[time-nuts] Designing an embedded precision GPS time server

Bob kb8tq kb8tq at n1k.org
Thu Oct 26 18:58:56 EDT 2017


Why go to the green? Just go with one of these Pocket Beagle’s I have sitting
here wondering what to do with them. They were just a bit under $20 when I 
picked them up. I doubt the price will climb over time …… Indeed you could
get two Pi Zero W’s for the pice of the Pocket Beagle. Lash an interface onto 
any of them (just like the Green) and get going. 

Is any of that cheaper once you get 1588 Ethernet going than a board (or chip) with
integrated Ethernet? My guess is no. 


> On Oct 26, 2017, at 5:26 PM, Iain Young <iain at g7iii.net> wrote:
> On 26/10/17 22:11, Chris Caudle wrote:
>> The processor you mentioned has a Cortex-M7 at 300MHz.  BBBB has a
>> Cortex-A8 running at 1GHz plus a Cortex-M processor available as a
>> coprocessor. Peripheral set is pretty comparable, and you can buy BBB at
>> retail for $50 which gets you the faster higher class processor, 512MB of
>> DRAM and 4GB of flash.  It runs linux right out of the box so you
>> basically  power it on and have NTP running.
> The BB Green is even better value for money, and why would we need HDMI
> for timing apps ? (It also simplifies doing my Poor man's TIC!)
>> On my list of projects to work on is a cape for BeagleBone Black that
>> takes 10MHz and 1PPS inputs along with a couple of RS232 converters for
>> the UARTs so you can connect a GPSDO to a BBB to make a time server.  In
>> my estimation that seemed like the best return on effort.
> Wheen you get around to it, *Please* consider:
>   1) multiplying that 10MHz up to 24 MHz as an option
>   2) RS422 option instead of RS232 (for the Lucent/HP GPS/Rb boxes)
>   3) PPS routed to TIMER4/5/6/7 rather than any old GPIO
>   4) Cover _all_ UARTS, even if serial headers are needed, rather than
> 9-pin D connectors
>   5) Some method of dropping a 5V PPS down to 3.3V (2N2222 comes to
> mind, as does a /2 voltage divider [2.5V is sufficient to trigger the
> GPIO pins], I have done both - and yes measured the delay through the
> 2N2222!)
> (Sorry Chris, I was looking at the serial cape options earlier today
> to try an santise my lash-ups, and was most disappointed!)
> Iain
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