[ntp:questions] Trying to use Dimension 4 time keeper

detha detha at foad.co.za
Mon Sep 16 05:50:22 UTC 2013


On Sun, 15 Sep 2013 18:56:26 +0100, David Taylor wrote:

> On 15/09/2013 18:37, unruh wrote:
> []
>> Yes, I saw it. Not sure what the voltages are on the Sure unit -- the
>> direct output of the PPS but I think 5V which is still a bit high. I
>> guess one could put a diode in series with the line to bring it down to
>> 3.3V.
> 
> I would recommend using a restive divider - perhaps 10K and 4.7K to start
> with - and monitoring the voltage into the Raspberry Pi.  Using resistors
> provides a current limit, and allows the voltage to get down to zero.  If
> the voltage is well below 3.3V, the upper 4.7 K resistor could be reduced.
>  Best to ask on one of the Raspberry Pi support groups as someone has
> likely already done the measurements.

http://jamesreubenknowles.com/level-shifting-stragety-experments-1741
might be of interest. For converting serial signals it works fine,
for PPS where one worries about being 100ns off maybe not so much.



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