highaltitude.log.20080327

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[00:40] <rocketboyV1> down - phew
[00:40] <rocketboyV1> night
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[11:36] <jcoxon> morning edmoore
[11:36] <edmoore> hi jcoxon
[11:36] <edmoore> how's it going?
[11:36] <jcoxon> okay,
[11:36] <jcoxon> just found out that cocoamodem only decodes baudot and not ascii
[11:37] <edmoore> yes
[11:37] <edmoore> well rtty is baudot
[11:37] <jcoxon> yeah but steve sends it ascii
[11:37] <edmoore> oh righty
[11:37] <edmoore> time to send a grovelmail :)
[11:37] <jcoxon> i assume as its easier to link into serial ports etc
[11:38] <jcoxon> well i can get hold of the code for cocoamodem
[11:38] <jcoxon> so in theory i could add the feature in
[11:38] <jcoxon> or i could persuade rocketboy to change his transmission to baudot :-p
[11:40] <edmoore> http://news.bbc.co.uk/1/hi/technology/7314362.stm
[11:40] <edmoore> still, not really applicable to us
[11:40] <jcoxon> yeah i saw
[11:41] <jcoxon> well we could fly close to an aeroplane and get reception :-p
[11:41] <edmoore> I wonder what the caa would say
[11:41] <jcoxon> there might be a little upset
[11:41] <edmoore> if we fired sucking harpoons onto passing planes
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[11:41] <jcoxon> haha
[11:41] <edmoore> that could let us do transatlantic the other way!!!
[11:41] <jcoxon> piggyback
[11:42] <jcoxon> oh edmoore, i'm setting up my cupboard server
[11:42] <jcoxon> would you like an account to play with?
[11:42] <edmoore> a what server?
[11:42] <edmoore> oh god yes!
[11:42] <jcoxon> its in my cupboard
[11:42] <edmoore> I would love some webspace proper
[11:42] <edmoore> lol
[11:42] <edmoore> what kinda deal can you offer me jimbob? :p
[11:43] <jcoxon> well its going to go through our home broadband so it'll be a dynamic dns thingy whatsit
[11:43] <jcoxon> also you'll get a nice linux shell account to play with
[11:43] <edmoore> do you have a decent upload speed?
[11:44] <jcoxon> hmmm only 448kbps
[11:44] <jcoxon> 6720kbps down though
[11:44] <edmoore> that's fine tho for browsing
[11:44] <jcoxon> oh and its unlimited download
[11:44] <edmoore> oooo
[11:45] <edmoore> well I'd love an account, yes
[11:45] <edmoore> thankyouverymuch
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[11:45] <jcoxon> okay cool, well i've set it up but am having some network issues - damn wireless cards - tempted to run a cable
[11:49] <edmoore> Am reading up on mars descents
[11:49] <edmoore> they have this really interesting problem when it comes to landing anything larger than what they've landed so far
[11:49] <edmoore> in as far as - there's too much atmosphere to do a sort of lunar style landing with rocket decelleration
[11:50] <edmoore> but not enough to do the current heat shield then parachute that they do now for small buggies
[11:50] <edmoore> it's a pretty big problem for landing 1tonne +
[11:50] <edmoore> they'd be look at 20 tonnes for manned stuff
[11:51] <mc-> ed, I just met your fearless admin person at Charterhouse
[11:51] <edmoore> oh blimey
[11:51] <edmoore> jen is organizer supreme
[11:52] <mc-> she doesn't know if you will coming to the conf
[11:52] <edmoore> me neither!
[11:53] <mc-> if Laurence is around, tell him, I've managed to route his PCB
[11:53] <mc-> I helped the autorouter, to be precise
[11:54] <edmoore> willdo
[11:54] <mc-> don't bother with manual routing, I'm converted to autorouters now
[11:55] <mc-> I also spoke to Will P from xprize
[11:56] <edmoore> oh?
[11:56] <edmoore> have you converted him/
[11:56] <mc-> nearly, he could see my logic
[11:57] <mc-> he suggested I go to the Strasbourg conf in May
[11:59] <mc-> but I don't think I have time
[11:59] <mc-> would your new employer pay for your expenses to attend?
