:43] <jcoxon> i was thinking of having 2 known ballast dumps of say 100mls each time to make sure the system gets tested then perhaps the rest controlled on some sort of logic
[18:43] <SpeedEvil> Something like on the GPS hour, or at altitude thresholds?
[18:44] <SpeedEvil> So you can tell even if comms has broken?
[18:44] <SpeedEvil> oh
[18:44] Action: SpeedEvil suffered a logic failure.
[18:44] <jcoxon> well we have 2 comms so its still sensible
[18:45] <SpeedEvil> 433 and 868?
[18:45] <jcoxon> rtty on 434.075 and morse on 434.225
[18:45] <SpeedEvil> ah
[18:45] <jcoxon> some data will be replicated on the morse though it is mainly a beacon
[18:55] <jcoxon> bbl
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[19:11] <Laurenceb> I think the point about pinholes is they dont scale as the envelope expands
[19:11] <Laurenceb> so they become dramatically less effective with altitude
[19:12] <SpeedEvil> I don't think it's quite going to be inversely proportional to air density - assuming constant pressure - but it'll be close
[19:14] <Laurenceb> pressure difference decreases as the envelope expands, but the decreasing density increases the flow
[19:14] <Laurenceb> its complex
[19:14] <SpeedEvil> increases the jet velocity yeah
[19:16] <Laurenceb> http://en.wikipedia.org/wiki/Orifice_plate#Flow_of_gases_through_an_orifice
[19:17] <Laurenceb> equation 3 is the business
[19:17] <Laurenceb> m_dot corresponds to the loss of bouyancy
[19:18] <Laurenceb> and density and delat pressure decrease with altitude
[19:18] <Laurenceb> so the rate of loss decreases
[19:19] <SpeedEvil> Up to a limit - I suspect delta pressure may not decrease with altitude as the elastic limit is approached
[19:21] <Laurenceb> yes
[19:21] <Laurenceb> you could actually use that effect to level off a latex balloon as it approaches burst altitude
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[19:29] <SpeedEvil> hopefully rjharrison's launch will provide nice hard numbers.
[19:31] <natrium42> twss; any idea when the launch is?
[19:34] <Laurenceb> does he have an envelope pressure sensor?
[19:38] <Laurenceb> I'm still looking for a good enough pressure sensor for a pitot tube
[19:43] <SpeedEvil> yes
[19:43] <SpeedEvil> Dunno what it is
[19:44] <Laurenceb> I cant find anything stable enough to be useful in a low speed UAV
[19:48] <Laurenceb> need errors in the region of 1Pa
[19:50] <Laurenceb> http://tinyurl.com/ydzkaew
[19:51] <Laurenceb> expensive as well
[19:52] <SpeedEvil> thermal?
[19:52] <SpeedEvil> Crack a bilb, hot-wire
[19:52] <SpeedEvil> bulb
[19:52] <Laurenceb> yeah
[19:53] <Laurenceb> should be able to get accurate airspeed with no other sensors in fact
[19:54] <Laurenceb> you know temperature and density to within a few %
[19:55] <Laurenceb> http://www.sensortechnics.com/index.php?fid=300&fpar=YToxOntzOjQ6InBjaWQiO3M6MjoiOTkiO30%3D&isSSL=0&aps=0&blub=c586664226675348eeddf65c82c14fe2
[19:56] <SpeedEvil> Expensive
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[19:58] <Laurenceb> and too unstable
[19:59] <SpeedEvil> http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=CM7219-ND
[19:59] <SpeedEvil> hot wire anemometers can actually work very well
[19:59] <Laurenceb> page 3 of datasheet
[19:59] <SpeedEvil> pitot tube, orifice, ...
[20:02] <Laurenceb> that sensor has an offset of +-6Pa with +-1G of accel
[20:02] <Laurenceb> thats not nice
[20:02] <Laurenceb> 4Pa warm up offset and 2Pa over temperature range, 4Pa with 1 year aging
[20:03] <Laurenceb> I could probably live with everything apart from the warm up and accel dependant offsets
[20:03] <Laurenceb> its a few times more than is managable for a low speed UAV
[20:04] <Laurenceb> diydrones use a dodgy control loop technique where the pitot tube is only controlling things over short timescales
[20:05] <Laurenceb> I wanted actualy airspeed as its useful for lots of more advanced navigation techniques/wind/turbulence modelling
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[20:09] <SpeedEvil> ultrasound?
