Re: [Thumbgps-devel] Build vs. modify vs. what should we be doing anyway?

[Patrick Maupin <pmaupin@gmail.com>]

On Mon, Mar 12, 2012 at 4:03 PM, Eric S. Raymond <esr@thyrsus.com> wrote:

> I'm still skeptical about custom builds for production - means one of us
> would have to do the soldering, keep inventory, ship the results.  I'd rather
> develop a design and talk SparkFun or Dangerous Prototypes into fabbing it.

But if you work with somebody like this or like seedstudio, they will
order parts for you and assemble according to your instructions.  If
you simply view the dongle as a part to be ordered and the assembly to
be "take it apart, add this blue wire, put it back together" you will
realize that the same process could apply, at least for a company that
does more than basic board assembly.

> But an advantage of starting with this $23 module is that we don't have
> to make that decision yet.

Exactamundo!

> [Test system] sounds like a larger project than just reverse-engineering the dongle,
> though.  Do you have the capability, personally, to design and build such
> a thing?

This is more what I do on a daily basis.  Use a bunch of readily
available off-the-shelf thingies to make a few units.  In this case, I
would buy a third party FPGA board, make a couple of smaller PCBs to
talk to it with a socket for an OCXO, maybe a connector to accept a
clock from a rubidium time source, headers for some USB modules and
some GPS modules and do some FPGA coding to allow reliable high
resolution timestamps.  There are a couple of levels of this.  The
first is just to do some one-off futzing around looking at various
devices.  The second is to get serious.  You could probably build 3
identical units with really good resolution and stability (expensive
OCXO) for under $2K total.  Maybe a lot less if you can find some good
surplus stuff on ebay.

> And this makes complete sense.  Seems like a good way to start that doesn't
> require excessive time commitment up front on your part.

In that case I'll start ordering and plotting out what I'm going to
do, and will sign up for the project to start putting out information
on the test setup for people to throw rocks at.