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[12:04] Action: Laurenceb is running freerouting.net
[12:04] <mc-> just sent you an email
[12:04] <Laurenceb> ok
[12:04] <mc-> all done
[12:04] <Laurenceb> I've switched to XP and got it running
[12:05] <Laurenceb> wow cool
[12:05] <mc-> had to space out some of the components, then it routed fairly quick
[12:05] <Laurenceb> right
[12:06] <mc-> I'm impressed with the routing
[12:06] <Laurenceb> me too
[12:09] <Laurenceb> ok, I'm just looking at the .brd
[12:10] <Laurenceb> looks like it can be tweaked a bit, and I'd like to try adding a groundplane
[12:11] <mc-> autorouting is almost fun now
[12:12] <Laurenceb> hehe
[12:13] <Laurenceb> it might take a bit of tweaking to meet pcbcarts design rules
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[13:08] <jcoxon> test
[13:13] <Laurenceb> hello world
[13:13] <jcoxon> hello Laurenceb
[13:14] <Laurenceb> hello jcoxon
[13:14] <Laurenceb> what are you testing?
[13:15] <jcoxon> i'm planning on moving zeusbot to my home server i just set up, was testing that it was logging
[13:15] <Laurenceb> cool
[13:16] <jcoxon> i'm still working out the whole logistics and whether it is work it
[13:16] <jcoxon> worth*
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[13:52] <Laurenceb> hey edmoore
[13:52] <edmoore> hi
[13:52] Action: Laurenceb has a routed board
[13:52] <edmoore> ooooh
[13:52] <edmoore> nice
[13:52] <Laurenceb> thanx to some help from mc-
[13:52] <edmoore> pics?
[13:52] <Laurenceb> needs a little more work...
[13:52] <Laurenceb> mc- used freerouting on it
[13:52] <Laurenceb> its very impressive
[13:53] <Laurenceb> better than the eagle router by quite a bit
[13:53] <Laurenceb> but it needs a bit of hand optimising
[13:53] <Laurenceb> will probably end up around 35x45mm
[13:55] <edmoore> impressive
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[14:24] <Laurenceb> http://wiki.ukhas.org.uk/projects:ukhas_glider_project:flight_computer
[14:27] <Laurenceb> needs a bit more work to meet the drc
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[14:35] <Laurenceb> hey there mc-
[14:35] <mc-> how's it going?
[14:35] <Laurenceb> just working on fine tuning it - http://wiki.ukhas.org.uk/projects:ukhas_glider_project:flight_computer
[14:36] <mc-> looks good, and only slightly larger than your first layout
[14:36] <Laurenceb> yes, should end up 35x45 mm
[14:37] <mc-> imagine trying to route it manually..
[14:37] <Laurenceb> hehe
[14:37] <Laurenceb> thanx for all the help :P
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[14:38] <mc-> I wanted to understand autorouters, as I can't face manual routing
[14:39] <mc-> by the way, have a look at olimex.com for pcbs
[14:40] <Laurenceb> I'm thinking of pcbcart.com
[14:40] <Laurenceb> I've used batchpcb before, but they are slow and lost one delivery in the post
[14:41] <mc-> what did pcbcart.com quote? Olimex have a fixed price for a 100x160mm area
[14:41] <mc-> I think shipping charges from China are high?
[14:43] <Laurenceb> not really
[14:44] <Laurenceb> pcbcart have a tooling cost, which is annoying
[14:44] <Laurenceb> but they charge per area, and have a good election of materials
[14:44] <Laurenceb> selection*
[14:44] <Laurenceb> batchpcb just have FR4
[14:45] <mc-> olimex shipping is around $5 for standard delivery
[14:45] <Laurenceb> the per area cost is really cheap, a few $ for these
[14:45] <Laurenceb> but how much for one panel?
