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Author Topic: Yet another APRS Board  (Read 1948 times)
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Salem, Oregon
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Hey All-

Here is my latest creation, a small APRS Tracker board based on the Trackuino project (http://www.trackuino.org/).

The idea was to provide a low-cost tracker board that has some off-board sensor capability (the board requires 6V input and has a single on-board LM60 sensor but support is provided for 2 off-board sensors).

The on-board GPS is the SkyTraq SUP500R, which while supplying 3.3V signals can be powered by 3v-5v.

I do confess to using the auto-router (which is akin to pledging allegiance to Satan I guess) but I'd be interested in any suggestions for any improvements (or error corrections) I could make for the next version.

Thanks,

Brad (KF7FER)


* miniTrackuino.jpg (120.68 KB, 500x328 - viewed 71 times.)

* miniTrackuinoSCH2.png (96.1 KB, 979x799 - viewed 59 times.)

* miniTrackuinoBRD2.png (265.06 KB, 845x328 - viewed 50 times.)
« Last Edit: December 05, 2011, 01:21:41 am by Brad Burleson » Logged

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That RF trace looks like it wanders a long way (relatively speaking) before it gets to the SMA connector.  It needs to be closer to the RF pin of the radio module to avoid problems.

Rather, it would wander a bit, if it were actually connected...

Looks like you got bitten by the eagle "feature" where it looks like a wire is connected, but it isn't actually connected. the RF out isn't actually connected to the radiometrix footprint.

Since you appear to already have your boards fabbed, you can use a short piece of small coax (e.g. RG174) to jumper from the header to the SMA.

-j
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Salem, Oregon
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That RF trace looks like it wanders a long way (relatively speaking) before it gets to the SMA connector.  It needs to be closer to the RF pin of the radio module to avoid problems.

You're exactly correct, thanks.  When I resized the board (it was much wider with a DIP Atmega) I flipped the radio 180 degrees and forgot to move the SMA connector.  D'oh!

Rather, it would wander a bit, if it were actually connected...

Looks like you got bitten by the eagle "feature" where it looks like a wire is connected, but it isn't actually connected. the RF out isn't actually connected to the radiometrix footprint.

And this is even worse!  So the antenna connector went straight to ground.  I was surprised in my initial testing that while my home APRS station could receive the packet, the local iGate (5miles away or so) didn't see it.  I had put this down to me using a small rubber duck for my test and that I would try it again later with a decent antenna.

The problem is so obvious too looking at the finished board.  I'm embarassed.  I quickly went back thru the dozen or so board variations I'd created and was relieved that this was a new "enhancement" that I'd added.

It really does pay to go thru a schematic and "shake" each part with the move tool to make sure it's connected exactly as you expect - this isn't the first time I've been so bitten.  I believe there is a similar problem near the VR as well <sigh>

Since you appear to already have your boards fabbed, you can use a short piece of small coax (e.g. RG174) to jumper from the header to the SMA.

-j


Good idea.  But I did only have 3 made ($14 worth) and I wanted to find a better mounting solution for the GPS at any rate:  I'd like to find a pair of connectors I can use to mount the GPS on-board as well as inserting a cable in-between (and something a little more robust than a pair of 0.1" connectors).

BTW do you think it would be wise to increase the size of the RF trace? 

Thanks again for your feedback,

Brad (KF7FER)
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Quote
I'd like to find a pair of connectors I can use to mount the GPS on-board as well as inserting a cable in-between (and something a little more robust than a pair of 0.1" connectors).

What about a board to board connection, no cable? Samtec makes a 0.1" socket (web site drawing ) that may fit the bill - it would allow that header on the GPS to plug in through the board, so the GPS mounts flat.  I don't have any experience with this particular connector, but I've got a device that has a similar 2mm version of this thing, and it makes for an incredibly low profile mount. If you want to break it out, I'd do it by adding a connector to the PCB (if I understand what you're trying to accomplish, that is).

Quote
do you think it would be wise to increase the size of the RF trace?

What I know about RF PCB layout would fit in a gnat's navel.  If it were me, I'd put the connectors as close together as possible, so that my ignorance had limited impact. smiley-neutral

-j
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Quote
I'd like to find a pair of connectors I can use to mount the GPS on-board as well as inserting a cable in-between (and something a little more robust than a pair of 0.1" connectors).

What about a board to board connection, no cable? Samtec makes a 0.1" socket (web site drawing ) that may fit the bill - it would allow that header on the GPS to plug in through the board, so the GPS mounts flat.  I don't have any experience with this particular connector, but I've got a device that has a similar 2mm version of this thing, and it makes for an incredibly low profile mount. If you want to break it out, I'd do it by adding a connector to the PCB (if I understand what you're trying to accomplish, that is).

I'll have to take a close look at the Samtec stuff - interesting. 

Quote
do you think it would be wise to increase the size of the RF trace?

What I know about RF PCB layout would fit in a gnat's navel.  If it were me, I'd put the connectors as close together as possible, so that my ignorance had limited impact. smiley-neutral

-j

Ok, just checking.  I'll follow-up with an updated version that has the distance between the radio and SMA connector reduced to less than .3".

Thanks again for your input,

Brad.
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  Where can you purchase SkyTraq SUP500R modules or similar?  I am interested in building a GPS project but, I would like to get the parts from someone like Digi-key or Mouser.

 Nice work on your project so far!


Thanks,
Mark
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Salem, Oregon
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  Where can you purchase SkyTraq SUP500R modules or similar?  I am interested in building a GPS project but, I would like to get the parts from someone like Digi-key or Mouser.

Well I actually purchased mine directly from the source:  SkyTraq themselves.  The sample price of the SUP500R (or SUP500F) is $25 each, with a fixed FedEx shipping charge of $30 and a minimum order of $200.

Send a mail to info@skytraq.com.tw and Oliver will help you out.  I did a group order with the local dorks (http://dorkbotpdx.org/) paying for most of them and got enough interest to get the price to $27 each shipped (I purchased 16).

Shipping was quick and included a male header with each GPS - I thought that was a nice touch.  And sorry if I sound like a shill for SkyTraq, but I'm just a geek who was looking for a cheap GPS and they have great support (I've also used the Venus634FL​Px). 

Hard to beat the under $30 cost for a 3.3V GPS that can be powered from 3v-5v and supports HAB usage.

Quote

 Nice work on your project so far!

Thanks!  I'll post updated files later tonight; I'm going to spend the next week trying to work on the parts layout and improve the routing on the board.

Quote

Mark

Brad.

PS If you want one to play with, drop me a PM.  I've got a spare I'm probably not going to use I could let go for $30 shipped.
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Took a bit longer than I thought, but here is the revised board.

I tried to cleanup the layout a bit and keep it fairly cheap and simple to build.

I removed the (broken) Eagle files from the first post in this thread and have replaced them with the updated files.

Any comments would be appreciated.

Thanks,

Brad.


* miniTrackuinoRevisedSch.png (87.79 KB, 3262x2662 - viewed 33 times.)

* miniTrackuinoRevisedBd.png (65.91 KB, 1111x420 - viewed 25 times.)
* miniTrackuino.zip (34.68 KB - downloaded 12 times.)
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