The Eggfinder - A Low-Cost GPS/RF Tracking System

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The Eggfinder - A Low-Cost GPS/RF Tracking System

Postby SpaceManMat » Wed Feb 05, 2014 5:48 pm

Came across this on us forums

As many of you that have purchased Eggtimer altimeter kits know, I have developed a simple GPS/RF tracking system. It's called the Eggfinder, there's a transmitter that goes in your rocket and a receiver that stays on the ground. Basically, it streams NMEA 0183 serial GPS data to your ground device (laptop, tablet, possibly Android smartphone), and can be used to track your rocket in flight and more importantly to tell you where it went so you can get it back. You can use just about any mapping software with it that can take NMEA GPS data input; the only restrictions are what your device will handle.

The transmitter runs on the license-free 900 MHz band, the module that I use (the Hope RF HM-TRP) is the same one that's used in the popular 3DR radios. The firmware in the radio modules is Hope RF's standard firmware; this is to ensure that the radio complies with the FCC's spectrum requirements as tested by Hope RF.

Details are at http://www.eggtimerrocketry.com/page21.php , cost for the kit will be under $100. Availability should be sometime this Spring; I'm finishing up the documentation and waiting for parts.

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Re: The Eggfinder - A Low-Cost GPS/RF Tracking System

Postby matthew » Wed Feb 05, 2014 9:26 pm

I'm in. $100 isn't that much for electronics in this hobby, and the Eggtimer wasn't any trouble to build (but I haven't flown it yet). Interestingly, Keith Packard from Altus Metrum panned the Sirf 3 chip for rocketry use (slow lock time during flight). Not sure if the Sirf 4 used in the Eggfinder is any better.

I've been trying to decide on a tracker in time for Thunda, and I'm currently leaning towards the BRB900 system. I shouldn't need to buy it until late this year, so I should have a chance to try out the Eggfinder first.
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Re: The Eggfinder - A Low-Cost GPS/RF Tracking System

Postby matthew » Sun Mar 30, 2014 12:47 pm

Cris Erving is now shipping these to Australia. Shipping cost is US$20 (makes it US$110 shipped). Frequencies 917Mhz-927Mhz in 2Mhz steps. If a group is interested, it might be worth coordinating to make sure you get different frequencies.
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Re: The Eggfinder - A Low-Cost GPS/RF Tracking System

Postby SpaceManMat » Sun Mar 30, 2014 8:08 pm

Count me in for a starter kit and the optional RP-SMA edge connectors (not sure i will use it yet but will grab one for convenience). Might also be able to save on shipping?
QRS: 124
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Re: The Eggfinder - A Low-Cost GPS/RF Tracking System

Postby matthew » Mon Mar 31, 2014 9:46 pm

I've been given the nod to get one. There's probably not much saving on shipping for me in a group buy, as I'd have to get it up from Brisneyland.

I've just ordered one of these for the Bluetooth connection.
http://www.banggood.com/HC-06-Wireless- ... 08617.html

I'm eyeing off this battery to make a handheld ground station (with Jaycar case).
http://www.hobbyking.com/hobbyking/stor ... ouse_.html

And this one for the transmitter.
http://www.hobbyking.com/hobbyking/stor ... ouse_.html

Will also get the RP-SMA connectors.
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Re: The Eggfinder - A Low-Cost GPS/RF Tracking System

Postby vk2icj » Tue Apr 01, 2014 2:49 am

matthew wrote:Cris Erving is now shipping these to Australia. Shipping cost is US$20 (makes it US$110 shipped). Frequencies 917Mhz-927Mhz in 2Mhz steps. If a group is interested, it might be worth coordinating to make sure you get different frequencies.



Not to be a fun Nazi :twisted:

But I don't think 900mhz is the best band to be using for finding your lost rocket. 900mhz is in one of the mobile phone bands here in Oz. You would want to do a freq scan at the location you are intending to fly with these. If there is a mobile tower in the area it could obliterate your rx. An old analogue scanner would do the trick just to see if the freqs are clear or not. If you have an expensive rocket I would go with one of the UHF BRB products from Blake and get a Foundation lic (easy as) to ensure you got your telemetry back from the rocket.