[14:46] <mc-> I think it's around $30 total
[14:46] <Laurenceb> right
[14:46] <Laurenceb> ok, I was under the impression it was more
[14:47] <Laurenceb> might try it, the problem is they can only do 10mil tracks
[14:47] <Laurenceb> batchpcb go down to 8, and pcbcart even smaller
[14:48] <Laurenceb> oh well, I'll try a drc with everythnig at 10mil
[14:49] <Laurenceb> oh god: 300 errors
[14:50] <mc-> it you can fit it into 33x50mm, then you can get 9 PCBs on a panel for $30
[14:50] Action: Laurenceb checks olimex
[14:50] <mc-> you'll need to re-route with larger spacing
[14:54] <Laurenceb> ok... olimex's rules are a bit complex... batchpcb automates it all
[14:54] <Laurenceb> I think I've entered it all ok, got 240 errors now
[14:56] <Laurenceb> lol, looks like there were rounding errors with my holes, as I was working in mm
[15:05] <edmoore> Laurenceb: you can have 8mil spacing
[15:05] <edmoore> just takes longer
[15:09] <Laurenceb> from the site it looks like 8mil
[15:09] <Laurenceb> for everything :/
[15:10] <Laurenceb> and their via clearances are crazy
[15:13] <Laurenceb> oh I see
[15:13] <Laurenceb> why bother :(
[15:14] Action: Laurenceb heads off to pcbcart
[15:20] <Laurenceb> pcbcart is £23 + postage
[15:20] <Laurenceb> for 8 days
[15:23] <Laurenceb> pcbs are a pain :(
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[15:48] <Laurenceb> well I'm down to 80 errors
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[16:02] <mc-> can you adjust the clearances in the autorouter?
[16:02] <mc-> then you don't have to manually reroute?
[16:02] <mc-> how many pcbs do you get from pcbcart for 23?
[16:10] <Laurenceb> just one
[16:10] <Laurenceb> but you could get more for about £6 each
[16:11] <Laurenceb> going down to less for 5+, 10+ ect
[16:13] <mc-> so olimex is good value, but a bit more difficult to meet their clearances etc
[16:17] <mc-> there's a clearance matrix in freerouter
[16:18] <mc-> but I can't work out the units
[16:19] <Laurenceb> I'm hand routing now
[16:20] <Laurenceb> down to 41 errors using olimex's specs
[16:20] <mc-> why not reroute with the autorouter?
[16:21] <Laurenceb> hmm
[16:22] <Laurenceb> I prefer to do it like this, hand routing can be better
[16:24] <edmoore> I think it almost always is in projects of this size and complexity
[16:24] <edmoore> (or lack thereof)
[16:25] <mc-> I've worked out the freerouter clearances, just trying rerouting, so I can use olimex on my pcbs in future.
[16:28] <Laurenceb> cool
[16:28] <Laurenceb> down to 25 errors :P
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[16:40] <Laurenceb> brb
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[16:54] <Laurenceb> done, no errors XD
[16:56] <Laurenceb> http://wiki.ukhas.org.uk/projects:ukhas_glider_project:flight_computer
[16:58] <Laurenceb> just needs a silkscreen now
[17:30] Action: natrium42 punches Laurenceb for not using 45 and 90 degree angles only
[17:31] <Laurenceb> hehe
[17:31] <Laurenceb> its more organic
[17:32] <Laurenceb> my components aren't at weird angles this time :P
[17:33] <natrium42> :P
[17:33] <Laurenceb> if I'd designed it completely by hand I'd have done that as well
[17:34] <Laurenceb> the pcb fabs can do any angle, so you might as well take advantage of that IMO
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[17:40] <natrium42> Laurenceb, this router looks pretty awesome --> http://www.reltronics.com.au/topor.php
[17:40] <natrium42> and is in line with your design practice :)
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[17:42] <Laurenceb> haha sweet
[17:42] <Laurenceb> love the animation
[17:42] <natrium42> :)
[17:42] <natrium42> i have to try this router sometime
[17:43] <natrium42> it's free for a certain number of layers, i believe
[17:45] <Laurenceb> yes, 8 layers, 125 nets
[17:45] <Laurenceb> it looks amazing
[17:46] <Laurenceb> I'd have to work out how to use it with eagle
[17:46] <natrium42> i think you can'd use it with eagle unfortunately
[17:46] <natrium42> i was planning to use it with protel
[17:46] <Laurenceb> ah you can import dsn
[17:46] <Laurenceb> ok, I have a brd to dsn convertor
[17:48] <natrium42> cool
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[17:51] <Hiena> Good evening!
