[time-nuts] ARM boards for low-cost GPSDOs

Bob Camp lists at rtty.us
Sat Apr 12 19:50:32 UTC 2014


I’ve been working with some friends on an ARM based Arduino project. The support for ARM in the Arduino tool chain is still not really up to speed. It’s actually been faster / easier to take the stuff we need over to another board and tool chain than to fight through all of the gotchas within the Arduino / ARM world. The stuff is free / easy just about any way you do it.

At the chip level, the ARM’s have already overtaken many / most of the AVR’s that you would be using. 


On Apr 12, 2014, at 3:23 PM, Chris Albertson <albertson.chris at gmail.com> wrote:

> I have to agree.  At the hobby level I've been using board level products.
> Typically some guy in China buys the chips and any needed passive parts
> and builds a PCB.  Almost always the PCB will have a row of holes on the
> edge to fit a 0.1" header strip.   The board with shipping sells cheaper
> than the price of the parts.  (The Chinese sellers are using private
> mailing brokers who can aggregate large numbers of packages onto pallets,
> ship the pallets via low cost carries to a warehouse near a US post office.
> The packages are zip-code sorted and dropped into the USPO's pre-sorted
> bulk-mail system for just a few cents per package.)
> I think what prevents many people from using some uP parts is the tools.
> In the past they were complex but Arduino fixed that.  They made is VERY
> easy to get started and really set the bar for others.   Everyone else is
> catching up.     There really WAS a high cost of entry back when you needed
> to know how to edit text and send it to a compiler then a loader and  burn
> PROMs using special prom burner hardware.  All that complexity is now gone.
> Notice that new Arduino boards are ARM based and if you were foresightful
> enough to only use the features that are documented for Arduino your
> software can move directly to the new ARM board.  Many hobby programmers
> should not notice the difference when a CPU is changed.  They are writing
> in C/C++
> Today at the retail level AVR based Arduino is much less expensive.  You
> can buy one with shipping for under $4 and you can use a 9V "radio battery"
> for a power supply.   I've bought some for under $3.    But, yes some day
> ARM will move down into this price point.
> On Sat, Apr 12, 2014 at 9:23 AM, Bob Camp <lists at rtty.us> wrote:
>> Hi
>> Here's the issue about "big powerful 32 bit ARM processors"....
>> At the chip level (as in no board, just the bare part to solder down)
>> their are many parts below $1 and some below $0.50 in reasonable quantity
>> (say 10K).  It's hard to find a useful MCU of any sort below $0.25, so the
>> "premium" for an ARM is not very large. Depending on what you need for i/o,
>> the ARM may / may not be lower priced than the alternative. In a *lot* of
>> cases it is the low price option. There are many flavors of ARM and many
>> competing parts, so doing a full matrix to compare them all is a massive
>> undertaking. Indeed a Coretex M0 with 32K of flash is not the same thing as
>> an M4 or something bigger still. There are a lot of flavors of ARM.
>> At the semiconductor level, none of the manufacturers are going to state
>> it clearly, but it's becoming more and more clear. The support for (and
>> enhancement of) chips that are not based on ARM is going to dry up. It's
>> happening already if you watch the little details. It will be happening
>> more and more as time marches on. It will be *very* tough for an MCU over
>> about $1.00 a chip (at say 10K pcs) to compete with the ARM parts going
>> forward outside niche markets (like DSP).
>> No, it's not going to happen overnight. It will take a number of years for
>> things to work out.
>> ------
>> So why do a GPSDO on an ARM - They have staying power. The bang for the
>> buck is there. There are a lot of cheap boards out there with them already
>> set up and running on them. Nobody big is going back to leaded parts.
>> Semiconductor guys follow the big users. The future of "home project" work
>> with CPU's is to use a cheap board rather than a chip. The prices of the
>> boards will just keep coming down, they are not going to go up.... I can't
>> buy the parts on a $10 board for $30, let alone put them all together.
>> Pick a board and go with it. Put your *stuff* on a second board and plug
>> them together. Cheaper, faster, easier than DIY. You get USB / Ethernet /
>> whatever thrown in. With the right board (chip) you get flexible clocks and
>> PLL's that make the whole process a lot easier.
>> What's not to like?
>> Well yes, you need to dig into a tool chain. They either are free, or are
>> going to be free fairly soon now. There are even web based tools to do the
>> code stuff (mbed). You can't quite write it for one chip and drop it on
>> another one blindly. You do get locked (a bit) into your chip choice.
>> All in all, far more advantages than disadvantages.
>> Bob
>> On Apr 10, 2014, at 8:11 PM, Chris Albertson <albertson.chris at gmail.com>
>> wrote:
>>> I'm thinking about good reasons to build a GPSDO using something as big
>> and
>>> powerful as a 32-bit ARM processor.    I think the reason is that you are
>>> not really building a GPSDO but some other device that just happens to
>> have
>>> a GPSDO inside of it.
>>> For example you want to build a laser range finder and you need to
>> measure
>>> time of flight delay.  You'd need a very good clock and while you are at
>> it
>>> why not discipline the clock with GPS.      I could think of some radio
>>> experiments where I would want pairs of receivers with their local
>>> oscillators running in phase but many miles apart, so I'd build a GPSDO
>>> into the radio.    The ARM would support running the GPSDO, the bigger
>>> application and also remote access over the network or Internet.
>>> Today people mostly will build a stand alone GPSDO in a dedicated box and
>>> then connect the 10MHZ output to whatever is needed but now as we have
>>> seen, you can build a GPSDO completely in software, if your project
>> already
>>> has a computer then you can run a GPSDO inside an interrupt handler as a
>>> background task.  Adding GPSDO functionality to an existing product is
>>> almost trivially simple, just $2 in parts and some software if you
>> already
>>> have a CPU and OCXO as part of your system.
>>> Placing the GPSDO inside the product means the gpsdo can run at a
>> frequency
>>> that is more useful and needs no conversion.   So you can have the GPS
>>> control a 23 Mhz crystal if that is what your laser rangefinder needs.
>> Now
>>> that the cost of a GPSDO has fallen to $3 you can build them into
>>> "everything".  It no longer needs to be a shared device.
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> -- 
> Chris Albertson
> Redondo Beach, California
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