highaltitude.log.20081214

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[05:10] <natrium> hey edmoore
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[12:28] <rjharrison> MOrning all
[12:29] <rjharrison> PING edmoore
[12:29] <edmoore> yo
[12:29] <rjharrison> Quick question if I may
[12:29] <rjharrison> I have PWM working lovely
[12:29] <edmoore> cool
[12:30] <rjharrison> However this still gives me the same problem with the flicking between the two voltages
[12:30] <rjharrison> Is that where the filter comes in
[12:30] <edmoore> correct
[12:31] <rjharrison> The PWM basically does the same as my two resistor approach
[12:31] <rjharrison> But with less components. IE none
[12:31] <rjharrison> and using only one pin
[12:31] <edmoore> yeah - the duty cycle (on/off ration) sets the voltage
[12:31] <rjharrison> Yep
[12:32] <edmoore> and the low pass filter gets rid of the pulsing effect
[12:32] <edmoore> hang on one sec...
[12:33] <edmoore> nope, can't find what I'm looking for
[12:33] <rjharrison> I have read a lot about LPF's but i'm buggered if I can get it off the ground.
[12:33] <rjharrison> I need a cap and a resistor
[12:33] <gordonjcp> that's a low pass filter
[12:33] <gordonjcp> well
[12:33] <gordonjcp> it is if the cap goes to ground
[12:33] <edmoore> I'm about to have sunday lunch, but I will nail this one of the head this afternoon
[12:33] <gordonjcp> if the cap is in series and the resistor goes to ground, it's highpass
[12:34] <rjharrison> Ok
[12:35] <rjharrison> So if I want to remove the noise when switching voltages quickly at ~100 BAUD I'm last as to what I want to do
[12:35] <rjharrison> So if I want to remove the noise when switching voltages quickly at ~100 BAUD I'm lost as to what I want to do
[12:35] <rjharrison> s/last/lost :)
[12:35] <gordonjcp> rjharrison: well, what exactly *are* you trying to do?
[12:37] <rjharrison> I'm sending two voltages to a radiometrix to send 1's and 0's at 100 BAUD and I want to clean up the signal before sending it
[12:37] <edmoore> trying to filter out the pwm but not the rtty
[12:37] <edmoore> rjharrison: what frequency is the pwm at?
[12:38] <rjharrison> Very high 8000000/100
[12:38] <rjharrison> 80000 Hz
[12:38] <rjharrison> 80kHz :)
[12:39] <edmoore> cool
[12:39] <gordonjcp> so you don't need much of a lowpass filter then
[12:39] <rjharrison> True
[12:39] <edmoore> so think of an rc filter as adding inertia to a an alactric circuit
[12:39] <edmoore> electrical*
[12:39] <rjharrison> I'm with you
[12:39] <edmoore> it's like punching an open door
[12:40] <rjharrison> Yep Ouch
[12:40] <edmoore> you can thump it, but it doesn't slam shut, it just moves a bit
[12:40] <edmoore> so the resistor and capacitor act like a big 'mass;
[12:40] <edmoore> mass*
[12:40] <rjharrison> Ok
[12:41] <edmoore> so you can bash it with the pwm voltages, but it won't instantly move to whatever voltage you give it
[12:41] <edmoore> it takes time to get there
[12:41] <edmoore> imagine you're standing my your light switch
[12:41] <edmoore> you turn the light on, then off
[12:41] <rjharrison> by
[12:41] <edmoore> you do that once per second
[12:41] <rjharrison> yep
[12:41] Last message repeated 1 time(s).
[12:41] <edmoore> you see the light go on then off
[12:41] <rjharrison> yep
[12:41] <edmoore> the you speed it up a bit - on then off 10 times a second
[12:41] <rjharrison> yep
[12:42] <rjharrison> and so on till its a blur
[12:42] <edmoore> you see the bulb brighten and dim, brighten and dim, pretty fast, but never felly heating up or colling down
[12:42] <rjharrison> yep
[12:42] <edmoore> then you up that to 100 times a second
[12:42] <edmoore> the light bulb doesn't have time to completely heat up and cool down each time, it just 'glows'
[12:42] <rjharrison> Untill it aproximates a constant
[12:42] <gordonjcp> rjharrison: look at how audio stuff works
[12:42] <edmoore> if you are doing 5ms on, 5ms off, the bulb will just 'glow' at 50% brightness
[12:43] <rjharrison> Yep PWM
[12:43] <rjharrison> 50% duty
[12:43] <edmoore> it's exactly the same idea with adding the low pass filter - it doesn't have time to completely respond to the 5V, 0V, 5V, 0V switching
[12:43] <edmoore> it has too much 'inertia' so it just outputs the avergae value
[12:44] <rjharrison> Ie rmoving the effect of the noise
[12:44] <edmoore> well, to be technical, noise (white noise) is present at every frequency
[12:44] <edmoore> you're just getting rid of the frequencies you don't want
[12:45] <edmoore> http://en.wikipedia.org/wiki/Low-pass_filter
[12:45] <edmoore> take a look at the first graph
[12:45] <rjharrison> Yep read that
[12:45] <rjharrison> Looking
[12:45] <edmoore> so you see it lets through 'unattenuated' (untouched) everything up to about 1 rad/sec
[12:46] <rjharrison> vlotage drops off as freq increases
[12:46] <edmoore> then as the freq increases, it starts reducing the output relative to the input
[12:46] <edmoore> yep
[12:46] <edmoore> gain is output/input
[12:46] <edmoore> so your rtty signal has two main freq components
[12:47] <edmoore> one is 100hz - the rtty
[12:47] <edmoore> the other is 80khz - the pwm freq
[12:47] <rjharrison> Yep
[12:47] <edmoore> your RC filter needs to have a 'cutoff' freq (see graph) somewhere between the two
[12:47] <edmoore> I would say, 500hz
[12:48] <edmoore> so the 100 hx rtty is let through pretty much untouched, but the pwm is very heavily attenuated
[12:48] <edmoore> now i have to go to lunch - but the task now is to find the forumula for the cutoff freq of an rc filter
[12:49] <edmoore> tis easy - gordonjcp?
