[time-nuts] inexpensive, black box, GPS or NTP based TTL time capture?

Bob Bownes bownes at gmail.com
Wed Oct 18 20:04:51 UTC 2017

A black box was asked for. Who cares what the OS inside is if you never
need to mess with it. A surprising number of things run linux variants.
Pretty much every smart phone is linux or unix...

What is the output format you would like for your timestamp? disk, network
file system, serial all can be made to work.

One could probably build 10-20 for a couple thousand dollars and make
enough to make it worth the trouble, depending on the output format of the

Pi Zero - $10
SD card - $8
GPS - $4
2x16 LCD display - $5
Enclosure - $15 for small box, $20 for ABS rack mount, $35 for aluminum
Hardware, nuts, bolts, screws, etc - $5
Power Supply - $5
Custom Interface card with buffering for TTL signal, other signal input
method, opto isolator, serial port for config & control, rs-232 out for
timestamp, serial and PPS from GPS, connectors, etc - $20-25 built.
Cables, etc - $5
Small rubber duck or GPS puck antenna $5

Ethernet, add $25.

Pi has USB/HDMI, but you can run it headless too.

Total BOM ~$100 (expensive case)
Development - ~week @$75/hr = $3,000 (board design, prototype, code +
Manufacturing, packaging, etc ~$50/unit

Shipped cost/unit, 20 units = $150materials, $150 labor = $300.
40 units = $225

Obviously BOM costs go down w volume, but you'd have to hit at least
quantity 50 to get a good break on enclosures and the custom boards.

So the big variable is how many will you need and what are you willing to
pay the developer. $75/hr is more or less going contract rates in my world.
$125-$150 not unheard of.

One off, no labor cost, cheap. Under $40 if you provide your own enclosure,
antenna, etc.

On Wed, Oct 18, 2017 at 3:26 PM, Hal Murray <hmurray at megapathdsl.net> wrote:

> > For under a $100 you could get a Raspberry Pi, a GPS HAT, and connect
> your
> > input to a GPIO pin.  Configure ntpd to log the real PPS and the input as
> > another 'PPS'.
> Is there an option to log all individual PPS events?
> The $100 for a Pi might be significantly low.  It depends on what you have
> in
> your toy box.
> Aside from the Pi and GPS HAT, you also need power and a micro SD card.
> For
> black box applications, you probably want a case.  You may need an external
> GPS antenna.
> For getting started, you also need:
>   SD card reader/writer
>   keyboard and mouse (Pi has USB)
>   display adapter (Pi is HDMI)
>   display
> I have an old KVM switch.  It uses PS2 rather than USB, so I need a PS2 to
> USB adapter.
> --
> These are my opinions.  I hate spam.
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