[Space] Audio

Albert Alexander albert.alexander at gmail.com
Fri Mar 19 10:56:34 PDT 2010


Can we feed the opentracker signal into the G1 mic jack and use it as a
trigger?

On Fri, Mar 19, 2010 at 10:43 AM, Greg Stramback <grog at piratelabs.com>wrote:

> Good point Nils.  It's kind of a shame we don't have the weight allowance
> that would allow for a centralized GPS based timing platform that could
> synchronize the clocks.  Eh, weight alone wouldn't be the problem anyways.
>  The expense is nothing to sneeze at.
>
> Besides, we're only using one device's data as a reference to compare the
> other with.  A reference packet every 4 mins will fit in nicely with the
> regular 30sec interval packet.
>
> -g-
>
> On Fri, Mar 19, 2010 at 8:51 AM, <nils at shkoo.com> wrote:
>
>> I think it'll be tough to avoid them interfering with each other except if
>> we have some kind of synchronization mechanism.
>>
>> I think that if we try to configure the clocks to be at the same rate,
>> we'll get pretty close but not exact. Then when they start interfering
>> with each other it will take longer for them to stop.
>>
>> I think the best thing to do would be to set the intervals as follows:
>>
>> opentracker: 31 seconds
>>
>> g1: 127 seconds
>>
>> Guestimating the transmit time as 1 second, that way they will only line
>> up on the same second once every 3937 seconds, so most of the beacons
>> should be fine even if the timing isn't exact.
>>
>> If we tried to line them up on 30 seconds and it ended up with the
>> following intervals:
>>
>> opentracker: 30 seconds
>> g1: 30.1 seconds
>>
>> Then when they line up, they would transmit on the same second for 10
>> beacons in a row, so we could lose a whole 5 minutes of transmitted data.
>>
>> Ideally, the thing to do would be to make them able to listen to telle
>> when the other is transmitting. I'm pretty sure the opentracker can do
>> collision avoidance of some sort, but the android code not so much right
>> now.
>>
>> -nils
>>
>> On Thu, 18 Mar 2010, Albert Alexander wrote:
>>
>> > Sounds right to me, but I'll defer to Nils. I know they do not transmit
>> > simultaneously.
>> >
>> > On Thu, Mar 18, 2010 at 8:44 PM, Christie Dudley <longobord at gmail.com
>> >wrote:
>> >
>> >> I think the idea we had was that they were each sending at the same
>> >> interval.  If they maintain even reasonably good clocks and aren't
>> aligned,
>> >> they shouldn't ever overlap.  I think their duty cycle is low enough
>> that
>> >> this wouldn't be a problem.
>> >>
>> >> (I'm assuming that you mean amateur radio, not an actual walkie-talkie,
>> >> here?)
>> >>
>> >> Christie
>> >> _______
>> >> "We also briefly discussed having officers replaced by very small shell
>> >> scripts." -- Noisebridge meeting notes 2008-06-17
>> >>
>> >> The outer bounds is only the beginning.
>> >> http://www.flickr.com/photos/genriel/sets/72157623376093724/
>> >>
>> >>
>> >> On Thu, Mar 18, 2010 at 6:24 PM, Albert Alexander <
>> >> albert.alexander at gmail.com> wrote:
>> >>
>> >>> Nope, they transmit at separate times. We could use a fet to switch
>> >>> sources but that's more parts and wires.
>> >>>
>> >>>
>> >>> On Thu, Mar 18, 2010 at 6:10 PM, Greg Stramback <grog at piratelabs.com
>> >wrote:
>> >>>
>> >>>> I'm making the assumption that we're expecting a certain percentage
>> of
>> >>>> garbled / unreadable packets due to two audio sources being combined?
>> >>>>
>> >>>> -g-
>> >>>>
>> >>>> On Thu, Mar 18, 2010 at 5:56 PM, Albert Alexander <
>> >>>> albert.alexander at gmail.com> wrote:
>> >>>>
>> >>>>> The walkie-talkie is getting audio from two sources. I suggested
>> using a
>> >>>>> splitter to combine the sources, but this will load down the output
>> >>>>> transistors unless we add two resistors in series before the
>> splitter. 10k
>> >>>>> is fine. This will attenuate the current of each signal. We could
>> use a
>> >>>>> summing amp if we want to avoid the attenuation, or we could just
>> turn up
>> >>>>> the volume.
>> >>>>>
>> >>>>> Will test G1 audio out AC coupling tonight after 5moF
>> >>>>>
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>> >>>>>
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>> >>>
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