[17:54] <Laurenceb> hmm "import error"
[17:58] <Laurenceb> it isnt able to import my dsn file :(
[18:00] <Laurenceb> so fustrating :(
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[18:02] <Laurenceb> natrium42: can you try?
[18:02] <Laurenceb> if you go to www.freerouting.net and get the ulp
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[18:07] <Laurenceb> natrium42: any luck? can you try it?
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[18:20] <Laurenceb> anyone want to try this for me?
[18:20] <Laurenceb> http://www.reltronics.com.au/topor.php
[18:22] <Laurenceb> together with the brd to dsn ulp file from freerouting.net
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[19:39] <Laurenceb> http://wiki.ukhas.org.uk/projects:ukhas_glider_project:flight_computer
[19:39] <Laurenceb> ^ board is finished :P
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[19:55] <akawaka> nice
[19:55] <akawaka> gonna go with a custom board next time
[19:55] <akawaka> this full linux box is unweildy and underused
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[20:16] <Laurenceb> pcbcart are giving me an insane tooling cost now :(
[20:18] <Laurenceb> looks like they aren't any good
[20:19] <natrium42> just use gold phoenix
[20:19] <natrium42> :P
[20:21] <Laurenceb> but you need a big panel
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[20:22] <Laurenceb> this is annoying
[20:22] <natrium42> guess so
[20:22] <natrium42> maybe somebody in here wants to make pcbs and you can combine?
[20:22] <Laurenceb> maybe :P
[20:23] <Laurenceb> I really want to avoid batchpcb, and olimex is rather poor
[20:24] <natrium42> yeah, goldphoenix is pretty damn fast
[20:24] <Laurenceb> maybe I should make a cnc machine for doing vias and things
[20:24] <natrium42> you can pay extra for rush service
[20:25] <Laurenceb> oh hang on... pcbcart likes nice sizes...
[20:27] <Laurenceb> or maybe not... this is just stupid
[20:27] Action: natrium42 likes good service and speed :P
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[20:31] <Laurenceb> damnit looks like I'll have to use batchpcb
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[20:44] <Laurenceb> arrgg I've forgotten how to use batchpcb
[20:45] <Laurenceb> any batchpcb users?
[20:53] <Laurenceb> nvm sorted it
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[21:42] <Laurenceb> I've sent the flight computer off to batchpcb
[21:42] <Laurenceb> it meets their drc
[21:43] <Laurenceb> I'll probably send off an order to batchpcb for a few boards, and also a fixed radio board
[21:44] <edmoore> cool
[21:44] <edmoore> should have them by July then
[21:44] <Laurenceb> if anyone wants some boards feel free to let me know and we can save a bit on post
[21:44] <Laurenceb> lol
[21:44] <Laurenceb> yes
[21:44] <Laurenceb> oh well I have exams
[21:44] <Laurenceb> it usually takes 3 weeks
[21:44] <Laurenceb> bbl
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[22:24] <edmoore> I need Laurence of Arabia
[22:30] <natrium42> lol?
[22:32] <edmoore> no seriously
[22:33] <edmoore> I have a huge lump of cheddar cheese, some biscuits, and half a bottle of red wine
[22:33] <edmoore> and I need a proper man film to consume it all with
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[22:45] <edmoore> hi RocketBoy_
[22:45] <edmoore> Just read your email
[22:45] <RocketBoy_> hey ed
[22:45] <edmoore> so what's your gut instinct on the direction to head in?
[22:46] <RocketBoy_> yeah its all a bit complex
[22:46] <RocketBoy_> instinct wise I guess HF packet radio
[22:46] <edmoore> I tried to write down some stuff but got the point that I couldn't tell if it was just complicated and irreducible or I'd made an algebraic error
[22:46] <RocketBoy_> there is a lot of support about
[22:47] <edmoore> what kind of number is HF?