[20:10] <Laurenceb> http://www.aoe.vt.edu/aoe4154/hotwirelab.pdf
[20:10] <Laurenceb> that looks good
[20:10] <Laurenceb> there was that french flapper design
[20:10] <Laurenceb> but thats rather impractical unless you have a wind tunnel ect
[20:11] <Laurenceb> hot wire looks good, have to get down the current draw and make it durable - maybe someone sells the sensors
[20:11] <Laurenceb> there was a team working on kapton film based sensors at oxford
[20:12] <Laurenceb> http://cgi.ebay.co.uk/Hot-Wire-Anemometer-Tecpel-AVM-714_W0QQitemZ350241098607QQcmdZViewItemQQptZUK_BOI_Electrical_Test_Measurement_Equipment_ET?hash=item518bff0b6f
[20:12] <Laurenceb> ouch
[20:12] <Laurenceb> m/s Range: 0.2 ~20.0 m/s with 0.1m/s resolution , +/-(5% +1 d) reading
[20:12] <Laurenceb> thats right in the middle of UAV terratory
[20:16] <SpeedEvil> ouch?
[20:17] <Laurenceb> the price
[20:18] <SpeedEvil> Crack open a bulb, run it at 1/5th nominal voltage or so - worked well
[20:19] <Laurenceb> will it oxidise?
[20:20] <SpeedEvil> not IME - at low temps
[20:20] <SpeedEvil> ~200C
[20:20] <Laurenceb> hmm then the air temperature becomes more important
[20:21] <Laurenceb> guess you know air temperature to 20C or less so thats just 10%
[20:22] <Laurenceb> those bulbs use tungsten I guess?
[20:22] <SpeedEvil> y
[20:31] <Laurenceb> If a light bulb envelope leaks, the hot tungsten filament reacts with air, yielding an aerosol of brown tungsten nitride, brown tungsten dioxide, violet-blue tungsten pentoxide, and yellow tungsten trioxide which then deposits on the nearby surfaces or the bulb interior.
[20:32] <Laurenceb> thats going to take high temperatures
[20:36] <Laurenceb> http://www.google.co.uk/url?sa=t&source=web&ct=res&cd=2&ved=0CBYQFjAB&url=http%3A%2F%2Fwww.fusion.ucla.edu%2Fapex%2Fmeeting5%2F1ghoniem1198.pdf&ei=gcL9SqGyLNWd4Qab8_mDDA&usg=AFQjCNE7xNgV0G_rvoWmdciar6WDsSl1bA
[20:39] <Laurenceb> looks like you could get up to 900C with tungsten
[20:39] <Laurenceb> thats nice and hot
[20:39] <Laurenceb> needs a driver circuit that doesnt waste half the power in a resistor
[20:41] <Laurenceb> http://www.efunda.com/designstandards/sensors/hot_wires/hot_wires_theory.cfm
[20:42] <Laurenceb> constant temperature looks nice
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[21:01] <Rocketboy> actually that is quite cool - very simple and you can see how it would be effective
[21:01] Nick change: Rocketboy -> RocketBoy|Away
[21:01] <RocketBoy|Away> bbl
[21:04] <Laurenceb> cya all
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[22:20] <MikeMc> Looks like we are in for a battering tonight
[22:26] Action: SpeedEvil loce
[22:27] Action: SpeedEvil loves yr.no
[22:27] <SpeedEvil> http://www.yr.no/place/United_Kingdom/Scotland/Glenrothes/hour_by_hour.html
[22:27] <SpeedEvil> 7mm or so in the next 2 hours.
[22:27] <SpeedEvil> 4 miles away - 14mm in 2 hours
[22:31] <MikeMc> eek
[22:31] <MikeMc> Looks like i'll get heavy winds - http://www.yr.no/place/United_Kingdom/England/Orpington/hour_by_hour.html
[22:35] <SpeedEvil> Why can't the met office do that/
[22:35] <SpeedEvil> Stupid 'must make money'
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[22:43] <MikeMc> yeah
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[00:00] --- Sat Nov 14 2009