[time-nuts] Frequency counter recommendation

[Poul-Henning Kamp]

In message <4D0E3080.1060005 at earthlink.net>, jimlux writes:
>Bob Camp wrote:

>There are some nice solutions, though, using USB directly, which has the 
>advantage of providing a few watts of power.  Isolated DC/DC converters 
>are readily available.  you might be able to do transformer isolation of 
>the two data wires.

First: you want to use capacitors, not transformers.

Second: it is surprisingly tricky to get to work in practice, I have
only ever seen one device that managed to do so, and comply with
the USB standard, and the designer swore to never do it again.

People generally default to a small USB-enabled microcontroller
with an optocoupler to the real stuff.

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.