[22:47] <Laurenceb> RocketBoy_: the radiometrix radio modules, they have a 100K pullup on the data input?
[22:47] <RocketBoy_> sorry - HF reffers to the HF bands - the type of packet radio used there
[22:47] <RocketBoy_> HF = High frequency
[22:48] <RocketBoy_> below 30MHz
[22:48] <edmoore> yep sure, but I mean what kind of numbers are they?
[22:48] <edmoore> oh ok
[22:48] <edmoore> cool
[22:48] <edmoore> how does that stand from a regulatory POV?
[22:49] <RocketBoy_> its just narrow band - used cos the HF bands are more crowded than VHF
[22:49] <RocketBoy_> so its the same reglatorty wise
[22:49] <edmoore> cool
[22:49] <RocketBoy_> as long as you stick using the licence exempt modules
[22:50] <edmoore> and i guess that means larger antennas?
[22:50] <RocketBoy_> yeah on the HF bands the wavelength is much longer
[22:51] <RocketBoy_> however the free space path loss is dependant on frequency - so on HF the dB loss between 2 points in space is less than VHF
[22:51] <edmoore> so purely practically, we'd need larger appendages on payloads
[22:51] <RocketBoy_> the lower the frequency the less the free space path loss
[22:52] <RocketBoy_> yeah -its a bit of a trade off - on HF you can get away with lower antenna gain
[22:53] <edmoore> ok cool
[22:53] <RocketBoy_> but on VHF the FSPL is more - but can be compensated by antennas with more gain (e.g. yagis)
[22:53] <edmoore> well I was looking at that sort of stuff on the kd7lmo site
[22:53] <edmoore> I like they way they use DDS but use the GPS PPs to help combat drift
[22:53] <edmoore> they claim to have had excellent results with it
[22:57] <RocketBoy_> yeah thats a way for sure - to use the Licence exempt modules in that way we would need to sniff the RF output phase lock it using the input control voltage
[22:57] <RocketBoy_> ... and phase lock it ...
[22:57] <edmoore> lol
[22:57] <edmoore> maybe for a rainier day
[22:58] <Laurenceb> the lassen iq has 1pps output
[22:58] <RocketBoy_> yeah - I think thats the key here - how much effort do we want to expend on developing a perfect radio system
[22:59] <edmoore> Laurenceb: yup
[22:59] <edmoore> and it's sitting there looking useful
[22:59] <edmoore> RocketBoy_: do you know how much it costs to get a DIY thing licensed?
[23:00] <Laurenceb> gtg, cya folks
[23:00] Laurenceb (n=Laurence@host81-157-248-24.range81-157.btcentralplus.com) left irc:
[23:00] <edmoore> I ask this quite seriously as if it's of benefit to lots of people then I might be able to get some CUSF money
[23:00] <RocketBoy_> I have no real idea - i imagine it needs submitting to an independent test house at least - so low Ks GPB
[23:02] <RocketBoy_> I'm not sure what the advantage is - if its going to be LE then its going to have the same power and modes as the existing modules.
[23:02] <edmoore> oh...
[23:02] <edmoore> ks was more than I had in mind :\
[23:03] <RocketBoy_> if its a licensed frequency its going to cost to license it.
[23:03] <RocketBoy_> I honestly don't think the 10mW 434MHz FM is a significant restriction - the NOVA flights showed it has the range
[23:04] <RocketBoy_> Putting an encoding scheme round the 434MHz LE modules is probably the better approach - extend the reliability that way
[23:05] <edmoore> sure
[23:06] <RocketBoy_> I mean the worst case distance is 600km - line of sight at 100k ft
[23:06] <edmoore> so what sort of encoding scheme do you reckon?