Just my .02

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Re: The Eggfinder - A Low-Cost GPS/RF Tracking System

Postby matthew » Tue Apr 01, 2014 7:15 am

Apparently between 915Mhz and 928Mhz is open for consumer electronics. I believe this is the band that the "tweaked for Australia" BRB900 products operate in. I believe the developer of the Eggfinder went with the 900Mhz range as it's less crowded than other unlicensed bands, and that users wouldn't need to get licensed to use the products. As an aside, I looked into the license. They practically give you everything you need to know on the website, but it's an annual fee, not just a once off, which personally puts me off somewhat. As to efficiency and range, well, it's a hundred bucks Vs many hundreds of dollars. Do your research, belly up to the bar, and run what ya' brung. ;)
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Re: The Eggfinder - A Low-Cost GPS/RF Tracking System

Postby ROCKet STAR » Tue Apr 01, 2014 11:36 am

Looking at the datasheet for the radio modems that the Eggfinder uses, it appears that the frequency is programmable accross the band, so choosing your own frequency should be fairly simple, and it would ensure that you stay above 915MHz.

http://hoperfusa.com/docs/HM-TRP.pdf

It is worth also noting that the datasheet also indicates that there is a 433MHz version of the radio modem available, so somebody licensed to use th 433MHz band, could probably just substitute the modem in the kit for a 433MHz modem, and swap the antenna for a 433MHz antenna. 433MHz would probably also give improved range. Looking on ebay, the modems themselves appear to be selling for <$10.

I'm interested to hear what kind of range people get with these. While the modems lack some of the nice features of those used in the more expensive GPS telemetry units like frequency hopping spread spectrum, addressing and error correction, for the price, they look very attractive! :)
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Re: The Eggfinder - A Low-Cost GPS/RF Tracking System

Postby vk2icj » Tue Apr 01, 2014 12:17 pm

Like I said I am not the fun police by any means, trust me. In fact I am quite the opposite. Australia is way too restrictive in my opinion on just about everything. That being said I have been a ham for over 20 years now so I do have a good idea of how radio works. The main jist of my post is that even though one can technically use 915 to 928 it may not be the best option if you have an expensive rocket on the "finding side" The Department of Defence is also allocated to use that portion btw along with general consumer items at less than 1watt. UHF 430mhz is for Hams only. Even if the mobile phone towers are not specifically on 915 to 928 if they are in the area your front end will be overloaded and your rx will not work. Not to mention if someone next to you makes or receives a phone call that too could interfere. Hence in my first post I think it would be prudent to test your flight area with a scanner prior to flight to see if there is a clear clean portion of bandwidth to fly or if there is interference from anything. Just because the Mobile tower is not specifically on 915 to 928 doesn't mean a few mhz away will not bleed over in the area these devices work on. I am into RC aircraft as well and for the last year and half been getting into FPV (first person view) alot of the guys in the states use 900 mhz for a number of good reasons. They don't have the lic'd telstras above and below them on the bandplan. Here in Oz for the most part the video is interfered with if you are anywhere near a mobile tower or can see one on the horizon. So almost no one uses 900mhz.

Yes the Ham lic cost money to keep here in Oz. I really think that is a rort lol. I also hold a lic in the US which is free and renewable every 10 years not annually but that is Australia. :wink:

I intend on having a portable Packet station at Thunda next year which will track any rocket using BRB on the packet freqs using APRS. This means that any number of rockets can be in the air and all the ground stations can rx thier position and reflect it to other stations. IE if my station hears the rocket and decodes the packet and the rocket's owner does not because of bad antennas or what ever, my station will repeat the packet so that the owner will hear it too. Very handy especially if you have different people using different antennas or hand held radios with very limited antennas.

If your hellbent on running 900mhz you might want to look into some antenna options to increase your rx signal. Here are some directional antennas used in the same band for FPV.

http://www.readymaderc.com/store/index. ... h=11_45_47

I would opt for the RP SMA option with the Eggfinder for sure. The wire antenna for sure will degrade your rx ability over distance, especially if your polarization is off with the tx. Laptops and computers for that matter are notoriously rf noisy so having a good rx antenna is paramount.

I am interested if you guys have any success with these Eggfinder units. They look good. My concerns are solely over the fact that FPV here in Oz using the same freqs is all but dead because of interference from mobile towers. Loss of video when flying your plane at a distance usually means loss of aircraft, though with Return to Home GPS these days it is a bit better sorry off topic. I would still suggest though that if you have an expensive rocket and want it back the best option is the BRB or Telemetrum from Blake along with spending 70 some dollars a year to keep a ham lic. You might even find the radio bit fun

Cheers

Chris
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Re: The Eggfinder - A Low-Cost GPS/RF Tracking System

Postby vk2icj » Tue Apr 01, 2014 12:45 pm

Hey Chris

I just had a look at the website you posted. Interesting. They are using FSK for the modulation. But like you said has the Achilles heel without freq hopping if anything is interfering with a binary signal you will lose data. To me the 433 version would be heaps better for propagation, of course you need the Ham ticket then too. Which is not hard nor really that expensive when we look at how much we spend on Rockets each year for Ap which goes up in seconds lol.