[12:49] <edmoore> bbl
[12:49] <gordonjcp> edmoore: yeah
[12:49] <gordonjcp> "select on test"
[12:49] <rjharrison> 3KR + 0.1UF
[12:49] <gordonjcp> sounds good
[12:49] <gordonjcp> try it and see
[13:01] <rjharrison> Seems to work
[13:01] <rjharrison> :)
[13:24] <edmoore> back
[13:41] <rjharrison> Am I ment to be pulse shaping?
[13:41] <edmoore> you don't have to just yet
[13:41] <edmoore> but tat would be the reason to go pwm
[13:42] <rjharrison> I think that was the bit I was hoping to get from the pwm / dac
[13:42] <edmoore> so that's the next step
[13:44] <rjharrison> ok as i can't see any dif between the pwm and my pin approach
[13:44] <edmoore> there isn't one currently
[13:44] <rjharrison> but that makes sense atm
[13:44] <rjharrison> :)
[13:44] <rjharrison> sorry baby in arms
[13:45] <rjharrison> bit slow typing
[13:57] <rjharrison> Hum not sure if I will be able to pulse shape with pwm there are only 10 steps between the two freq
[14:00] <rjharrison> I'm not sure I know what pulse shaping is. It's the way you vary the voltage between the two points
[14:01] <rjharrison> Right I'm off to the ball park will be back on in a bit
[14:14] <rjharrison> Back on in 15 mins
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[14:40] <rjharrison_> At the ball park
[14:43] <rjharrison_> edmoore: Pulse shapeing is basically how you jump between the the max and min voltages. I'm guessing it's the duration you send the voltages between the max and min point.
[14:47] <rjharrison_> if 0 and 9 are the min and max then something like 00011345688999
[14:48] <rjharrison_> gordonjcp does that make sense to you?
[14:49] <gordonjcp> well kind of
[14:49] <gordonjcp> I wouldn't bother tvh
[14:49] <gordonjcp> tbh
[14:50] <rjharrison_> 'cos the improvement isn't worth the effort?
[15:03] <gordonjcp> well, try it and see
[15:03] <gordonjcp> I think the "blurring" of the transition might well make it harder to get a good clean decode
[15:04] <gordonjcp> you may find that going 0/5/9 is enough to limit the "keyclicks"
[15:04] <gordonjcp> I'd be really interested to see how you get on with it
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[15:12] <rjharrison_> gordonjcp: Ok I'll feed the results back
[15:13] <rjharrison_> Bidding on an occiloscope at the moment
[15:13] <gordonjcp> cool
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[17:11] <Laurenceb> http://news.bbc.co.uk/1/hi/world/europe/7778767.stm
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[18:10] <rjharrison> gordonjcp if I can do rtty at 300 baud then I think I probably don't need to do any pulse shaping
[18:27] <rjharrison> gordonjcp if I can do rtty at 1200 baud then I think I probably don't need to do any pulse shaping
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[18:44] <rjharrison> edmoore if I can do rtty at 1200 baud is it fair to say that I'm not going to need to pulse shape
[18:44] <edmoore> yes
[18:45] <rjharrison> Good
[18:45] <rjharrison> That just using the 2 pin
[18:46] <rjharrison> RTTY at 1200 is about 99.9% correct with no antenna
[18:46] <edmoore> i bet the error rate will rise up in the air :)
[18:49] <rjharrison> Sure I'll never send it out at that
[18:49] <rjharrison> 50 baud will do me just fine
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[20:03] <Laurenceb> hi steve
[20:03] <G8KHW> yo
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[20:59] <Laurenceb> G8KHW: pulse shaping isnt too inportant if the bandwidth of your ADC/radio is much greater than the baud rate?
[21:31] <G8KHW> yes thats true in terms of will you receive all the energy - but on the downside with a wide bandwidth you are also taking in extra noise therefore degrading the signal to noise ratio
[21:33] <G8KHW> so pulse shaping is all about confining the energy to a small bandwidth to allow you to reduce the receiver channel bandwidth
[21:55] <Laurenceb> ah yeah
[21:55] <Laurenceb> so how does OFDM work then?