[23:08] <RocketBoy_> well I think thats the problem - we either go for an off the shelf decoder (like RTTY, packet or PSK31)
[23:09] <RocketBoy_> in which case we need to enulate the data they are expecting
[23:09] <RocketBoy_> or we build our own
[23:10] <RocketBoy_> in which case we need to do our own sound card software
[23:11] <RocketBoy_> the whole radio data thing is a complete trade off between complexity and performance
[23:11] <edmoore> yeah, shame that :)
[23:12] <RocketBoy_> getting good performance with low signal levels requies complex encoding/decoding shemes
[23:12] <RocketBoy_> so what we need is a balance - reasonable performance from not too complex
[23:14] <RocketBoy_> standard packet radio would be a good choice - however it has a CRC check that most decoders discard the packet if one bit is corrupted
[23:15] <edmoore> yeah, it's a same as for our low data rates just eyeballing it often seems sufficient
[23:16] <RocketBoy_> perhaps something like packet radio but with error correction - like Turbo codes or Reed-Solomon
[23:17] <RocketBoy_> Something like low shift FSK (or MFSK) with Turbo code or RS protected packets.
[23:18] <edmoore> and multiple devices can operate on a single freq?
[23:22] <RocketBoy_> Yeah - thats true of packet in general
[23:22] <RocketBoy_> (well of most schemes anyway)
[23:22] <edmoore> yeah, I guess that's quite exciting for the future
[23:22] <RocketBoy_> Its a bit like co-ax Ethernet
[23:23] <RocketBoy_> I guess - we should just decide what we want to do for Atlas
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[23:23] <edmoore> ok
[23:23] <edmoore> well james has the source to cocoa modem
[23:23] <edmoore> and thinks he can add ascii functionailty
[23:24] <edmoore> the author said it would be trivial, anyway
[23:24] <RocketBoy_> sounds OK
[23:26] <RocketBoy_> Can anyone help with ubuntu?
[23:26] <edmoore> equally, it's probably not too difficult to write something to decode a newer scheme as we have the source
[23:26] <edmoore> I used it for about a fortnight.... I mean, ask, but I probably can't :)
[23:27] <RocketBoy_> yeah - OK well see what jcoxon has to say
[23:28] <RocketBoy_> well my problem is file systems - the DOS file systems keep comming and going from ubuntu
[23:29] <edmoore> natrium42 might be able to help
[23:29] <RocketBoy_> it says it cant mount the file system when I try to navigate to them
[23:29] <RocketBoy_> actually it says - Unable to mount the volume
[23:30] <RocketBoy_> OK will I'll see if he can help
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[23:33] <jcoxon> hey all
[23:33] <RocketBoy_> just the chap - we were talking about you
[23:34] <RocketBoy_> are you happy enough with the coco code to convert it to ASCII
[23:35] <RocketBoy_> what speed and frequency shifts does it support?
[23:35] <jcoxon> indeed, just catching up with the logs
[23:35] <jcoxon> oh and i can help you with ubuntu
[23:35] <RocketBoy_> spiffing
[23:35] <jcoxon> right
[23:35] <jcoxon> so
[23:36] <jcoxon> i have the source - as ed has seen its an incredible program
[23:36] <jcoxon> i think i've identified where i need to make the changes but its going to take some work - and i need to read up on some theory
[23:37] <jcoxon> so lets not change the way we are doing things
[23:37] <RocketBoy_> sounds OK
[23:37] <jcoxon> keep rtty asci
[23:37] <jcoxon> i
[23:37] <jcoxon> as we can always decode it in windows
[23:37] <jcoxon> if i can't get it right
[23:37] <edmoore> yes exactly
[23:37] <jcoxon> new scheme for another day
[23:38] <edmoore> it'd be cool to try and get an uplink working with this new system too
[23:38] <RocketBoy_> yep that makes sense in the immediate future
[23:38] <RocketBoy_> well I have an uplink 3/4 built
[23:39] <jcoxon> for atlas we need simple tested kit
[23:39] <RocketBoy_> I don't think we can spare the extra weight for atlas
[23:39] <edmoore> no agreed
[23:39] <jcoxon> if atlas works we can always expand
[23:40] <RocketBoy_> but sure in the mid term
[23:40] <RocketBoy_> perhaps a flight just to test rad-io systems would be a good idea
[23:40] <RocketBoy_> range test and uplink
[23:41] <jcoxon> true, perhaps a single balloon
[23:41] <jcoxon> fill it up lots
[23:41] <RocketBoy_> yeah
[23:41] <edmoore> stormy day
[23:41] <RocketBoy_> and a good cutdown
[23:42] <jcoxon> yeah
[23:42] <jcoxon> okay
[23:42] <jcoxon> so lets continue as planned
[23:42] <RocketBoy_> yeah
[23:43] <RocketBoy_> OK so is edmoore doing the radio
[23:43] <jcoxon> is he?