Cheers

Chris


ROCKet STAR wrote:Looking at the datasheet for the radio modems that the Eggfinder uses, it appears that the frequency is programmable accross the band, so choosing your own frequency should be fairly simple, and it would ensure that you stay above 915MHz.

http://hoperfusa.com/docs/HM-TRP.pdf

It is worth also noting that the datasheet also indicates that there is a 433MHz version of the radio modem available, so somebody licensed to use th 433MHz band, could probably just substitute the modem in the kit for a 433MHz modem, and swap the antenna for a 433MHz antenna. 433MHz would probably also give improved range. Looking on ebay, the modems themselves appear to be selling for <$10.

I'm interested to hear what kind of range people get with these. While the modems lack some of the nice features of those used in the more expensive GPS telemetry units like frequency hopping spread spectrum, addressing and error correction, for the price, they look very attractive! :)
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Re: The Eggfinder - A Low-Cost GPS/RF Tracking System

Postby matthew » Tue Apr 01, 2014 9:39 pm

Westmar is apparently 40 odd kms from Meandarra, so I'm -assuming- there won't be much in the way of mobile phone or military signals to cause interference. For the price, the EF is just another string in the bow for rocket location. I'll certainly be doing some tests in town before putting any faith in it.

All good info, though. It's good to know what we're up against when using radio devices, especially as an amateur. I wouldn't say I'm "hellbent on running 900Mhz", but I am keen to try out an inexpensive tracking option. The fact it's in kit form adds to the hobby appeal, too. :)

I'm looking forward to seeing your setup at Thunda. :D
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Re: The Eggfinder - A Low-Cost GPS/RF Tracking System

Postby vk2icj » Tue Apr 01, 2014 11:26 pm

matthew wrote:I'm looking forward to seeing your setup at Thunda. :D



Yeah should be good. We are taking our caravan up for the launch and will be using that as a base station lol. I intend to have a tracking station in a watertight case like the Pelican cases. It should be able to just flip open turn on and start tracking rockets against a map. Well that is the plan anyway. It will probably turn into a pile of wires and gadgets lol.

I might start another thread to see how many hams are coming to the launch. To start co ordinating freqs and the like. I have spoken to one overseas ham already planning on attending so it is probably time to start thinking these things out.

Cheers

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Re: The Eggfinder - A Low-Cost GPS/RF Tracking System

Postby ROCKet STAR » Wed Apr 02, 2014 12:46 am

matthew wrote:Westmar is apparently 40 odd kms from Meandarra, so I'm -assuming- there won't be much in the way of mobile phone or military signals to cause interference. For the price, the EF is just another string in the bow for rocket location. I'll certainly be doing some tests in town before putting any faith in it.

All good info, though. It's good to know what we're up against when using radio devices, especially as an amateur. I wouldn't say I'm "hellbent on running 900Mhz", but I am keen to try out an inexpensive tracking option. The fact it's in kit form adds to the hobby appeal, too. :)

I'm looking forward to seeing your setup at Thunda. :D


For what it's worth, I have built two different 900MHz GPS systems, and not had an interference issue with either (including within the Sydney basin). Both do use frequency hopping, however. I know that from my recent visit to Westmar, that mobile coverage is pretty sketchy anyway, so you should be ok. I think your biggest issue will be other flyers using the 900MHz band.

Not sure whether you are going to be at Westmar this June? but I'll have a 1W 900MHz setup with me. Running them side by side could make for a good test to see if there are any issues with it.
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Re: The Eggfinder - A Low-Cost GPS/RF Tracking System

Postby vk2icj » Wed Apr 02, 2014 5:13 am

ROCKet STAR wrote:
matthew wrote: but I'll have a 1W 900MHz setup with me. Running them side by side could make for a good test to see if there are any issues with it.



Gee that has some umph.. I started a thread for amateurs in the Thunda section. I imagine someone will organise the feqs and times but hopefully there will be windows to test equipment and windows with no testing and only flying. UHF BRB will work seamlessly on APRS but I am not sure of the 900mhz units.

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Re: The Eggfinder - A Low-Cost GPS/RF Tracking System

Postby OverTheTop » Fri Apr 11, 2014 8:35 pm

Recently received my kits from Chris at Eggtimer Rocketry. Great to deal with. Very fast delivery of the kits.

I have thrown them together in the past two days. Being largely through-hole components I thought they were quite quaint as I have been using surface-mount for most of the last 15 years so. The THT resistors were slightly confronting :-) The last time I designed a product with a through-hole resistor was back in 2000.

The kits went together nicely. Documentation is designed so anyone who might be able to wield a soldering iron has a good chance of making it work.

I did actually change some of the through-hole parts (resistors, LEDs, some capacitors) to surface mount along the way. They might tolerate the high-Gs a little better.

Both Tx and Rx worked first shot and produced data on the PC.

Nice and skinny so it fits in a 24mm BT.

I'll post some pics over the weekend.
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