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

ROY PHILLIPS phill.r1 at btinternet.com
Sat Oct 21 14:50:27 UTC 2017

----Original message----
>From : hmurray at megapathdsl.net
Date : 21/10/2017 - 7:49 am (GMTDT)
To : gem at rellim.com
Cc : time-nuts at febo.com, hmurray at megapathdsl.net
Subject : Re: [time-nuts] inexpensive, black box, GPS or NTP based TTL time capture?

>>> 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?

>    # ppswatch /dev/pps0

That's a way to log stuff, but I don't think it comes under "Configure ntpd".

I remember some option to log lots of stuff, but I don't remember the 
details.  It could have been in a driver.  I couldn't find it in the man page 
for the PPS driver.

> Looks like $96 to me.  You can save some if you buy in bulk,

You can save $7 if you get the starter package that has only Pi, SD card, 
power, and case.  (Many starter packages include stuff you probably don't 
need and that raises the price.  But maybe one has a HDMI adapter.  I didn't 

Beware of using normal USB cables and/or normal USB power supplies.  The Pi 
is not happy with low voltage.  The drop in a USB cable can be significant.  
The setups intended for use with Pis normally have 5.1 or 5.25 volts and 
heavier gage wire in the cable.

[display, kbd, mouse...]
> Yeah, just for setup.  Shall we include the price of the desk it sits and
> the building it is in? 

I'm willing to assume somebody has a table and a roof.

The display and such are not a problem if you have a PC you can borrow them 
from.  (You probably need a HDMI adapter.)  But that doesn't work if all you 
have is a laptop or smart phone.

I think most of my friends have PCs but I wouldn't be surprised if some of 
them had a laptop and no PC.

If your PC is old enough, the keyboard and mouse may be PS2 rather than USB.

These are my opinions.  I hate spam.

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