PICAXE is in Space

S

srnet

Senior Member
MFB said:
Just thought that another advantage of the $50SAT communications approach would the ability to receive data using low cost rf receivers, that do not normally support the SSB mode normally used by UKHAS flights. However, no reason why $50SAT communications technology would not be compatible with the existing international tracking network at a lower entry cost.
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Well for distances to a balloon of circa 250kM, even the humble RTL DVB TV dongle should be able to pick up FSK RTTY at 10mW.

That would be with an omni directional antenna, but as a balloon is more or less in one location, even a simple home brew yagi would get a lot further.

What the £5 RFM22B can do, slow Morse, fast Morse, telemetry and FSK RTTY, is just fine for most applications, and it does them well.

There are indeed some exotic comms modes out there, which would give better range, but would require a different radio as the RFM22B cannot do AFSK, nor can it (without significant modification) do precise or small FSK shift either.

I would approach a small lightweight HAB tracker in the same way as I did with $50SAT, find a small light radio transceiver, that will do the basics and then work out how to best use it.
 
M

MFB

Senior Member
A range of 250kM might be surprising useful for long duration flights. The Spacenear site shows balloons being tracked by internet connected receiving sites located much less that 500kM apart. Although the density currently decreases rapidly once outside of Europe airspace, the availability of low cost SDR receiving dongles might soon extend the tracking network further south and east. There only remains the problem of sea crossings.
 
S

srnet

Senior Member
S

srnet

Senior Member
Yes, Slow FM Morse.

With the summer nearly with us, $50SAT has been out of eclipse long enough that towards the end of the pass over the UK its warmed up enough for the Morse to switch to a slower rate.

I first heard the slow rate as it passed over the Algeria coast about a month ago.
 
S

srnet

Senior Member
I did in particular like this bit of the article;

"The extremely clever flight software, entirely written in PICAXE BASIC, manages to trick the RFM22 into radio modes it was never designed for, such as FM morse, FSK RTTY, and native RFM22 packets."
 
S

srnet

Senior Member
The battery has degraded, lost voltage, considerably.

Its now been through around 3000 charge discharge cycles, and the same number of times being cycled between +30C to -30C, so as it was just a standard small camera battery, the type you get on eBay, its a wonder its survived so far.

There is a file on the dropbox;

https://www.dropbox.com/sh/l3919wtfiywk2gf/AADD3eoHItoPbPl-zZ_-Pclaa/Telemetry-Reports-2014-06-22.txt

Which shows the decline, the battery voltage is the last item before the * and checksum.

In the first week on operation the lowest battery voltage seen was 3723mV (its lower in the cold), and recently the lowest has been arounf 3501mV.

Once its warmed up and is under charge, the voltage is up to 3662mV or so.

The transmit is turned off when the voltage falls bellow 3300mV, so it may well keep going for a while yet.

And before anyone says 'could you not have used a better battery', appreciate there just is no decent information available on very small batteries suitable for this type of application. Not suprising really, no one had had tried to use this type of simple battery to power a satellite until $50SAT came along.
 
S

srnet

Senior Member
MFB said:
Would a super capacitor have been able to 'fit' the requirement?
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Not really, not enough voltage for long enough to power the transmitter, which takes around 85mA.

Not much good in the dark part of the orbit either.

It was tried, and discounted because of the problems.
 
S

srnet

Senior Member
Quote;

The BATC will webstream AMSAT-UK International Space Colloquium at the Holiday Inn, Guildford, GU2 7XZ, UK on July 26-27

http://amsat-uk.org/2014/07/23/batc-to-webstream-space-colloquium/

This year we are fortunate to have Stuart Robinson GW7HPW attending the Colloquium and he will be giving a presentation on $50SAT at 4:05pm BST (1505 GMT) on Saturday, July 26.

The Colloquium is open to all, admittance is £10 payable on the door, for those wishing to attend further information is at http://amsat-uk.org/colloquium/colloquium-2014/
 
S

srnet

Senior Member
The presentation went well, there was a great deal of interest in our little PICAXE powered satellite.

The working model in particular, everyone wants to get there hands on it.

The presentation, video and slides can be found here;

http://amsat-uk.org/colloquium/colloquium-2014/presentation-videos/

There will be another $50SAT presentation at the UKHAS conferance;

http://ukhas.org.uk/general:ukhasconference2014

This one will focus more on the RFM22B radio, and how this £3 device was turned into a reliable satellite communications system.
 
S

srnet

Senior Member
Thank you for the kind words.

It looks like my US colleagues, Michael and Howie may be doing a $50SAT presentation at the US AMSAT symposium your side of the Pond (yes I know America is a big place);

http://www.amsat.org/?page_id=1555

As soon as its confirmed I will post an update.
 
A

Armp

Senior Member
Probably can't make it to Baltimore - grandsons birthday conflict!
But I may be in Cardiff early Sept if you're up for a pint?
 
S

srnet

Senior Member
UK High Altitude Society - $50SAT Presentation

If you want to watch it goto here;

http://www.batc.tv/

Select ‘Film Archive’ on the left.

In the drop down list under ‘Film Archive’ select ‘UKHAS 2014’ and click on the ‘Select Category’ button.

In the drop down list below, select ‘UKHAS2014 2 $50SAT’ and click on the ‘Select Stream’ button.


Stuart Robinson
GW7HPW
 
S

srnet

Senior Member
Well if you like to spend your time working on this sort of stuff, starting a Kickstart type project so other people pay your wages, with no guarantee you ever need to deliver anything, is one way of making a living.

Register a domain name, put up a glossy web site and the money starts to roll in.
 
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Buzby

Buzby

Senior Member
Absolutely brilliant ! Well done.

How is the little fella getting on ?. Is the battery keeping up ?
 
S

srnet

Senior Member
Battery is low, at around 3.52v, but its been stable for a couple of months.

Considering its been through around 5,500 mini charge cycles, its a wonder its lasted this long.
 
hippy

hippy

Technical Support
Staff member
Congratulations on that superb achievement. Have you calculated how many miles it has travelled during its year of being up there ?
 
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