[time-nuts] Z3810AS PPS to a Raspberry Pi

Pete Stephenson pete at heypete.com
Mon Mar 23 19:58:53 EDT 2015

On 3/23/2015 5:20 PM, Dan Watson wrote:
> The solution I came up with is very simple but works well. I
> capacitively couple the signal into a MOSFET which triggers a
> monostable 555 circuit. This generates a nice clean ~100ms pulse that
> I send to the PI, and an LED. Because who doesn't like blinking
> LEDs?
> I laid out a small PCB and ordered a few boards so that I can drop it
> right onto the GPIO header of the Pi. I have attached a picture of
> the board, as well as a capture of the input and output waveforms.

Looks nice: your surface-mount soldering looks great.

> The blue trace is the PPS signal from the GPSDO on the gate of the
> MOSFET, and the yellow trace is the output of the 555. After a couple
> days of settling, NTP stats on the Pi seem comparable to other GPSs
> I've tried, but I'll have to collect more data to really be sure of
> the performance. I think this circuit could also be used to translate
> PPS signals from other items of equipment to proper logic pulses.
> Lots more experimenting to do...

I've been looking at doing something similar once my Thunderbolt arrives.

Out of curiosity, how much does the 555 timer delay the PPS signal? Is
it consistent? What's the rise time?

> Anyway, if anyone is interested in more information about the circuit
> or board let me know. And comments are welcome.

I'd definitely be interested in the board. Any chance of modifying it
for through-hole components? My SMT soldering skills are pretty bad. If
you can send me the schematic I'd be happy to try modifying it for
through-hole components.


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