[23:43] <RocketBoy_> (the transmitter end)
[23:43] <edmoore> am I?
[23:44] <RocketBoy_> I'm asking
[23:44] <edmoore> I thought we were using one of your rtty modules
[23:44] <RocketBoy_> oh
[23:44] <edmoore> as they work
[23:44] <RocketBoy_> Can do - NP
[23:44] <jcoxon> but doesn't it have to be i2dc
[23:44] <edmoore> no, we can bit-bash rs232
[23:44] <edmoore> he says.....
[23:45] <RocketBoy_> yeah better
[23:45] <jcoxon> fair enough
[23:46] <jcoxon> okay
[23:46] <edmoore> james - do you still have a cutdown?
[23:46] <jcoxon> a circuit?
[23:46] <edmoore> can we do soemthing that doesn't involve a massive cap?
[23:46] <jcoxon> yeah
[23:47] <edmoore> just a mosfet and hope all will be well
[23:47] <jcoxon> hmmmm, we need these cutdowns to work
[23:47] <edmoore> not necessarily
[23:47] <jcoxon> if we go for dual balloon
[23:47] <edmoore> well, we'd like to wait for burst
[23:48] <edmoore> on the big balloon
[23:48] <RocketBoy_> The main problem (without a cap) is that when the cutdown goes the current can drag the battery down
[23:48] <edmoore> yeah - but then we are using the good lithiums
[23:48] <edmoore> maybe soemthing to investigate
[23:49] <edmoore> it's just I'm sure those caps must be >10g
[23:49] <jcoxon> hmmmm
[23:49] <RocketBoy_> When the igniter flares the plasma generates almost a short circuit
[23:49] <edmoore> yes was thinking about that
[23:49] <RocketBoy_> - its not just the resistance of the igniter (which is 1.1 ohm)
[23:49] <edmoore> using a 0.1ohm resistor or something
[23:49] <edmoore> in series
[23:50] <RocketBoy_> yeah thats one approach - or a current limiting FET cct
[23:50] <RocketBoy_> 3A should be OK
[23:51] <RocketBoy_> OK so thats on my list of jobs - a low weight cutdoen cct
[23:51] <RocketBoy_> I'll stick that on the wiki
[23:52] <jcoxon> what else do we need?
[23:52] <RocketBoy_> A chute - but I can get that
[23:52] <jcoxon> okay
[23:53] <edmoore> we'll need a good way of accurately determining nozzle lift
[23:53] <RocketBoy_> yeah true
[23:53] <edmoore> as the weight of the payload is actually kind of irrelevent as long as it's not greater than the lift
[23:54] <RocketBoy_> actually what is needed is a strain gauge in the fill stem
[23:54] <edmoore> so if, as a for instance, we come in at 130g, it'd be good to have the fidelity to adjust the lift accordingly
[23:55] <jcoxon> instead of tins we could use water as the weight
[23:57] <RocketBoy_> I'll think on it - also we need to agree the cut-down and camera interfaces to the flight computer
[23:58] <jcoxon> okay well i'll start watching the weather and will attempt to adapt this cocoamodem code
[23:58] <jcoxon> might have to pick your brains RocketBoy_
[23:59] <edmoore> watching the weather?
[23:59] <jcoxon> yup
[23:59] <jcoxon> i'll start to keep an eye on the jetstream
[23:59] <edmoore> RocketBoy_: atm we have 3.3v io straight from the chip
[00:00] --- Fri Mar 28 2008