[21:55] <Laurenceb> does that use pulse shaping?
[21:59] <Laurenceb> oh I think I get it: the spreading across bandwidth doesnt matter as you are using bandwidth across multiple channels anyway
[22:01] <Bluenarf> Laurenceb, care to do a favour?
[22:01] <Bluenarf> http://donegal.paulsnet.org
[22:01] <Bluenarf> what does that give you?
[22:02] <Laurenceb> Apache 2 Test Page
[22:03] <Bluenarf> aha
[22:03] <Bluenarf> http://donegal.paulsnet.org/zm
[22:03] <Bluenarf> user:guest pass:guest
[22:03] <Bluenarf> that work?
[22:04] <Laurenceb> seems so
[22:04] <Laurenceb> I'm logged in
[22:04] <Bluenarf> try clicking test2
[22:04] <Laurenceb> oh
[22:04] <Laurenceb> hello
[22:05] <Laurenceb> I cant see anyone
[22:05] <Bluenarf> you see a camera?
[22:06] <Laurenceb> yes
[22:06] <Laurenceb> wave
[22:06] <Laurenceb> ?
[22:06] <Laurenceb> ah hi there
[22:07] <Laurenceb> cut your hair
[22:08] <Laurenceb> seems to work
[22:11] <Bluenarf> it works? :D
[22:11] <Bluenarf> ok, click montage
[22:11] <Bluenarf> top rightish
[22:12] <Bluenarf> you have 2 cams?
[22:12] <Bluenarf> ill walk, tell me how smooth it is
[22:12] <Bluenarf> is it like a freame every few seconds, or a pretty smooth feed?
[22:12] <Bluenarf> me?
[22:12] <Bluenarf> :P
[22:12] <Bluenarf> hmm, the whole thing has jammed up on my side
[22:16] <rjharrison> Who is G8KHW?
[22:16] <rjharrison> Is that rocketboy?
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[22:17] <EI5GTB> feckin internet crapped out
[22:17] <EI5GTB> was it a fairly smooth stream? i.e > 1fps
[22:20] <EI5GTB> Laurenceb,
[22:21] <Laurenceb> sorry
[22:21] <Laurenceb> was afk
[22:22] <EI5GTB> np
[22:22] <Laurenceb> ok I'll go to the montage
[22:22] <Laurenceb> no nudity
[22:22] <EI5GTB> :P
[22:22] Action: EI5GTB puts his cloths back on
[22:23] <Laurenceb> I see you
[22:24] <Laurenceb> looks good
[22:24] <Laurenceb> a bit glitchy
[22:24] <Laurenceb> you move about 50cm between frames
[22:24] <Laurenceb> it might be my machine
[22:24] <Laurenceb> I'm on ubuntu atm
[22:25] <EI5GTB> smooth?
[22:25] <EI5GTB> like 2 or 3 frames a second?
[22:25] <Laurenceb> it updates scrolling from top to bettom
[22:25] <Laurenceb> yeah, easily that fast
[22:25] <Laurenceb> how does it work?
[22:25] <EI5GTB> i see
[22:26] <Laurenceb> is it using gifs?
[22:26] <EI5GTB> how many frames a second?
[22:26] <EI5GTB> ffs, has my internet crapped out again
[22:26] <Laurenceb> ok you can stop moving around :P
[22:26] <Laurenceb> ~5
[22:27] <Laurenceb> I'm turning it off now to save bandwidth
[22:27] <Laurenceb> does it use GIFs ?
[22:29] <Laurenceb> as I think ubuntu has issues with large GIFs
[22:29] <Laurenceb> may explain the scrolling stuff
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[22:29] <Laurenceb> hello
[22:29] <Laurenceb> does it use GIFs ?
[22:30] <Laurenceb> as I think ubuntu has issues with large GIFs
[22:30] <Laurenceb> may explain the scrolling stuff
[22:30] <EI5GTB-Crapnet> grrr, my internet keeps dropping out???
[22:30] <Laurenceb> yeah
[22:30] <EI5GTB-Crapnet> yea, its like mpegs or jpegs or somthing im not all that sure
[22:30] <Laurenceb> hmm
[22:30] <Laurenceb> it looks maybe like a series of gif animations to me?
[22:32] <EI5GTB-Crapnet> twas jpegs
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[22:32] <EI5GTB-Crapnet> iv set it to mpeg now for the fun
[22:32] <Laurenceb> ok
[22:37] <EI5GTB-Crapnet> grr, i dont have the mpeg strreamer installed on the server properly
[22:37] <EI5GTB-Crapnet> ffs
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[22:43] <rjharrison> Yo natrium42
[22:43] <rjharrison> How you doing>
[22:43] <rjharrison> ?
[22:44] <rjharrison> I have been playing with RTTY and avr'S
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[22:46] <rjharrison> Right it's nearly night time for me
[22:46] <rjharrison> !last jcoxon
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[22:50] <Laurenceb> I'm going to get an early night
[22:50] <Laurenceb> cya all
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[00:00] --- Mon Dec 15 2008